Errors & Solutions

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{width="3.813953412073491in" height="3.1279068241469816in"}{width="2.125in" height="0.3958333333333333in"} Hibernate Tutorial

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Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, SmlCodes.com, nor its dealers or distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

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If you discover any errors on our website or in this tutorial, please notify us at [email protected] or [email protected]

First published on Aug 2017, Published by **SmlCodes.com **

Author Credits

Name : Satya Kaveti

Email : [email protected]

Website : smlcodes.com, satyajohnny.blogspot.com

Digital Partners

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Hibernate Tutorial 1

TUTORIAL 1

1. Introduction 5

JDBC vs HIBERNATE 5

Hibernate Architecture 6

Hibernate Installation 8

2. Hibernate Example Step by Step 9

1. Choose Database Table 9

2. POJO class / Persistance class 9

3. Mapping File 10

4. Configuration File 11

5. Application class for main logic 12

Dialects in Hibernate 15

3. Hibernate CURD Operations 15

1. SELECT Operation using Hibernate 17

2. INSERT Operation using Hibernate 18

3. UPDATE Operation using Hibernate 19

4. DELETE Operation using Hibernate 20

4. Hibernate POJO Class Lifecycle 21

5. Hibernate Inheritance Mapping 22

1. Table per class hierarchy 25

2. Table per sub-class hierarchy 26

3. Table per concrete class hierarchy 28

6. Hibernate Generators <generator> 29

List of generators 29

Generators Example 33

7. Hibernate Query Language (HQL) 35

SQL vs HQL 35

Query Interface 36

HQL Examples 36

HQL with Aggregate functions 40

8. Hibernate Criteria Query Language(HCQL) 41

Working with Criteria Query Language 41

Hibernate Projections 45

9. Native SQL Queries 47

Working with Native SQL Queries 47

10. Named Queries 49

11. Hibernate Relationships 52

Relationships in Hibernate 53

1.One-to-One Relationship Mapping Example 54

2.One-to-Many / Many-to-One Relationship 57

3.Many to Many Relationship 60

12. Hibernate Cache 63

13. Hibernate with Annotations 67

Commonly used Annotations in Hibernate 67

Example : CURD oprations using Annotations 68

Mappings using Annotations 71

Errors & Solutions 77

org.hibernate.HibernateException: Could not parse configuration: hibernate.cfg.xml 77

References 77

Introduction ===============

Hibernate is the ORM tool given to transfer the data between a java (object) application and a database (Relational) in the form of the objects. Hibernate is the open source light weight tool given by Gavin King.

Hibernate is a non-invasive framework, means it won't force the programmers to extend/implement any class/interface, and in hibernate we have all POJO classes so its light weight

JDBC vs HIBERNATE

JDBC HIBERNATE

Programmer must close the connection. Jdbc doesn't responsible to close the connection. Hibernate will take care about closing the connections if the table structure is modified then the JDBC program doesn't work, again we need to modify and compile the programs Hibernate has its own query language(HQL) and it is database independent. So if we change the database, then also our application will work, because HQL is database independent In jdbc all exceptions are checked exceptions, so we must write code in try, catch and throws hibernate we have only Un-checked exceptions, so no need to write try, catch, or throws JDBC won't generate primary keys automatically Hibernate has capability to generate primary keys automatically while we are storing the records into database. JDBC won't support Caching mechanism Hibernate supports caching mechanism by this, the number of round trips between an application and the database will be reduced, by using this caching technique an application performance will be increased automatically. In JDBC , we need to write SQL queries manually Hibernate provided Dialect classes, so we no need to write sql queries in hibernate, instead we use the methods provided by that API

Hibernate Architecture

The diagram below provides a high-level view of the Hibernate architecture:

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="2.9375in" height="3.173173665791776in"}

Following is a detailed view of the Hibernate Application Architecture

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="5.26451990376203in" height="5.135416666666667in"}

Hibernate uses various existing Java APIs, like JDBC, Java Transaction API(JTA), and Java Naming and Directory Interface (JNDI) along with its own API objects like SessionFactory, Session, Transaction etc.,

1. Configuration

It represents a configuration or properties file required by the Hibernate. Configuration is the file loaded into hibernate application when working with hibernate.

Configuration file contains 3 types of information.

i. Connection Properties

ii. Hibernate Properties

iii. Mapping file name(s)

<? xml version='1.0' encoding='utf-8'?>

<! DOCTYPE hibernate-configuration PUBLIC

"-//Hibernate/Hibernate Configuration DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd\"\>

<hibernate-configuration>

<session-factory>

<! -- Database connection settings -->

<property name="connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="connection.url">jdbc:mysql://localhost:3306/mydb</property>

<property name="dialect">org.hibernate.dialect.MySQLDialect</property>

<property name="hbm2ddl.auto">validate</property>

</session-factory>

</hibernate-configuration>

How do you switch between relational databases without code changes?

Using Hibernate SQL Dialects, we can switch databases. Hibernate will generate appropriate hql queries based on the dialect defined.

What is hibernate dialect class vs Driver

Driver: A database driver is a program for which implements a protocol (ODBC, JDBC) for connecting to a database. It is an Adaptor which connects a generic interface to a specific vendor's implementation, just like printer drivers etc.
"Driver is like English"

Dialect : A database dialect is a configuration setting for platform independent software (JPA, Hibernate, etc) which allows such software to translate its generic SQL statements into vendor specific DDL, DML.
"Dialect is the different pronunciations of English"

We all know there are different versions of Oracle... Oracle 9i, Oracle8, Oracle 10g.The driver we would use would be a common for all of these. But the dialect we use is specific to each one of them, which helps Hibernate in generating optimized queries to those specific versions of database and also this is not mandatory to be given in cfg.xml.

This is the SQL dialect (database type) for the database being used.

For connecting any hibernate application with the database, you must specify the SQL dialects. There are many Dialects classes defined for RDBMS in the org.hibernate.dialect package. They are as follows:

RDBMS Dialect

Oracle (any version) org.hibernate.dialect.OracleDialect Oracle9i org.hibernate.dialect.Oracle9iDialect Oracle10g org.hibernate.dialect.Oracle10gDialect MySQL org.hibernate.dialect.MySQLDialect MySQL with InnoDB org.hibernate.dialect.MySQLInnoDBDialect MySQL with MyISAM org.hibernate.dialect.MySQLMyISAMDialect DB2 org.hibernate.dialect.DB2Dialect DB2 AS/400 org.hibernate.dialect.DB2400Dialect DB2 OS390 org.hibernate.dialect.DB2390Dialect Microsoft SQL Server org.hibernate.dialect.SQLServerDialect SAP DB org.hibernate.dialect.SAPDBDialect Informix org.hibernate.dialect.InformixDialect

2. SessionFactory Object

It holds second level cache (optional) of data like Dialect, username and password. All these data are fixed for whole application, so it is immutable. And if many threads access at same time there is no change in data, so it is thread safe. The org.hibernate.SessionFactory interface provides factory method to get the object of Session

3. Session Object

It Opens a Session between Database and our Application. It holds a first-level cache (mandatory) of data. The org.hibernate.Session interface provides methods to insert, update and delete the object

Session is a light weight and a non-threadsafe object (No, you cannot share it between threads) that represents a single unit-of-work with the database

4. Transaction Object

The org.hibernate.Transaction interface provides methods for transaction management.

5. Query Object

Query objects use SQL or Hibernate Query Language (HQL) string to retrieve data from the database and create objects.

6. Criteria Object

Criteria object are used to create and execute object oriented criteria queries to retrieve objects.

Hibernate Installation

Working with the framework software is nothing but, adding the .jar(s) files provided by that framework to our java application. We can add hibernate jars in two ways

1.Hibernate install using maven

We just need to add hibernate maven dependencies in pom.xml

<groupId>org.hibernate</groupId>

<artifactId>hibernate-core</artifactId>

<version>5.2.10. Final</version>

</dependency>

2. Download Hibernate jars & add to project

Download jar from hibernate.org / from here & extract the zip file. We don't need to add all the jars. We need to add following jars.

Anttr-2.7.6.jar
asm.jar
asm-attrs.jar
cglib-2.1.3.jar
commons-collections-2.1.1.jar
commons-logging-1.0.4.jar
ehcash.jar
dom4j-1.6.1.jar
hibernate3.jar
jta.jar
log4j-1.2.3.jar

along with the hibernate jars we must include one more jar file, which is nothing but related to our database, this is depending on your database

Hibernate Example Step by Step =================================

For Developing any hibernate application we need create below 4 files always

Choose Database Table
POJO class
Mapping XML
Configuration XML
Application class for main logic

Above are the minimum requirement to run any hibernate application, but we may create any number of POJO classes and any number of mapping xml files (Number of POJO classes = that many number of mapping xmls), and only one configuration xml and finally one java file to write our logic.

Choose Database Table

In this Example we are taking 'employee' table of 'mydb' database.

CREATE TABLE `employee` (

`eid` INT(11) NOT NULL AUTO_INCREMENT,

`name` VARCHAR(50) NOT NULL DEFAULT '0',

`address` VARCHAR(50) NOT NULL DEFAULT '0',

PRIMARY KEY (`eid`)

)

COLLATE='latin1_swedish_ci'

ENGINE=InnoDB

AUTO_INCREMENT=5

;

mysql> select * from employee;

+-----+-------+------------+

| eid | name | address |

+-----+-------+------------+

| 1 | SATYA | VIJAYAWADA |

| 2 | SURYA | HYDERABAD |

| 3 | RAVI | PUNE |

+-----+-------+------------+

POJO class / Persistance class

POJO is a simple java file, no need to extend any class or implement any interface.
Pojo class contains **table column names as data members, **
In above table eid, name, address are columns
It contains column names as private data members with setters and getters

EmployeeBo.java

package bo;

public class EmployeeBo {

private int eid;

private String name;

private String address;

public int getEid() {

return eid;

}

public void setEid(int eid) {

this.eid = eid;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getAddress() {

return address;

}

public void setAddress(String address) {

this.address = address;

}

Mapping File

Mapping file contains mapping from a pojo class name to a table name and pojo class variable names to table column names.
We can create any no. of mapping files
Mapping can be done using 2 ways, using XML & using Annotations.

[Syntax of mapping xml (Pojaclassname.hbm.xml)]{.underline}

<hibernate-mapping>

</class>

</hibernate-mapping>

[Example: EmployeeBo.hbm.xml]{.underline}

<hibernate-mapping>

</id>

</class>

</hibernate-mapping>

[Explanation]{.underline}

<hibernate-mapping> is the root element in the mapping file.
<class/> specifies the Persistent/POJO class.
<id/> specifies the primary key attribute in the class.
<generator> is the sub element of id. It is used to generate the primary key. There are many generator classes such as assigned (It is used if id is specified by the user), increment, hilo, sequence, native etc. We will learn all the generator classes later.
property It is the subelement of class that specifies the property name of the Persistent class.

Configuration File

Configuration file contains 3 types of information.

i. Connection Properties

ii. Hibernate Properties

iii. Mapping file name(s)

We must create configuration file for each database we are going to use.

