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What is Spring Data JPA?

When we work with JPA, we build repository class to integrate with database and puts here some boilerplate codes for crud operations. And also we need to build persistence.xml file for setup configurations like entities.

Spring Data JPA saves us from this boilerplate codes. It provides a high level API to simplify data tier.

Spring Data Repositories

Difference from Jpa repositories;

  • Java interfaces
  • Mapi 1 to 1 with Entity
  • Provides an implementation in runtime

Repository Hierarchy

Only JpaRepository comes from Spring Data JPA, the other repositories are available in Spring Data that means we can use in for example Spring Data MongoDb

Query DSL

Method contracts

  • Query dsl begins with findBy, queryBy, readBy, countBy, getBy
  • Multiple criteria combined with "and", "or"

We use findBy prefix and after that we use entity names with camel case.

The equivalent of this query

    public List<Session> getSessionsThatHaveName(String name) {
        List<Session> ses = entityManager
                .createQuery("select s from Session s where s.sessionName like :name")
                .setParameter("name", "%" + name + "%").getResultList();
        return ses;
    }

is this:

List<Session> findBySessionNameContains(String name);

this method implemented in the background like this

//JPQL
select s from Session s
where s.sessionName like :name

and in sql

select * from session s where s.session_name like = ?

Query Method Return Types

List<Session> findBySessionNameContains(String name);
Session findFistBySessionNameContains(String name);
Long countBySessionNameContains(String name);

the prefix decides the return types.

And or

findByFirstNameAndLastName 
findByFirstNameOrLastName

Equals-is-not

findBySessionLength
findBySessionLengthIs
findBySessionLengthEquals
findBySessionLengthNot

where a.sessionLength = ?1
where a.sesionLength = ?1
where a.sessionLength = ?1
where a.sessionLength != ?1

Like not like

findBySessionNameLike("Java%")                  //We need to pass string in client like Java%
findBySessionNameNotLike("Python%")

Like not like

Similar to like keyworde xcept the % is automatically added

findBySessionNameStartingWith("j") //j%
findBySessionNameEndingWith("j")   //%j
findBySessionNameContaining("j")   //%j

Less than greater than

<, >, <=, >=

findBySessionLengthLessThan(30)
findBySessionLengthLessThanEqual(30)

before after between

findByStartDateBefore(startDate)
findByStartDateBetween(startDate, endDate)

null, is null, not null

findBySpeakerPhotoNull()
findBySpeakerPhotoIsNull()

order by

findByLastNameOrderByFirstNameAsc(name)

Query Annotation

Use for more complex queries.

@Query("query")
List<TicketPrice> get....();

We can use named parameters

@Query("query :maxprice")
List<TicketPrice> get....(@Param("maxPrice));

Native sql queries

@Query("query", nativeQuery=true)
List<TicketPrice> get....();

Modifiable queries, executes queries and return count

@Modifying
@Query("update")
int update....();

JPA Named Queries

Two ways to handle that. First add a method

List<TicketPrice> namedFindTickets(@Param("name") String name)

Second add a query annotation

@Query(name="namedquery name")
sgnature(@Param("name") name)

Paging and Sorting

Define query return page

@Query("select s from Session where s.sessionName like %:name")
Page<Model> queryByPriceRangeAndWoodType(@Param("name") String name
											 Pageable page);

testing in the client

repo.queryByPriceRangeAndWoodType("S", PageRequest.of(1, 5, Sort.by(Sort.Direction.DESC, sessionLength)))

give me one page with 5 result, sort by session length