No. of databases we are using = That many number of configuration files

[Syntax of Configuration file]{.underline}

<hibernate-configuration>

<session-factory>

<property name="connection.driver_class">Driver Class Name </property>

<property name="connection.password">password</property>

<property name="show_sql">true/false</property>

<property name="dialet">Database dialet class</property>

<property name="hbm2ddl.auto">create/update or what ever</property>

</session-factory>

</hibernate-configuration>

[Example: hibernate.cfg.xml]{.underline}

<?xml version='1.0' encoding='UTF-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

"-//Hibernate/Hibernate Configuration DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd\"\>

<hibernate-configuration>

<session-factory>

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/smlcodes</property>

<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

<property name="hbm2ddl.auto">update</property>

</session-factory>

</hibernate-configuration>

Application class for main logic

We will create our application class with the main() method to run the application. We will use this application to save Employee data. Please follow the steps to write Application class

1. Load Hibernate API into Our Application

Load hibernate API by writing these two lines on the top of the application.

import org.hibernate.*;

import org.hibernate.cfg.*;

2. Load Configurations

Among Configuration(hibernate.cfg.xml), Mapping xml files, first we need to load configuration xml, because once we load the configuration file, automatically mapping xml file will also load, because it is defined it Configuration(hibernate.cfg.xml) file

We can load the configuration file by using Configuration class Object. cfg.configure("xml") loads the all the configurations from config file and save in config object, now config object contains all configuration details.

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

3. Open Session

SessionFactory will produces the Session objects based on the requests. To get Session Object we have to call openSession() method on Sessionfactory Object.

Usually an application has a single SessionFactory instance and threads servicing client requests obtain Session instances from this factory.

Whenever session is opened then internally a database connection will be opened

SessionFactory factory = cfg.buildSessionFactory();

Session session = factory.openSession();

4. Create Transaction Object

While working with insert, update, delete, operations from a hibernate application onto the database then hibernate needs a logical Transaction, if we are selecting an object from the database then we do not require any logical transaction in hibernate.

To begin a logical transaction in hibernate then we need to call a method beginTransaction() given by Session Interface

Transaction tx = session.beginTransaction();

session.save(bo);

System.out.println("Employee Data saved successfully.....!!");

tx.commit();

We have following methods for performing CURD operations

session.save(bo) - Inserting object "bo"into database

session.update(bo) - Updating object "bo" in the database

session.load(bo) - Selecting object "bo" object

session.delete(bo) - Deleting object "bo"from database

Finally we need to call **commit() **in Transaction, like tx.commit();

5. Close the Connections

Finally we need to close the all opend connections

session.close();

factory.close();

[Example : EmployeeSave.java]{.underline}

package app;

import org.hibernate.*;

import org.hibernate.cfg.*;

import bo.EmployeeBo;

public class EmployeeSave {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory factory = cfg.buildSessionFactory();

Session session = factory.openSession();

EmployeeBo bo = new EmployeeBo();

bo.setEid(5);

bo.setName("DILEEP");

bo.setAddress("BANGLORE");

Transaction tx = session.beginTransaction();

session.save(bo);

System.out.println("Employee Data saved successfully.....!!");

tx.commit();

session.close();

factory.close();

}

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).

log4j:WARN Please initialize the log4j system properly.

Employee Data saved successfully.....!!

Hibernate: insert into employee (name, address, eid) values (?, ?, ?)

Summarized Steps for creating Application class

Configuration

SessionFactory

Session

Transaction

Close Statements

Hibernate CURD Operations ============================

Now we will see how to insert, delete, update & select data from/into database using hibernate. Below files are common to all CURD operation examples, follow the Steps

1. Choose Database Table

mysql> select * from employee;

+-----+--------+-------------+

| eid | name | address |

+-----+--------+-------------+

| 1 | Satya | VIJYAYAWADA |

| 2 | Ravi | HYDERABAD |

| 3 | SURYA | HYDERABAD |

| 4 | RAMAN | PUNE |

| 5 | DILEEP | BANGLORE |

| 6 | DILEEP | BANGLORE |

+-----+--------+-------------+

2. POJO class(EmployeeBo.java)

package bo;

public class EmployeeBo {

private int eid;

private String name;

private String address;

**//Setters& getters **

}

3. O/R Mapping XML(EmployeeBo.hbm.xml)

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping SYSTEM

"hibernate-mapping-3.0.dtd">

<hibernate-mapping>

</id>

</class>

</hibernate-mapping>

4. Hibernate Configuration file

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration SYSTEM

"hibernate-configuration-3.0.dtd">

<hibernate-configuration>

<session-factory>

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="hibernate.connection.url">jdbc:mysql://[localhost]{.underline}:3306/[smlcodes]{.underline}</property>

<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

<property name="hbm2ddl.auto">update</property>

</session-factory>

</hibernate-configuration>

SELECT Operation using Hibernate

We have following methods to perform SELECT Operation in Hibernate

Object load(Class theClass, Serializable id)

Load() example

package curd;

import org.hibernate.*;

import org.hibernate.cfg.*;

import bo.EmployeeBo;

public class EmployeeSelect {

public static void main(String[] args) {

//1.Load Configuration

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

//2.Create Session

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

//3.Perform Operations

Object ob = session.load(EmployeeBo.class, new Integer(1));

EmployeeBo bo = (EmployeeBo) ob;

System.out.println("SELECTED DATA\n ================");

System.out.println("EID : "+bo.getEid());

System.out.println("NAME : "+bo.getName());

System.out.println("ADDRESS : "+bo.getAddress());

}

log4j:WARN No appenders could be found for logger org.hibernate.cfg.Environment).

log4j:WARN Please initialize the log4j system properly.

Hibernate: select employeebo0_.eid as eid0_0_, employeebo0_.name as name0_0_, employeebo0_.address as address0_0_ from employee employeebo0_ where employeebo0_.eid=?

SELECTED DATA

================

EID : 1

NAME : Satya

ADDRESS : VIJYAYAWADA

Get() example

############################## [Difference between get() vs load() method in Hibernate? (detailed answer)]{.underline}

The key difference between get() and load() method is that

load() will throw an exception if an object with id passed to them is not found
get() will return null.

Another important difference is that load can return proxy without hitting the database unless required (when you access any attribute other than id) but get() always go to the database, so sometimes using load() can be faster than the get() method. It makes sense to use the load() method if you know the object exists but get() method if you are not sure about object's existence.

Parameter get load

Database retrieval It always hits the database It does not hit database If null If it does not get the object with id, it returns null If it does get the object with id, it throws ObjectNotFoundException Proxy It returns real object It returns proxy object Use If you are not sure if object with id exists or not, you can use get If you are sure about existence of object, you can use load

[What is the difference between save() and persist() method in Hibernate?]{.underline}

Serializable Object save() returns a Serializable object

void persist() method is void, so it doesn't return anything.

INSERT Operation using Hibernate

We have Following methods to perform insert Operation in Hibernate

Serializable **save(Object object) **
void **persist(Object object) **
void **saveOrUpdate(Object object) **

package curd;

public class EmployeeInsert {

public static void main(String[] args) {

// 1.Load Configuration

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

// 2.Create Session

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

// 3.Create Transaction Object

Transaction tx = session.beginTransaction();

EmployeeBo ob1 = new EmployeeBo(12, "KARTHIK", "ONGOLE");

session.save(ob1);

tx.commit();

tx.begin();

EmployeeBo ob3 = new EmployeeBo(10, "NAG", "HYD");

session.saveOrUpdate(ob3);

tx.commit();

EmployeeBo ob2 = new EmployeeBo(11, "PERSIST", "VIZAG");

session.persist(ob2);

System.out.println("Data Saved Sussesfully");

session.close();

sf.close();

}

mysql> select * from employee;

+-----+---------+-------------+

| eid | name | address |

+-----+---------+-------------+

| 1 | Satya | VIJYAYAWADA |

| 2 | Ravi | HYDERABAD |

| 3 | SURYA | HYDERABAD |

| 4 | RAMAN | PUNE |

| 5 | DILEEP | BANGLORE |

| 6 | DILEEP | BANGLORE |

| 7 | ANANTH | CHENNAI |

| 8 | vijay | CHENNAI |

| 9 | KARTHIK | ONGOLE |

| 10 | NAG | HYD |

| 12 | KARTHIK | ONGOLE |

+-----+---------+-------------+

UPDATE Operation using Hibernate

We have two approaches for updating already saved data in database.

Approach 1:

In this approach we load the existing row, and we will set the appropriate properties. On committing transaction hibernate automatically updates the data. But this is not recommended.

Approach 2:

In this approach to modify object in the database, we need to create new object with same id and we must call update() given by session interface

We have following method to perform UPDATE Operation in Hibernate

void update(Object object)

package curd;

public class EmployeeUpdate {

public static void main(String[] args) {

// 1.Load Configuration

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

// 2.Create Session

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

//======Approach 1 ==========

Transaction tx = session.beginTransaction();

EmployeeBo ob1 = (EmployeeBo)session.load(EmployeeBo.class, new Integer(4));

ob1.setAddress("VIJAYAWADA");

tx.commit();

//======Approach 2 ==========

tx = session.beginTransaction();

EmployeeBo ob2 = new EmployeeBo(new Integer(5), "ANANTH", "HYDERABAD");

session.update(ob2);

tx.commit();

System.out.println("Update Completed!");

session.close();

sf.close();

}

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="5.427083333333333in" height="1.6666666666666667in"}

############################## What is the difference between and merge and update?

Use update() if you are sure that the session does not contain an already persistent instance with the same identifier, and merge() if you want to merge your modifications at any time without consideration of the state of the session.

DELETE Operation using Hibernate

We have following method to perform DELETE Operation in Hibernate

void delete(Object object)

package curd;

import bo.EmployeeBo;

public class EmployeeDelete {

public static void main(String[] args) {

// 1.Load Configuration

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

// 2.Create Session

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

//======Load the Object & DELETE ==========

Transaction tx = session.beginTransaction();

EmployeeBo bo =(EmployeeBo)session.load(EmployeeBo.class, new Integer(4));

session.delete(bo);

tx.commit();

session.close();

sf.close();

}

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="5.395833333333333in" height="1.6458333333333333in"}

Hibernate POJO Class Lifecycle =================================

In Hibernate POJO class (Persistance class) object will have 3 States

Transient state
Persistent state
Detached state

1. Transient state

Whenever an object of a pojo class is created then it will be in the Transient state
When the object is in a Transient state it doesn't represent any row of the database
If we modify the data of a pojo class object, when it is in transient state then it doesn't effect on the database table

2. Persistent state

When the object is in persistent state, then it represents one row of the database
if the object is in persistent state then it is associated with the unique Session

3. Detached state

After Persistent State Object will goes under Dethatched State
if we want to move an object from persistent to detached state, we need to do either closing that session or need to clear the cache of the session

package curd;

public class POJOLifeCycle {

public static void main(String[] args) {

// 1.Load Configuration

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

// 2.Create Session

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

//======1.Transient State START==========

EmployeeBo bo = new EmployeeBo();

bo.setEid(6);

bo.setName("RAJESH");

bo.setAddress("NEWYORK");

//======1.Transient State END==========

//======2.Persistent state START==========

Transaction tx = session.beginTransaction();

session.save(bo);

tx.commit();

//======2.Persistent state END==========

//========3.Detached State START========

session.close();

bo.setEid(7);

bo.setName("MADHU");

bo.setAddress("COLOMBO");

//========3.Detached State END========

sf.close();

}

Hibernate Inheritance Mapping ================================

In hibernate inheritance, if we have base and derived classes, now if we save derived(sub) class object, base class object will also be stored into the database.

Hibernate supports 3 types of Inheritance Mappings:

Table per class hierarchy
Table per sub-class hierarchy
Table per concrete class hierarchy

We will understand one by one with examples. Below tables are used in upcoming examples.

CREATE TABLE `vehicle` (

`vid` INT(11) NOT NULL AUTO_INCREMENT,

`price` DOUBLE NOT NULL DEFAULT '0',

PRIMARY KEY (`vid`));

CREATE TABLE `bike` (

`type` VARCHAR(50) NULL DEFAULT NULL

);

CREATE TABLE `car` (

`type` VARCHAR(50) NULL DEFAULT NULL

);

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="5.010416666666667in" height="3.6875in"}

Following files are common to all examples, only we need to change mapping xml & Application class

[Vehicle.java]{.underline}

package inheritance;

public class Vehicle {

private int vid;

private double price;

public int getVid() {

return vid;

}

public void setVid(int vid) {

this.vid = vid;

}

public double getPrice() {

return price;

}

public void setPrice(double price) {

this.price = price;

}

[Bike.java]{.underline}

package inheritance;

public class Bike extends Vehicle {

private String biketype;

public String getBiketype() {

return biketype;

}

public void setBiketype(String biketype) {

this.biketype = biketype;

}

[Car.java]{.underline}

package inheritance;

public class Car extends Vehicle {

private String cartype;

public String getCartype() {

return cartype;

}

public void setCartype(String cartype) {

this.cartype = cartype;

}

[hibernate.cfg.xml]{.underline}

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration SYSTEM

"hibernate-configuration-3.0.dtd">

<hibernate-configuration>

<session-factory>

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="hibernate.connection.url">jdbc:mysql://[localhost]{.underline}:3306/[smlcodes]{.underline}</property>

<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

<property name="hbm2ddl.auto">update</property>

</session-factory>

</hibernate-configuration>

[InheritanceCommonApp.java]{.underline}

package inheritance;

import org.hibernate.*;

import org.hibernate.cfg.*;

public class TablePerClassExample {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory factory = cfg.buildSessionFactory();

Session session = factory.openSession();

Bike bike = new Bike();

bike.setVid(101);

bike.setBiketype("HONDA");

bike.setPrice(50000);

Car car = new Car();

car.setVid(102);

car.setCartype("MARUTHI");

car.setPrice(600000);

Transaction tx = session.beginTransaction();

session.save(bike);

session.save(car);

tx.commit();

session.close();

factory.close();

}

Table per class hierarchy

If we save the derived class object in the database, then automatically base class data will also be saved into the database in base class Table

For example, if we save the derived class object like Car or Bike then automatically Vehicle class object will also be saved into the database, and in the database all the data will be stored into a single table only, which is base class table.

For this type of hierarchy, we must use one extra discriminator column in the database, to identify which derived class object we have been saved in the table along with the base class object, if we are not using this column hibernate will throws the exception.

[Vehicle.hbm.xml]{.underline}

<hibernate-mapping>

</subclass>

</subclass>

</class>

</hibernate-mapping>

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="5.260693350831146in" height="2.3854166666666665in"}

We added one new line discriminator, after the id element just to identify which derived class object we have been saved in the table. Here everything has been saved in a single table(vehicle)

Table per sub-class hierarchy

In this type of hierarchy**, if we save the Base class object, first hibernate will saves the Base class object into the base class table**, then it will save the subclass object data into subclass table. Here first it will save data into Base class table.

In below Example, if we save the Car/Bike class object, first hibernate will saves the data related to Vehicle class object into the vehicle table and then Car/Bike object data in Car/Bike related tables.so we can say, No. of classes equals to No. of Tables

No. of classes = No. of Tables

Here <joined-subclass> element of <class> is used to map the child class with parent class using the primary key and foreign key relation

[Vehicle.hbm.xml]{.underline}

<hibernate-mapping>

<joined-subclass name="inheritance.Bike" table="bike">

</joined-subclass>

<joined-subclass name="inheritance.Car" table="car">

</joined-subclass>

</class>

</hibernate-mapping>

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="5.0in" height="3.7291666666666665in"}

Once we save the derived class object, then hibernate will first save the base class object then derived class object.
At the time of saving the derived class object, hibernate will copy the primary key value of the base class into the corresponding derived class, by using <key> tag. From the above output
- 102 copied into CAR_KEY column of car table
- 101 copied into BIKE_KEY column of the bike table

Table per concrete class hierarchy

Once we save the derived class object, then derived class data and base class data will be saved in the derived class related table in the database
for this type we need the tables for derived classes, but not for the base class
we need to use one new element <union-subclass> under <class>

[Vehicle.hbm.xml]{.underline}

<hibernate-mapping>

<union-subclass name="inheritance.Bike" table="bike">

</union-subclass>

<union-subclass name="inheritance.Car" table="car">

</union-subclass>

</class>

</hibernate-mapping>

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="5.0in" height="2.7916666666666665in"}

Hibernate Generators <generator> =====================================

The <generator> subelement of id used to generate the unique identifier for the objects of persistent class. There are many generator classes defined in the Hibernate Framework.

[Example:]{.underline}

<hibernate-mapping>

</id>

</class>

</hibernate-mapping>

In Above example class="assigned" means, while inserting data into database user will take care about generating Primary key value. But, hibernate can also generate the primary keys without user interaction, by using Generators.

List of generators

hibernate using different primary key generator algorithms, for each algorithm internally a class is created by hibernate for its implementation
hibernate provided different primary key generator classes and all these classes are implemented from org.hibernate.id.IdentifierGeneratar Interface

The following are the list of main generators we are using in the hibernate framework

assigned
increment
sequence
identity
hilo
native
foregin
**uuid **

1.assigned

This is the default generator class used by the hibernate, if we do not specify <generator > element under id element then hibernate by default assumes it as "assigned"
If generator class is assigned, then the programmer is responsible for assigning the primary key value to object which is going to save into the database

<class name="bo.EmployeeBo" table="employee">

<id name="eid" column="eid">

<generator class="assigned" />

</id>

<property>....</property>

</class>

2.increment

First select the max id if there, if no 1 as max
for each record it increments by 1 (i++)
Increment will take care by Application Layer[Hibernate]

</id>

</class>

3.identity

First select the max id if there, if no 1 as max
for each record it increments by 1 (i++)
Increment will have taken care by DB Layer[MySQL]
MySQL, DB2 Support this. Oracle Won't Support it.

</id>

</class>

4.sequence

while inserting a new record in a database, hibernate gets next value from the sequence under assigns that value for the new record
If programmer has created a sequence in the database, then that sequence name should be passed as the generator
Sequence start with 1 and Incremented by 1
Internally it creates Sequence table, and increment operations done here
Increment will take care by Both Application Layer[Hibernate] & DB Layer[MySQL]
MySQL, DB2 Support this. Oracle Wont

</id>

</class>

For defining your own sequence, use the param subelement of generator.

<param name="sequence">USER_DEFIED_SEQUENCE</param>

</id>

</class>

5.hilo

hilo start with 0
Internally it creates hilo table
It will take High value form Hilo table, and it will Increment
for each Deployment/Restart application, High value increment by 32768
1 st Deploy: 1,2,3,4...
2 nd Deploy: 32768,32769..........
MySQL, DB2 Support this. Oracle Won't Support it.

</id>

</class>

6.native

when we use this generator class, it first checks whether the database supports identity or not, if not checks for sequence and if not, then hilo will be used finally the order will be.

identity
sequence
hilo

</id>

</class>

7.foregin

It uses the id of another associated object, mostly used with <one-to-one> association.

8.uuid

It uses 128-bit UUID algorithm to generate the id. The returned id is of type String, unique within a network (because IP is used). The UUID is represented in hexadecimal digits, 32 in length.

Custom generator

For ur application, you want to generate keys as per ur wish like icici_101, icici_102, icici_103, ..........

write IciciGenerator class implementing IdentityGenerator
override generate method
and write logic for keys

</id>

</class>

Generators Example

[EmployeeBo.java]{.underline}

package bo;

public class EmployeeBo {

private int eid;

private String name;

private String address;

//Setters & Getters

}

[GeneratorsExample.java]{.underline}

package app;

import org.hibernate.*;

import org.hibernate.cfg.*;

import bo.EmployeeBo;

public class GeneratorsExample {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory factory = cfg.buildSessionFactory();

Session session = factory.openSession();

EmployeeBo bo = new EmployeeBo();

//bo.setEid(100);

bo.setName("sequence");

bo.setAddress("BANGLORE");

Transaction tx = session.beginTransaction();

session.save(bo);

tx.commit();

session.close();

factory.close();

}

[EmployeeBo.hbm.xml]{.underline}

<hibernate-mapping>

</id>

</class>

</hibernate-mapping>

Here we are changing generator classes one-by-one, check the how data stored in DB in output window.

[hibernate.cfg.xml]{.underline}

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration SYSTEM

"hibernate-configuration-3.0.dtd">

<hibernate-configuration>

<session-factory>

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="hibernate.connection.url">jdbc:mysql://[localhost]{.underline}:3306/[smlcodes]{.underline}</property>

<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

<property name="hbm2ddl.auto">update</property>

</session-factory>

</hibernate-configuration>

[Output]{.underline}

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="4.677083333333333in" height="2.0104166666666665in"}

For Sequence,

Exception in thread "main" [org.hibernate.MappingException]{.underline}: could not instantiate id generator

at org.hibernate.id.IdentifierGeneratorFactory.create([IdentifierGeneratorFactory.java:98]{.underline})

Hibernate Query Language (HQL) =================================

Hibernate Query Language (HQL) is same as SQL (Structured Query Language) but it doesn't depend on the table of the database. Instead of table name, we use class name in HQL. So it is database independent query language

HQL is database independent, means if we write any program using HQL commands then our program will be able to execute in all the databases without doing any further changes to it.
HQL supports object oriented features like **Inheritance, polymorphism, Associations (**Relationships)

SQL vs HQL

If we want to select a Complete Object from the database, we use POJO class reference in place of *** **while constructing the query

// In SQL

sql> select * from Employee

Note: Employee is the table name.

// In HQL

hql> select s from EmployeeBo s

[ or ]

from EmployeeBo s

Note: here s is the reference of EmployeeBo

If we want to load the Partial Object from the database that is only selective properties of an objects, then we need to replace column names with POJO class variable names

// In SQL

sql> select eid,name,address from Employee

Note: eid,name,address are the columns of Employee the table.

// In HQL

hql> select s.eid,s.name,s.address from EmployeeBo s

It is also possible to select the object from the database by passing run time values into the query using " ? "

//In SQL

sql> select * from employee where eid=?

// In HQL

hql> select s from EmployeeBo s where s.eid=?

[ or ]

select s from EmployeeBo s where s.eid =:101

Query Interface

If we want to execute a HQL query on a database, we need to create a Query interface object. To get query object, we need to call session. createQuery() method in the session Interface.

Following are the most commonly used methods in Query interface

public int executeUpdate() -is used to execute the update or delete query.
public List list() -returns the result of the relation as a list.
public Query setFirstResult(int rowno) - row number from where record will be retrieved.
public Query setMaxResult(int rowno) - no. of records to be retrieved from the relation (table).
public Query setParameter(int position, Object value) it sets the value to query parameter.
public Query setParameter(String name, Object value) it sets the value to a named query param.

[Synatx:]{.underline}

Query qry = session.createQuery("--- HQL command ---");

List l = qry.list();

Iterator it = l.iterator();

while(it.hasNext())

{

Object o = it.next();

EmployeeBo s = (EmployeeBo)o;

----- ------- ---------

}

HQL Examples

Following files are common to all the examples

[Table :bank]{.underline}

CREATE TABLE `bank` (

`accno` INT(11) NOT NULL AUTO_INCREMENT,

`accname` VARCHAR(50) NULL DEFAULT NULL,

`balance` DOUBLE NULL DEFAULT NULL,

PRIMARY KEY (`accno`)

)

ENGINE=InnoDB

;

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="2.6666666666666665in" height="0.96875in"}

[BankBo.java]{.underline}

package hql;

public class BankBo {

private int accno;

private String accname;

private double balance;

public int getAccno() {

return accno;

}

public void setAccno(int accno) {

this.accno = accno;

}

public String getAccname() {

return accname;

}

public void setAccname(String accname) {

this.accname = accname;

}

public double getBalance() {

return balance;

}

public void setBalance(double balance) {

this.balance = balance;

}

[BankBo.hbm.xml]{.underline}

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping SYSTEM "hibernate-mapping-3.0.dtd">

<hibernate-mapping>

</class>

</hibernate-mapping>

[hibernate.cfg.xml]{.underline}

<hibernate-configuration>

<session-factory>

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="hibernate.connection.url">jdbc:mysql://[localhost]{.underline}:3306/[smlcodes]{.underline}</property>

<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

</session-factory>

</hibernate-configuration>

1. HQL Select Query Example

package hql;

import java.util.Iterator;

import java.util.List;

import org.hibernate.Query;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.Configuration;

import org.hibernate.classic.Session;

public class HQLSelect {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory factory = cfg.buildSessionFactory();

Session session = factory.openSession();

System.out.println("====1.Selecting Complete Object====== ");

Query query = session.createQuery("Select b from BankBo b");

[List]{.underline} list = query.list();

[Iterator]{.underline} it = list.iterator();

while (it.hasNext()) {

BankBo bo = (BankBo) it.next();

System.out.println("------------------------");

System.out.println("ACC No : " + bo.getAccno());

System.out.println("Name : " + bo.getAccname());

System.out.println("Balance : " + bo.getBalance());

}

System.out.println("====2.Selecting Partial Object====== ");

query = session.createQuery("Select b.accname, b.balance from BankBo b where b.accno=?");

query.setParameter(0, new Integer(127));

list = query.list();

it = list.iterator();

while (it.hasNext()) {

Object o[] = (Object[]) it.next();

System.out.println("Name : " + o[0]);

System.out.println("Balance : " + o[1]);

}

====1.Selecting Complete Object======

ACC No : 121

Name : Satya

Balance : 589000.0

------------------------

ACC No : 127

Name : Surya

Balance : 56000.0

====2.Selecting Partial Object======

Name : Surya

Balance : 56000.0

2. HQL Update/Delete Query Example

while working with DML operations in HQL we have to call executeUpdate(); to execute the query, which will returns one integer value after the execution it will tells the count of effected rows.

package hql;

import org.hibernate.Query;

import org.hibernate.SessionFactory;

import org.hibernate.Transaction;

import org.hibernate.cfg.Configuration;

import org.hibernate.classic.Session;

public class HQLUpdateDelete {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory factory = cfg.buildSessionFactory();

Session session = factory.openSession();

System.out.println("====== UPDATE OPERATION =========");

Transaction tx = session.beginTransaction();

Query query = session.createQuery("update BankBo b set b.balance =? where b.accno=?");

query.setParameter(0, new Double(0));

query.setParameter(1, new Integer(127));

int rs = query.executeUpdate();

tx.commit();

System.out.println(rs + " :Rows are Updated");

System.out.println("====== DELETE OPERATION =========");

tx = session.beginTransaction();

query = session.createQuery("delete from BankBo b where b.accno=?");

query.setParameter(0, new Integer(133));

rs = query.executeUpdate();

System.out.println(rs + " :Rows are Updated");

tx.commit();

session.close();

}

mysql> select * from bank;

+-------+---------+---------+

| accno | accname | balance |

+-------+---------+---------+

| 121 | Satya | 589000 |

| 127 | Surya | 0 |

+-------+---------+---------+

2 rows in set (0.00 sec)

3. HQL Insert Query Example

while writing the insert query, we need to select values from other table, we can't insert our own values manually. Because, HQL supports only the INSERT INTO......... SELECT......... ; it won't support INSERT INTO...........VALUES

Query query = session.createQuery("insert into Stock(stock_code, stock_name)" +

"select stock_code, stock_name from backup_stock");

int result = query.executeUpdate();

HQL with Aggregate functions

We may call avg(), min(), max() etc. aggregate functions by HQL. Let's see some common examples:

Example to get total salary of all the employees

Query q=session.createQuery("select sum(salary) from Emp");

List<Integer> list=q.list();

System.out.println(list.get(0));

Example to get maximum salary of employee

Query q=session.createQuery("select max(salary) from Emp");

Example to get minimum salary of employee

Query q=session.createQuery("select min(salary) from Emp");

Example to count total number of employee ID

Query q=session.createQuery("select count(id) from Emp");

Example to get average salary of each employees

Query q=session.createQuery("select avg(salary) from Emp");

Hibernate Criteria Query Language(HCQL) ==========================================

Criteria is nothing but a Condition. CQL is used to apply conditions on SELECT Queries. The Criteria interface provides methods to apply criteria on SELECT queries.

Criteria Interface

The Criteria interface provides many methods to specify criteria. The object of Criteria can be obtained by calling the createCriteria() method of Session interface

**public Criteria createCriteria(Class c) **

commonly used methods of Criteria interface are as follows:

public Criteria add(Criterion c) is used to add restrictions.
public Criteria addOrder(Order o) specifies ordering.
public Criteria setFirstResult(int firstResult) specifies the first number of record to be retreived.
public Criteria setMaxResult(int totalResult) specifies the total number of records to be retreived.
public List list() returns list containing object.
public Criteria setProjection(Projection projection) specifies the projection

Working with Criteria Query Language

[Example Criteria]{.underline}

Criteria crit = session.createCriteria(Products.class);

Criterion c1=Restrictions.gt("price", new Integer(12000));

//price is our pojo class variable

crit.add(c1); // adding criterion object to criteria class object

List l = crit.list(); // executing criteria query

If we want to put, we need to create one Criterion Interface object and we need to add() this object to Criteria Class object
In order to get Criterion object, we need to use Restrictions class. Restrictions is the factory for producing Criterion objects
In Restrictions class, we have all static methods and each method of this class returns Criterion object

REMEMBER: CQL is only used on SELECT Queries

Example: Get the details from bank table where balance>3000.

Table : Bank

mysql> select * from bank;

+-------+---------+---------+

| accno | accname | balance |

+-------+---------+---------+

| 101 | Satya | 2000 |

| 102 | Surya | 3000 |

| 103 | Ravi | 1000 |

| 104 | Rakesh | 4000 |

| 105 | CHANDU | 5000 |

+-------+---------+---------+

5 rows in set (0.00 sec)

[BankBo.java]{.underline}

package hql;

public class BankBo {

private int accno;

private String accname;

private double balance;

public int getAccno() {

return accno;

}

public void setAccno(int accno) {

this.accno = accno;

}

public String getAccname() {

return accname;

}

public void setAccname(String accname) {

this.accname = accname;

}

public double getBalance() {

return balance;

}

public void setBalance(double balance) {

this.balance = balance;

}

[BankBo.hbm.xml]{.underline}

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping SYSTEM "hibernate-mapping-3.0.dtd">

<hibernate-mapping>

</class>

</hibernate-mapping>

[hibernate.cfg.xml]{.underline}

<hibernate-configuration>

<session-factory>

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="hibernate.connection.url">jdbc:mysql://[localhost]{.underline}:3306/[smlcodes]{.underline}</property>

<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

</session-factory>

</hibernate-configuration>

package cql;

import java.util.Iterator;

import java.util.List;

import org.hibernate.*;

import hql.BankBo;

public class CriteriaDemo {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory factory = cfg.buildSessionFactory();

Session session = factory.openSession();

Criteria criteria = session.createCriteria(BankBo.class);

Criterion cn = Restrictions.gt("balance", new Double(3000));

criteria.add(cn);

[List]{.underline} list = criteria.list();

System.out.println("List Size : " + list.size());

[Iterator]{.underline} it = list.iterator();

while (it.hasNext()) {

BankBo bo = (BankBo) it.next();

System.out.println(bo.getAccno() + ", " + bo.getAccname() + ", " + bo.getBalance());

}

session.close();

factory.close();

}

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).

log4j:WARN Please initialize the log4j system properly.

Hibernate: select this_.accno as accno0_0_, this_.accname as accname0_0_, this_.balance as balance0_0_ from bank this_ where this_.balance>?

List Size : 2

104, Rakesh, 4000.0

105, CHANDU, 5000.0

Example: Adding ORDERBY Conditions to Criteria

If we want to add some sorting order for the objects, we need to add an Order class object to the Criteria class object by calling **addOrder() method.**In Order class, we have asc() and dsc() for getting an objects in required order.

public class CriteriaOrderExample {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory factory = cfg.buildSessionFactory();

Session session = factory.openSession();

Criteria criteria = session.createCriteria(BankBo.class);

Criterion cn = Restrictions.gt("balance", new Double(2000));

criteria.add(cn);

criteria.addOrder(Order.asc("balance"));

[List]{.underline} list = criteria.list();

[Iterator]{.underline} it = list.iterator();

while (it.hasNext()) {

BankBo bo = (BankBo) it.next();

System.out.println(bo.getAccno() + ", "+ bo.getBalance());

}

session.close();

factory.close();

}

log4j:WARN No appenders could be found for logger

102, 3000.0

104, 4000.0

105, 5000.0

hibernate will select the records (rows) from BankBo table and stores them into a ResultSet and then converts each row data of resultset into a POJO class object basing on our field type, then all these objects into a list according to the order you have given

Example: Adding multiple conditions

If we want to put more conditions on the data (multiple conditions) then we can use and method, or method given by the Restrictions class

crit.add(Restrictions.and(Restrictions.like("accname","%satya%"),

Restrictions.eq("price",new Integer(12000))));

List l=crit.list();

Iterator it = l.iterator();

Like this we can add any number of conditions

Hibernate Projections

In criteria, we are able to load complete object only, to load the partial objects (Selected Columns only) we need to use projections.

Projection is an Interface, Projections is an class for producing projection objects.
In Projections class, we have all static methods and each method of this class returns Projection interface object.
If we want to add a Projection object to Criteria then we need to call a method setProjection()

Projections Syntax

while adding projection object to criteria, it is possible to add one object at a time. It means if we add 2nd projection object then this 2nd one will override the first one (first one won't be work), so at a time we can only one projection object to criteria object.

Using criteria, if we want to load partial object from the database, then we need to create a projection object for property that is to be loaded from the database

[Example:]{.underline}

Criteria crit = session.createCriteria(Products.class);

crit.setProjection(Projections.proparty("proName"));

List l=crit.list();

Iterator it=l.iterator();

while(it.hasNext())

{

String s = (String)it.next();

// ---- print -----

}

Example 1: Load Single Column using Projections

In below example we are using same configuration files and BanlBo.java as above examples

public class ProjectionsDemo {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory factory = cfg.buildSessionFactory();

Session session = factory.openSession();

Criteria criteria = session.createCriteria(BankBo.class);

Criterion cn = Restrictions.gt("balance", new Double(2000));

criteria.add(cn);

criteria.setProjection(Projections.property("balance"));

[List]{.underline} list = criteria.list();

System.out.println("List Size : " + list.size());

[Iterator]{.underline} it = list.iterator();

while (it.hasNext()) {

Double bal = (Double) it.next();

System.out.println("Balance : " + bal);

}

session.close();

factory.close();

}

Hibernate: select this_.balance as y0_ from bank this_ where this_.balance>?

List Size : 3

Balance : 3000.0

Balance : 4000.0

Balance : 5000.0

Example 2: Load Multiple Columns using Projections

If we want to load partial object, with multiple columns using criteria then we need to create the ProjectionList with the multiple properties and then we need to add that Projectionist to the criteria.

public class ProjectionsMultipleColumns {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory factory = cfg.buildSessionFactory();

Session session = factory.openSession();

Criteria criteria = session.createCriteria(BankBo.class);

Criterion cn = Restrictions.gt("balance", new Double(2000));

criteria.add(cn);

ProjectionList projectionList = Projections.projectionList();

projectionList.add(Projections.property("accname"));

**projectionList.add(Projections.property("balance")); **

**criteria.setProjection(projectionList); **

[List]{.underline} list = criteria.list();

[Iterator]{.underline} it = list.iterator();

while (it.hasNext()) {

Object[] o = (Object[]) it.next();

System.out.println(o[0]+" : " +o[1]);

}

session.close();

factory.close();

}

Hibernate: select this_.accname as y0_, this_.balance as y1_ from bank this_ where this_.balance>?

Surya : 3000.0

Rakesh : 4000.0

CHANDU : 5000.0

Difference between HQL and CQL

HQL (Hibernate Query Language) CQL (Criteria Query Language)

We can perform **both select and non-select operations ** Criteria is only for selecting the data, we cannot perform non-select operations suitable for executing Static Queries suitable for executing Dynamic Queries Takes less time to execute Takes more time to execute

Native SQL Queries =====================

HQL or Criteria queries able to execute almost any SQL query you want. However, many developers are complaint about the Hibernate's generated SQL statement is slow and more prefer to generated their own SQL (native SQL) statement.

Hibernate provide a createSQLQuery() method to let you call your native SQL statement directly. Your application will create a native SQL query from the session with the createSQLQuery() method on the Session interface.:

public SQLQuery createSQLQuery(String sqlString) throws HibernateException

By using Native SQL, we can perform both SELECT & NON- SELECT operations on the data
We can use the database specific keywords (commands), to get the data from the database
The main drawback of Native SQL is it makes the hibernate application as database dependent.

Working with Native SQL Queries

Even though we are selecting complete objects from the database we need to type cast into Object[] array only, not into our pojo class type, because we are giving direct table, column names in the Native SQL Query so it doesn't know our class name

SQLQuery qry = session.createSQLQuery("select * from EMPLOYEE");

// Here EMPLOYEE is the table in the database...

List l = qry.list();

Iterator it = l.iterator();

while(it.hasNext())

{

Object row[] = (Object[])it.next();

--- -------

}

In the above code, we typecast into the object[] , if we want to type cast into our POJO class , then we need to go with entityQuery concept. to make the query as an entityQuery, we need to call addEntity() method

//We are letting hibernate to know our pojo class too

SQLQuery q=session.createSQLQuery("select *from EMPLOYEE").addEntity(EmployeeBo.class);

List l = q.list();

Iterator it = l.iterator();

while(it.hasNext())

{

EmployeeBo s = (EmployeeBo)it.next();

--- -------

}

Example

public class NativeSqlDemo {

public static void main(String[] args) {

// 1.Load Configuration

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

// 2.Create Session

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

System.out.println("1.Simple Native SQL\n ========================");

SQLQuery query1 = session.createSQLQuery("select *from EMPLOYEE");

[List]{.underline} list1 = query1.list();

[Iterator]{.underline} it1 = list1.iterator();

while (it1.hasNext()) {

Object[] ob = (Object[]) it1.next();

System.out.println(ob[0] + ", " + ob[1] + ", " + ob[2]);

}

System.out.println("2.Native SQL with entityQuery\n ==========");

SQLQuery query2 = session.createSQLQuery("select *from EMPLOYEE");

query2.addEntity(EmployeeBo.class);

[List]{.underline} list2 = query2.list();

[Iterator]{.underline} it2 = list2.iterator();

while (it2.hasNext()) {

EmployeeBo bo = (EmployeeBo) it2.next();

System.out.println(bo.getEid() + ", " + bo.getName() + ", " + bo.getAddress());

}

session.close();

sf.close();

}

1.Simple Native SQL

========================

1, SATYA, VIJAYAWADA

2, SURYA, HYDERABAD

2.Native SQL with entityQuery

========================

1, SATYA, VIJAYAWADA

2, SURYA, HYDERABAD

Named Queries =================

if we want to execute the same queries for multiple times in our program then we can use the Named Queries mechanism

In this Named Queries concept, we use some name for the query configuration, and that name will be used whenever the same query is required to execute
If you want to create Named Query, in hibernate mapping file we need to configure a query by putting some name for it.
In HQL, we need to use <query name="query_name"> to configure query

<query name="bankHQLQuery">

<![CDATA[from BankBo b where b.balance>:bal ]]>

</query>

In Native SQL, we need to use <sql-queryname="query_name"> to configure query

<sql-query name="bankNativeQuery">

select * from Employee

</sql-query>

In our main program, we need to use getNamedQuery() given by session interface, for getting the Query reference and we need to execute that query by calling list()

Query qry = session.getNamedQuery("Name given in hib-mapping-xml");

qry.setParameter("bal",new Integer(3000));

List l = qry.list();

Example 1 : HQL Named Query Example

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration SYSTEM

"hibernate-configuration-3.0.dtd">

<hibernate-configuration>

<session-factory>

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="hibernate.connection.url">jdbc:mysql://[localhost]{.underline}:3306/[smlcodes]{.underline}</property>

<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

<property name="hbm2ddl.auto">update</property>

</session-factory>

</hibernate-configuration>

[BankBo.java]{.underline}

public class BankBo {

private int accno;

private String accname;

private double balance;

//Setters & getters

[BankBo.hbm.xml]{.underline}

<hibernate-mapping>

</class>

<![CDATA[from hql.BankBo b where b.balance>:bal ]]>

</query>

</hibernate-mapping>

[HQLNamedQuery.java]{.underline}

package namedQuery;

public class HQLNamedQuery {

public static void main(String[] args) {

// 1.Load Configuration

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

// 2.Create Session

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

System.out.println("HQL-NamedQuery Example\n----------");

Query qry = session.getNamedQuery("bankHQLQuery");

qry.setParameter("bal", new Double(3000));

[List]{.underline} list = qry.list();

[Iterator]{.underline} it = list.iterator();

while (it.hasNext()) {

BankBo bo = (BankBo) it.next();

System.out.println(bo.getAccname() + ", " + bo.getBalance());

}

session.close();

sf.close();

}

HQL-NamedQuery Example

------

Hibernate: select bankbo0_.accno as accno1_, bankbo0_.accname as accname1_, bankbo0_.balance as balance1_ from bank bankbo0_ where bankbo0_.balance>?

Rakesh, 4000.0

CHANDU, 5000.0

Example 2 : Native SQL Named Query Example

[EmployeeBo.java]{.underline}

package bo;

public class EmployeeBo {

private int eid;

private String name;

private String address;

//Setters & getters

}

[EmployeeBo.hbm.xml]{.underline}

<hibernate-mapping>

</id>

</class>

<sql-query name="employeeNativeQuery">

select * from Employee

</sql-query>

</hibernate-mapping>

[NamedQueryDemo.java]{.underline}

package namedQuery;

public class NamedQueryDemo {

public static void main(String[] args) {

// 1.Load Configuration

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

// 2.Create Session

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

Query qry = session.getNamedQuery("employeeNativeQuery");

[List]{.underline} list = qry.list();

[Iterator]{.underline} it = list.iterator();

while (it.hasNext()) {

Object o[] = (Object[]) it.next();

System.out.println(o[0] + ", " + o[1] + ", " + o[2]);

}

session.close();

sf.close();

}

HQL-NamedQuery Example-------------------------

Hibernate: select bankbo0_.accno as accno1_, bankbo0_.accname as accname1_, bankbo0_.balance as balance1_ from bank bankbo0_ where bankbo0_.balance>?

Rakesh, 4000.0

CHANDU, 5000.0

Hibernate Relationships ===========================

In JAVA we have three types of relationships

IS -- A
HAS --A
Uses -- A

[1.Is-a]{.underline} relationship is one in which data members of one class is obtained into another class through the concept of inheritance.

class B{

}

public class A extends B{

}

[2.Has-a]{.underline} relationship is one in which an object of one class is created as a data member in another class.

{width="3.15625in" height="1.6145833333333333in"}

[3.Uses-a]{.underline} relationship is one in which an Object of one class is created inside a method of another class.

{width="2.5625in" height="1.6770833333333333in"}

NOTE: But in Database We don't have is-a,has-a,uses-a relationships like in java

Relationships in Hibernate

In database we don't have above mentioned relationships, but we can form the relationship between database tables by using Primary Key (P.K), Foreign Key (F.K). We can only form HAS-A relationship in hibernate.

We have four types of relationships

One-To-One (P.K → P.K, F.K(Unique) → P.K)
One-To-Many (P.K → F.K)
Many-To-One (F.K → P.K)
Many-To-Many (Table1 → LinkTable → Table2)

If you see above replations One→P.K, Many→F.K. Just kidding

Mapping Directions

Each relationship can be achived in two directions

1.Unidirectional relationship refers to the case when relationship between two objects can be accessed by one way only. i.e. from Library we can access books, from book we can't access Library, not vice versa.

class Book{

Long bookId;

String bookName;

[...........]{.underline}

}

class Library{

Long libraryId;

String libraryName;

[Set]{.underline}<Book> bookSet;

}

2.Bidirectional relationship refers to the case when relationship between two objects can be accessed both ways. i.e. From Library we can access books, from book we can access Library, vice versa.

class Book{

Long bookId;

String bookName;

Library library;

[...........]{.underline}

}

class Library {

Long libraryId;

String libraryName;

[Set]{.underline}<Book> bookSet;

}

Relationship Explanation Example

One-To-One Each record in one table is related to exactly one record in the second table and vice versa. The other side could also be a zero record. A car has only one engine. One-To-Many (or) Many-To-One Each record in one table is related to zero or more records in the second table. A movie has many actors (one-to-many); an actor can act in many movies (manyto-one). Many-To-Many Each record in either of the tables is related to zero or more records in the other table Each student can enroll in multiple courses, and each course can have manystudents registered.

REMEMEBER: Object means one row in hibernate terminology

1.One-to-One Relationship Mapping Example

Using our Car and Engine example, we develop a one-to-one association. There are two ways of establishing a one-to-one association, using a primary key using a foreign key.

Example: OneToOne Mapping (BiDirectional)

CREATE TABLE CAR (

CAR_ID int(10) NOT NULL,

NAME varchar(20) DEFAULT NULL,

COLOR varchar(20) DEFAULT NULL,

PRIMARY KEY (CAR_ID));

CREATE TABLE ENGINE (

CAR_ID int(10) NOT NULL,

SIZE varchar(20) DEFAULT NULL,

MODEL varchar(20) DEFAULT NULL,

PRIMARY KEY (CAR_ID),

FOREIGN KEY (CAR_ID) REFERENCES car (CAR_ID));

CAR table with a CAR_ID as the primary key.
ENGINE table, primary key is a CAR_ID.
ENGINE table has a foreign key constraint pointing to the primary key of the CAR table. So, an engine will always be created with the same id as that of a car. Thus, we say both tables share the same primary key.

[Car.java]{.underline}

package onetoone;

public class Car {

private int id;

private String name;

private String color;

private Engine engine;

//Setters & Getters

}

[Engine.java]{.underline}

package onetoone;

public class Engine {

private int id = 0;

private String model = null;

private String size = null;

// this engine is fitted to a car

private Car car = null;

//Setters & Getters

}

[Car.hbm.xml]{.underline}

<hibernate-mapping package="onetoone">

</id>

<one-to-one name="engine" class="Engine" cascade="all" />

</class>

</hibernate-mapping>

[Engine.hbm.xml]{.underline}

<hibernate-mapping package="onetoone">

</generator>

</id>

<one-to-one name="car" class="Car" constrained="true" />

</class>

</hibernate-mapping>

[hibernate.cfg.xml]{.underline}

<hibernate-configuration>

<session-factory>

. . . . .

. . . . .

</session-factory>

</hibernate-configuration>

[OneToOneTest.java]{.underline}

package onetoone;

public class OneToOneTest {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

Car car = new Car();

// Remember, we are using application generator for [ids]{.underline}

car.setId(1);

car.setName("SWIFT");

car.setColor("BLUE");

// Next, create an instance of engine and set values.

// Note: you are not setting the id!

Engine engine = new Engine();

engine.setModel("2009");

engine.setSize("85KG");

// Now we associate them together using the setter on the car

car.setEngine(engine);

engine.setCar(car);

// Lastly, we are persisting them

Transaction tx = session.beginTransaction();

session.save(car);

session.save(engine);

tx.commit();

System.out.println("Succuess");

}

mysql> select * from car;

+--------+--------------------+-------+

| CAR_ID | NAME | COLOR |

+--------+--------------------+-------+

| 1 | SWIFT | BLUE |

+--------+--------------------+-------+

2 rows in set (0.00 sec)

mysql> select * from engine;

+--------+------------+-------+

| CAR_ID | size | MODEL |

+--------+------------+-------+

| 1 | 85KG | 2009 |

+--------+------------+-------+

2.One-to-Many / Many-to-One Relationship

To achieve one-to-many between two pojo classes in the hibernate, then the following two changes are required

In the parent pojo class, we need to take a collection property, the collection can be either Set, List, Map .

public class Movie {

private int mid;

private String title;

private Set<Actor> actors;

//Setters & Getters

}

In the mapping file of that parent pojo class, we need to configure the collection

<set name="actors" table="actor" cascade="all">

<key column="mid" not-null="true" />

<one-to-many class="Actor" />

</set>

In this example we are taking Movie & Actor table, the relation between them is "one" movie consists of "one or more (i.e., many)" actors

CREATE TABLE `movie` (

`mid` INT(10) NOT NULL AUTO_INCREMENT,

`title` VARCHAR(10) NULL DEFAULT NULL,

PRIMARY KEY (`mid`)

)

CREATE TABLE `actor` (

`actorid` INT(10) NOT NULL AUTO_INCREMENT,

`name` VARCHAR(20) NULL DEFAULT NULL,

`age` INT(10) NULL DEFAULT NULL,

`mid` INT(10) NULL DEFAULT NULL,

PRIMARY KEY (`actorid`),

INDEX `FK585A9F550821B2A` (`mid`),

INDEX `FK585A9F578674FF6` (`mid`),

CONSTRAINT `FK585A9F550821B2A` FOREIGN KEY (`mid`) REFERENCES `movie` (`mid`)

)

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="5.98584208223972in" height="1.069242125984252in"}

[Actor.java]{.underline}

package onetomany;

public class Actor {

private int actorid;

private String actorname;

private int age;

//Setters & getters

}

[Movie.java]{.underline}

package onetomany;

public class Movie {

private int mid;

private String title;

private Set<Actor> actors;

//Setters & Getters

}

[Actor.hbm.xml]{.underline}

<hibernate-mapping package="onetomany">

</id>

</class>

</hibernate-mapping>

[Movie.hbm.xml]{.underline}

<hibernate-mapping package="onetomany">

</id>

<one-to-many class="Actor" />

</set>

</class>

</hibernate-mapping>

In order to transfer operations on parent object to child object we need to add cascade attribute
By default, cascade value is none, it means even though relationship is exist, the operations we are doing on parent will not transfer to child.
In above xml, we used cascade =" all" means all operations at parent object will be transfer to child
Inthe mapping file, we need to use <key /> element to configure foregin key column name, in this example "mid" is foreign key
<one-to-many> is child class with which relation been done, in our example** Actor** is the child class

[OneToManyTest.java]{.underline}

package onetomany;

import java.util.HashSet;

import java.util.Set;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.Transaction;

import org.hibernate.cfg.Configuration;

public class OneToManyTest {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

Actor amir = new Actor();

amir.setActorname("AMIR KHAN");

amir.setAge(42);

amir.setActorid(101);

Actor madhav = new Actor();

madhav.setActorname("R. MADHAVAN");

madhav.setAge(36);

madhav.setActorid(102);

Actor kareena = new Actor();

kareena.setActorname("KAREENA KAPOOR");

kareena.setAge(31);

kareena.setActorid(103);

Set<Actor> actors =new HashSet<Actor>();

actors.add(amir);

actors.add(madhav);

actors.add(kareena);

Movie movie = new Movie();

movie.setTitle("3 IDIOTS");

movie.setActors(actors);

movie.setMid(501);

Transaction tx = session.beginTransaction();

session.save(movie);

tx.commit();

System.out.println("Succuess");

}

3.Many to Many Relationship

Applying many to many relationships between two pojo class objects is nothing but applying one to many relationships on both sides, which tends to Bi-Directional i mean many to many.

when ever we are applying many to many relationships between two pojo class objects**, on both sides we need a collection property **
While applying many to many relationships between pojo classes, a mediator table is mandatory in the database, to store primary key as foreign key both sides, we call this table as Join table

In the example of Student and Course, the relationship can be many-to-many: a student can take many courses, while a course may consist of many students

CREATE TABLE `course` (

`courseId` INT(11) NOT NULL AUTO_INCREMENT,

`courseName` VARCHAR(50) NULL DEFAULT NULL,

PRIMARY KEY (`courseId`)

)

CREATE TABLE `student` (

`studentId` INT(11) NOT NULL AUTO_INCREMENT,

`studentName` VARCHAR(50) NULL DEFAULT NULL,

PRIMARY KEY (`studentId`)

)

// mediator table

CREATE TABLE `student_course` (

`COURSE_ID` INT(10) NOT NULL,

`STUDENT_ID` INT(10) NOT NULL,

PRIMARY KEY (`COURSE_ID`, `STUDENT_ID`),

INDEX `FKCB6FBEBFAD895D0F` (`COURSE_ID`),

INDEX `FKCB6FBEBF88820545` (`STUDENT_ID`),

CONSTRAINT `fk_c_id` FOREIGN KEY (`COURSE_ID`) REFERENCES `course` (`courseId`),

CONSTRAINT `fk_s_id` FOREIGN KEY (`STUDENT_ID`) REFERENCES `student` (`studentId`)

)

Course.java

package manytomany;

public class Course {

private int courseId;

private String courseName;

private Set<Student> students;

//Setters & Getters

}

Student.java

package manytomany;

public class Student {

private int studentId;

private String studentName;

private Set<Course> courses;

//Setters & Getters

}

[Course.hbm.xml]{.underline}

<hibernate-mapping package="manytomany">

</id>

<set name="students" table="STUDENT_COURSE" inverse="true"

cascade="all">

<many-to-many column="STUDENT_ID" class="Student" />

</set>

</class>

</hibernate-mapping>

[Student.hbm.xml]{.underline}

<hibernate-mapping package="manytomany">

</id>

<many-to-many column="COURSE_ID" class="Course" />

</set>

</class>

</hibernate-mapping>

package manytomany;

public class ManyToManyTest {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

Student s1 = new Student();

s1.setStudentId(101);

s1.setStudentName("SATYA");

Student s2 = new Student();

s2.setStudentId(102);

s2.setStudentName("ARJUN");

Course c1 = new Course();

c1.setCourseId(301);

c1.setCourseName("JAVA");

Course c2 = new Course();

c2.setCourseId(302);

c2.setCourseName(".NET");

Set<Student> students = new HashSet<Student>();

students.add(s1);

students.add(s2);

c1.setStudents(students);

c2.setStudents(students);

Set<Course> courses = new HashSet<Course>();

courses.add(c1);

courses.add(c2);

s1.setCourses(courses);

s2.setCourses(courses);

Transaction tx = session.beginTransaction();

session.save(s1);

session.save(s2);

tx.commit();

System.out.println("Succuess");

}

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="6.5in" height="0.9322036307961504in"}

Cascade Attribute In Hibernate

Cascade attribute is mandatory, whenever we apply relationship between objects, cascade attribute transfers operations done on one object onto its related child objects. default value of cascade ="none" means no operations will be transfers to the child class

If we write cascade = "all" then changes like insert, delete, update at parent object will be effected to child object.

Cascade having following values

none (default), save, update, save-update, delete, all, all-delete-orphan

Hibernate Cache ===================

Every fresh session having its own cache memory, Caching is a mechanism for storing the loaded objects into a cache memory. The advantage of cache mechanism is, whenever again we want to load the same object from the database then instead of hitting the database once again, it loads from the local cache memory only**, so that the no. of round trips between an application and a database server got decreased**. It means caching mechanism increases the performance of the application.

In hibernate we have two levels of caching

**First Level Cache (**Session Cache)
Second Level Cache (Session Factory Cache/ JVM Level Cache)

1.First Level Cache

By default, for each hibernate application, the first level cache is automatically enabled. We can't Enable/Disable first level cache
the first level cache is associated with the session object and scope of the cache is limited to one session only
When we load an object for the first time from the database then the object will be loaded from the database and the loaded object will be stored in the cache memory maintained by that session object
If we load the same object once again, with in the same session, then the object will be loaded from the local cache memory not from the database
If we load the same object by opening other session, then again the object will load from the database and the loaded object will be stored in the cache memory maintained by this new session

[Example:]{.underline}

Session session = factory.openSession();

Object ob1 = session.get(Actor.class, new Integer(101)); //1

Object ob2 = session.get(Actor.class, new Integer(101));//2

Object ob3 = session.get(Actor.class, new Integer(101));//3

session.close();//4

Session ses2 = factory.openSession();

Object ob5 = ses2.get(Actor.class, new Integer(101));//5

1, We are loaded object with id 101, now it will load the object from the database only as its the first time, and keeps this object in the session cache

2,3 i tried to load the same object 2 times, but here the object will be loaded from the stored cache only not from the database, as we are in the same session

4, we close the first session, so the cache memory related this session also will be destroyed

5, again i created one new session and loaded the same object with id 101, but this time hibernate will loads the object from the database

if we want to remove the objects that are stored in the cache memory, then we need to call either evict() or clear() methods

2.Second Level Cache

Whenever we are loading any object from the database, then hibernate verify whether that object is available in the local cache(first level cache) memory of that particular session, if not available then hibernate verify whether the object is available in global cache(second level cache), if not available then hibernate will hit the database and loads the object from there, and then first stores in the local cache of the session , then in the global cache

SessionFactory holds the second level cache data. It is global for all the session objects and not enabled by default.

Different vendors have provided the implementation of Second Level Cache

EH Cache
OS Cache
Swarm Cache
JBoss Cache

To enable second level cache in the hibernate, then the following 3 changes are required

Add provider class in hibernate configuration file

<property name="hibernate.cache.provider_class">

org.hibernate.cache.EhCacheProvider

</property>

Configure cache element for a class in hibernate mapping file

<cache usage="read-only" />

read-only: caching will work for read only operation.
nonstrict-read-write: caching will work for read and write but one at a time.
read-write: caching will work for read and write, can be used simultaneously.
transactional: caching will work for transaction.

create xml file called ehcache.xml and place where you have mapping and configuration xml's

[Example:]{.underline}

public class Employee {

private int eid;

private String name;

private String address;

//Setters & Getteers

}

[Employee.hbm.xml]{.underline}

<hibernate-mapping package="cache">

</id>

</class>

</hibernate-mapping>

[ehcache.xml]{.underline}

<?xml version="1.0"?>

<defaultCache maxElementsInMemory="100" eternal="false"

timeToIdleSeconds="120" timeToLiveSeconds="200" />

<cache name="cache.Employee" maxElementsInMemory="100"

eternal="false" timeToIdleSeconds="5" timeToLiveSeconds="200" />

</ehcache>

[hibernate.cfg.xml]{.underline}

<hibernate-configuration>

<session-factory>

<property> Driver Class, URL, Username, password, etc </property>

<property name="cache.provider_class">org.hibernate.cache.EhCacheProvider</property>

</session-factory>

</hibernate-configuration>

[CacheDemo.java]{.underline}

package cache;

import org.hibernate.*;

import org.hibernate.cfg.*;

public class CacheDemo {

public static void main(String[] args) {

//1.Load Configuration

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

//2.Create Session

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

//3.Perform Operations

Object ob = session.load(Employee.class, new Integer(1));

Employee bo = (Employee) ob;

System.out.println("SELECTED DATA\n ================");

System.out.println("SNO : "+bo.getEid());

System.out.println("NAME : "+bo.getName());

System.out.println("ADDRESS : "+bo.getAddress());

}

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Hibernate with Annotations ==============================

The EJB 3 standard annotations are contained in the javax.persistence package, so we import this package.

Use annotations in POJO classes. These classes are called Entity Bean Classes
No need of xml files
We use AnnotationConfiguartion class instead of Configuration class

Configuration cfg = new AnnotationConfiguartion ();

From Hibernate 4.x version Configuration is enough for both annotation and xml configuration
We have to configure POJO class in hbm.xml

<mapping class="bean.Student">

Commonly used Annotations in Hibernate

1.@Entity

Annotation marks this class as an entity.
We have to place this annotation at the top of class

**2.@Table **

Specifies Table to be connect with this class. If you don't use @Table annotation, hibernate will use the class name as the table name by default.
We have to place this annotation at the top of class.

3.@Id

Every table has a primary key; we can make the data member as Primary Key using @Id annotation.

4.@GeneratedValue

It will generate the Primary Key/ ID values automatically

5.@Column

This Annotation specifies the details of the column for this property or field.
If @Column is not specified, property name will be used as the column name by default.

6. **@Transient **

We can declare the data members which are not have columns in database table

7.@ManyToMany

Cascade: Marks this field as the owning side of the many-to-many relationship and cascade modifier specifies which operations should cascade to the inverse side of relationship
mappedBy: This modifier holds the field which specifies the inverse side of the relationship

8.@JoinTable

Name: For holding this many-to-many relationship, maps this field with an intermediary database join table specified by name modifier
joinColumns: Identifies the owning side of columns which are necessary to identify a unique owning object
inverseJoinColumns: Identifies the inverse (target) side of columns which are necessary to identify a unique target object

9.@JoinColumn

Maps a join column specified by the name identifier to the relationship table specified by @JoinTable

Example: CURD operations using Annotations

CREATE TABLE `studenttable` (

`sno` INT(11) NOT NULL AUTO_INCREMENT,

`name` VARCHAR(50) NULL DEFAULT NULL,

`address` VARCHAR(50) NULL DEFAULT NULL,

PRIMARY KEY (`sno`)

)

[StudentBo.java]{.underline}

package annotations;

@Entity

@Table(name="studenttable")

public class StudentBo {

@Id

@Column(name="sno")

@GeneratedValue(strategy=GenerationType.AUTO)

private int sno; //PRIMARY_KEY

@Column(name="name")

private String name;

@Column //By default it will take [datamember]{.underline} name

private String address;

@Transient

private String iamnotindatabase;

//This column not their in [db]{.underline}

public int getSno() {

return sno;

}

public void setSno(int sno) {

this.sno = sno;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getAddress() {

return address;

}

public void setAddress(String address) {

this.address = address;

}

public StudentBo( String name, String address) {

super();

this.name = name;

this.address = address;

}

public StudentBo() {

super();

}

<hibernate-configuration>

<session-factory>

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="hibernate.connection.url">jdbc:mysql://[localhost]{.underline}:3306/[smlcodes]{.underline}</property>

<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

<property name="hbm2ddl.auto">update</property>

<property name="cache.provider_class">org.hibernate.cache.EhCacheProvider</property>

</session-factory>

</hibernate-configuration>

[AnnotationExample.java]{.underline}

package annotations;

public class AnnotationExample {

public static void main(String[] args) {

Configuration cfg = new AnnotationConfiguration();

cfg.configure("hibernate.cfg.xml");

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

Transaction tx = session.beginTransaction();

System.out.println("1.Save Operation");

System.out.println("===============================");

StudentBo e1 = new StudentBo("SATYA", "HYD");

StudentBo e2 = new StudentBo("RAM", "BANGLORE");

StudentBo e3 = new StudentBo("KIRAN", "MUMBAI");

session.save(e1);

session.save(e2);

session.save(e3);

System.out.println("2.Select Operation");

System.out.println("===============================");

List<StudentBo> ob = [session.createQuery("FROM StudentBo").list()]{.underline};

for (StudentBo e : ob) {

System.out.println(e.getSno()+", "+e.getName()+", "+e.getAddress());

}

tx.commit();

session.close();

sf.close();

}

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.annotations.Version).

log4j:WARN Please initialize the log4j system properly.

1.Save Operation

===============================

Hibernate: insert into studenttable (name, address) values (?, ?)

2.Select Operation

===============================

Hibernate: select studentbo0_.sno as sno0_, studentbo0_.name as name0_, studentbo0_.address as address0_ from studenttable studentbo0_

1, SATYA, HYD

2, RAM, BANGLORE

3, KIRAN, MUMBAI

Mappings using Annotations

1.one-to-one mapping using Annotations

Car.java

package annotations.onetoone;

@Entity

@Table(name="car")

public class Car {

@Id

@Column(name="CAR_ID")

private int id;

@Column(name="NAME")

private String name;

@Column(name="COLOR")

private String color;

//Setters & Getters

}

Engine.java

package annotations.onetoone;

@Entity

@Table(name="engine")

public class Engine {

@Id

private int id = 0;

@Column

private String model = null;

@Column

private String size = null;

@OneToOne(targetEntity=Car.class,cascade=CascadeType.ALL)

@JoinColumn(name="CAR_ID",referencedColumnName="CAR_ID")

private Car car = null;

//Setters & Getters

}

OneToOneTest.java

package annotations.onetoone;

public class OneToOneTest {

public static void main(String[] args) {

Configuration cfg = new AnnotationConfiguration();

cfg.configure("hibernate.cfg.xml");

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

Car car = new Car();

car.setId(2);

car.setName("BENZ");

car.setColor("RED");

Engine engine = new Engine();

engine.setModel("2209");

engine.setSize("815KG");

engine.setCar(car);

Transaction tx = session.beginTransaction();

session.save(car);

session.save(engine);

tx.commit();

System.out.println("Succuess");

}

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="5.177083333333333in" height="1.0104166666666667in"}

2.one-to-many Mapping Using Annotations

Actor.java

package annotations.onetomany;

@Entity

@Table(name="actor")

public class Actor {

@Id

@Column

private int actorid;

@Column(name="name")

private String actorname;

@Column

private int age;

//Setters & Getters

}

Movie.java

package annotations.onetomany;

@Entity

@Table(name="movie")

public class Movie {

@Id

@Column

private int mid;

@Column

private String title;

@OneToMany(cascade = CascadeType.ALL)

@JoinColumn(name="mid",referencedColumnName="mid")

private Set<Actor> actors;

//Setters & Getters

}

OneToManyTest.java

package annotations.onetomany;

public class OneToManyTest {

public static void main(String[] args) {

Configuration cfg = new AnnotationConfiguration();

cfg.configure("hibernate.cfg.xml");

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

Actor amir = new Actor();

amir.setActorname("PRABAS");

amir.setAge(36);

amir.setActorid(106);

Actor madhav = new Actor();

madhav.setActorname("DAGGUBATI RANA");

madhav.setAge(31);

madhav.setActorid(107);

Actor kareena = new Actor();

kareena.setActorname("KATTAPPA");

kareena.setAge(61);

kareena.setActorid(108);

Set<Actor> actors =new HashSet<Actor>();

actors.add(amir);

actors.add(madhav);

actors.add(kareena);

Movie movie = new Movie();

movie.setTitle("BAAHUBALI");

movie.setActors(actors);

movie.setMid(502);

Transaction tx = session.beginTransaction();

session.save(movie);

tx.commit();

System.out.println("Succuess");

}

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="5.927083333333333in" height="1.2083333333333333in"}

3.Many-to-many Mapping Using Annotations

Course.java

package annotations.manytomany;

@Entity

@Table(name="course")

public class Course {

@Id

@Column

private int courseId;

@Column

private String courseName;

@ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)

@JoinTable(name = "student_course", joinColumns = {

@JoinColumn(name = "COURSE_ID", nullable = false, updatable = false) },

inverseJoinColumns = { @JoinColumn(name = "STUDENT_ID",

nullable = false, updatable = false) })

private Set<Student> students;

//Setters & Getters

}

Student.java

package annotations.manytomany;

@Entity

@Table(name="student")

public class Student {

@Id

@Column

private int studentId;

@Column

private String studentName;

@Column

@ManyToMany(mappedBy = "students")

private Set<Course> courses;

//Setters & Getters

}

ManyToMantTest.java

package annotations.manytomany;

public class ManyToManyTest {

public static void main(String[] args) {

Configuration cfg = new AnnotationConfiguration();

cfg.configure("hibernate.cfg.xml");

SessionFactory sf = cfg.buildSessionFactory();

Session session = sf.openSession();

Student s1 = new Student();

s1.setStudentId(105);

s1.setStudentName("SACHIN");

Student s2 = new Student();

s2.setStudentId(112);

s2.setStudentName("DHONI");

Course c1 = new Course();

c1.setCourseId(303);

c1.setCourseName("DEVOPS");

Course c2 = new Course();

c2.setCourseId(304);

c2.setCourseName("HACKING");

Set<Student> students = new HashSet<Student>();

students.add(s1);

students.add(s2);

c1.setStudents(students);

c2.setStudents(students);

Set<Course> courses = new HashSet<Course>();

courses.add(c1);

courses.add(c2);

s1.setCourses(courses);

s2.setCourses(courses);

//we have to save the Course object, because we defiend M2M in Course class only

Transaction tx = session.beginTransaction();

session.save(c1);

session.save(c2);

tx.commit();

System.out.println("Succuess");

}

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\12.png$ {width="6.5in" height="0.9083333333333333in"}

Errors & Solutions

org.hibernate.HibernateException: Could not parse configuration: hibernate.cfg.xml

It was failing because there was no internet connection / you are behind proxy. To solve this issues

Extract hibernate3.jar file find hibernate-mapping-3.0.dtd, hibernate-configuration-3.0.dtd files
Paste the above two files root folder of your project

In hibernate.cfg.xml change lines to

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration SYSTEM

"hibernate-configuration-3.0.dtd">

In <Class>.hbm.xml change lines to

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping SYSTEM

"hibernate-mapping-3.0.dtd">

References

$E:\Users\kaveti_s.ITLINFOSYS\Pictures\hibernate_tutorial_smlcodes_logo.png$ {width="3.9166666666666665in" height="3.340399168853893in"}

http://www.java4s.com/hibernate

Mappings: OReilly.Just.Hibernate.Jun.2014.ISBN.1449334377.pdf

Hibernate Interview Questions

############################## What are advantages of Hibernate?

Lazy Loading
Caching
You do not need to maintain JDBC code , Hibernate takes care of it.
You need to write less code
It provides high level object oriented API

############################## 1. What is caching?

Anything you can do to minimize traffic between a database and an application server is probably a good thing. In theory, an application ought to be able to maintain a cache containing data already loaded from the database, and only hit the database when information has to be updated. When the database is hit, the changes may invalidate the cache

############################## What is evict and close?

############################## What are some core interfaces of hibernate?

Configuration
SessionFactory
Session
Transaction
Query and Criteria interface

############################## [Difference between get() vs load() method in Hibernate? (detailed answer)]{.underline}

The key difference between get() and load() method is that

load() will throw an exception if an object with id passed to them is not found
get() will return null.

Another important difference is that load can return proxy without hitting the database unless required (when you access any attribute other than id) but get() always go to the database, so sometimes using load() can be faster than the get() method. It makes sense to use the load() method if you know the object exists but get() method if you are not sure about object's existence.

Parameter get load

Database retrieval It always hits the database It does not hit database If null If it does not get the object with id, it returns null If it does get the object with id, it throws ObjectNotFoundException Proxy It returns real object It returns proxy object Use If you are not sure if object with id exists or not, you can use get If you are sure about existence of object, you can use load

[What is the difference between save() and persist() method in Hibernate?]{.underline}

Serializable Object save() returns a Serializable object

void persist() method is void, so it doesn't return anything.

############################## What is the difference between and merge and update?

Use update() if you are sure that the session does not contain an already persistent instance with the same identifier, and merge() if you want to merge your modifications at any time without consideration of the state of the session.

############################## Different between cascade and inverse

Many Hibernate developers are confuse about the cascade option and inverse keyword. In some ways..they really look quite similar at the beginning, both are related with relationship.

############################## Cascade vs inverse

However, there is no relationship between cascade and inverse, both are totally different notions.

1. inverse

This is used to decide which side is the relationship owner to manage the relationship (insert or update of the foreign key column).

Example

In this example, the relationship owner is belong to stockDailyRecords (inverse=true).

<hibernate-mapping>

...

<key>

</key>

<one-to-many class="com.mkyong.common.StockDailyRecord" />

</set>

...

Copy

When you save or update the stock object

session.save(stock);

session.update(stock);

Copy

Hibernate will only insert or update the STOCK table, no update on the foreign key column. More detail example here...

2. cascade

In cascade, after one operation (save, update and delete) is done, it decide whether it need to call other operations (save, update and delete) on another entities which has relationship with each other.

Example

In this example, the cascade="save-update" is declare on stockDailyRecords.

<hibernate-mapping>

...

<set name="stockDailyRecords" table="stock_daily_record"

cascade="save-update" inverse="true">

<key>

</key>

<one-to-many class="com.mkyong.common.StockDailyRecord" />

</set>

...

Copy

When you save or update the stock object

session.save(stock);

session.update(stock);

Copy

It will inserted or updated the record into STOCK table and call another insert or update statement (cascade="save-update") on StockDailyRecord. More detail example here...

Conclusion

In short, the "inverse" is decide which side will update the foreign key, while "cascade" is decide what's the follow by operation should execute. Both are look quite similar in relationship, but it's totally two different things. Hibernate developers are worth to spend time to research on it, because misunderstand the concept or misuse it will bring serious performance or data integrity issue in your application.

[Does SessionFactory is thread-safe in Hibernate? (detailed answer)]{.underline}
SessionFactory is both Immutable and thread-safe and it has just one single instance in Hibernate application. It is used to create Session object and it also provide caching by storing SQL queries stored by multiple session. The second level cache is maintained at SessionFactory level.

***[Does Hibernate Session interface is thread-safe in Java? (detailed answer)
]{.underline}***No, Session object is not thread-safe in Hibernate and intended to be used with-in single thread in the application.

[What is difference between getCurrentSession() and openSession() in Hibernate?]{.underline}

[openSession()]{.underline} When you call SessionFactory.openSession, it always create new Session object afresh and give it to you. As session objects are not thread safe, you need to create one session object per request in multithreaded environment and one session per request in web applications too.

[getCurrentSession()]{.underline} When you call SessionFactory. getCurrentSession , it creates a new Session if not exists , else use same session which is in current hibernate context. It automatically flush and close session when transaction ends, so you do not need to do externally.If you are using hibernate in single threaded environment , you can use getCurrentSession, as it is faster in performance as compare to creating new session each time.

You need to add following property to hibernate.cfg.xml to use getCurrentSession method

<session-factory>

</session-factory>

If you do not configure above property, you will get error as below.

Exception in thread "main" org.hibernate.HibernateException: No CurrentSessionContext configured!

############################## Can you declare Entity(Bean) class as final in hibernate?

Yes, you can declare entity class as final but it is not considered as a good practice because hibernate uses proxy pattern for lazy initialisation, If you declare it as final then hibernate won't be able to create sub class and won't be able to use proxy pattern, so it will limit performance and improvement options.

############################## Does entity class in hibernate require no arg constructor?

Yes, Entity class in hibernate requires no arg constructor because Hibernate use reflection to create instance of entity class and it mandates no arg constructor in Entity class

############################## How do you log SQL queries issued by the Hibernate framework in Java application?

You can procedure the show_sql property to log SQL queries delivered by the Hibernate framework

############################## What is named SQL query in Hibernate?

Named queries are SQL queries which are defined in mapping document using <sql-query> tag and called using Session.getNamedQuery() method.

<sql-query name="findStudentByRollNumber">

<!--[CDATA[

select * from Student student where student.rollNumber = :rollNumber

]]-->

</sql-query>

you can define named query in hibernate either by using annotations or XML mapping file, as I said above. @NameQuery is used to define single named query and @NameQueries is used to define multiple named query in hibernate.

@NamedQueries({

@NamedQuery(

name = "findStockByStockCode",

query = "from Stock s where s.stockCode = :stockCode"

)

})

Query query = session.getNamedQuery("findStockByStockCode")

.setString("stockCode", "7277");

############################## Explain Criteria API

Criteria is a simplified API for retrieving entities by composing Criterion objects. This is a very convenient approach for functionality like "search" screens where there is a variable number of conditions to be placed upon the result set.

Example:

List employees = session.createCriteria(Employee.class)

.add(Restrictions.like("name", "a%") )

.add(Restrictions.like("address", "Boston"))

.addOrder(Order.asc("name") )

.list();

############################## How do you switch between relational databases without code changes?

Using Hibernate SQL Dialects, we can switch databases. Hibernate will generate appropriate hql queries based on the dialect defined.

############################## What is Hibernate proxy?

The proxy attribute enables lazy initialization of persistent instances of the class. Hibernate will initially return CGLIB proxies which implement the named interface. The actual persistent object will be loaded when a method of the proxy is invoked.

############################## What is automatic dirty checking?

Automatic dirty checking is a feature that saves us the effort of explicitly asking Hibernate to update the database when we modify the state of an object inside a transaction.

############################## What is query cache in Hibernate?

.Query cache can be used along with second level cache for improved performance. QueryCache actually stores the result of SQL query for future calls. Hibernate support various open source caching solution to implement Query cache e.g. EhCache

############################## What are two types of Collections in hibernate?

Sorted Collection
Ordered Collection

Parameter Sorted Collection Ordered Collection

Sorting Sorted collection uses java's sorting API to sort the collection. Ordered Collections uses order by clause while retrieval of objects Default It is enabled by default It is not enabled by default, you need to enable it explicitly

############################## What is lazy loading in hibernate?

Sometimes you have two entities and there's a relationship between them. For example, you might have an entity called University and another entity called Student

public class University {

private String id;

private String name;

private String address;

private List<Student> students;

// setters and getters

}

Now when you load a University from the database, JPA loads its id, name, and address fields for you. But you have two options for students: to load it together with the rest of the fields (i.e. eagerly) or to load it on-demand (i.e. lazily) when you call the university's getStudents() method.

@OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER)

@JoinColumn(name="countryId")

private List<Student> students;

FetchType.LAZY: It fetches the child entities lazily, that is, at the time of fetching parent entity it just fetches proxy (created by cglib or any other utility) of the child entities and when you access any property of child entity then it is actually fetched by hibernate.

FetchType.EAGER: it fetches the child entities along with parent.

Lazy initialization improves performance by avoiding unnecessary computation and reduce memory requirements.

Eager initialization takes more memory consumption and processing speed is slow.

lazy="true/false in xml

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{width="3.813953412073491in" height="3.1279068241469816in"}{width="2.125in" height="0.3958333333333333in"} Hibernate Tutorial

JDBC vs HIBERNATE

Hibernate Architecture

1. Configuration

2. SessionFactory Object

3. Session Object

4. Transaction Object

5. Query Object

6. Criteria Object

Hibernate Installation

1.Hibernate install using maven

2. Download Hibernate jars & add to project

1. Load Hibernate API into Our Application

2. Load Configurations

3. Open Session

4. Create Transaction Object

5. Close the Connections

1. Choose Database Table

2. POJO class(EmployeeBo.java)

3. O/R Mapping XML(EmployeeBo.hbm.xml)

4. Hibernate Configuration file

Approach 1:

Approach 2:

1. Transient state

2. Persistent state

3. Detached state

List of generators

1.assigned

2.increment

3.identity

4.sequence

5.hilo

6.native

7.foregin

8.uuid

Custom generator

Generators Example

SQL vs HQL

Query Interface

HQL Examples

1. HQL Select Query Example

2. HQL Update/Delete Query Example

3. HQL Insert Query Example

HQL with Aggregate functions

Criteria Interface

Working with Criteria Query Language

Example: Get the details from bank table where balance>3000.

Example: Adding ORDERBY Conditions to Criteria

Example: Adding multiple conditions

Hibernate Projections

Projections Syntax

Example 1: Load Single Column using Projections

Example 2: Load Multiple Columns using Projections

Difference between HQL and CQL

Working with Native SQL Queries

Example

Example 1 : HQL Named Query Example

Example 2 : Native SQL Named Query Example

Relationships in Hibernate

Mapping Directions

1.One-to-One Relationship Mapping Example

2.One-to-Many / Many-to-One Relationship

3.Many to Many Relationship

Cascade Attribute In Hibernate

1.First Level Cache

2.Second Level Cache

Commonly used Annotations in Hibernate

Example: CURD operations using Annotations

Mappings using Annotations

1.one-to-one mapping using Annotations

2.one-to-many Mapping Using Annotations

3.Many-to-many Mapping Using Annotations

Errors & Solutions

org.hibernate.HibernateException: Could not parse configuration: hibernate.cfg.xml

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