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‎module3-crud-and-data-models/r1-schema-and-data-models/README.md

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## Intoduction to schemas and data modeling
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## Intoduction to database schemas
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### Data modeling
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A database schema is a blueprint or architecture of how our data will look. It doesn’t hold data itself, but instead describes the shape of the data and how it might relate to other tables or models.
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A database model is a type of data model that determines the logical structure of a database. It is the high level design which defines the kind of tables, the `fields` in those tables and the `relations` between different tables.
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The most popular example of a database model is the relational model, which uses a table-based format, which is the one we use in most SQL databases.
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### What are database schemas?
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A database schema is a `blueprint` or `architecture` of how our data will look. It doesn’t hold data itself, but instead describes the shape of the data and how it might relate to other tables or models.
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For example, This is a `Customer` schema in mangodb using mongoose.
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For example, this is a `customer` schema in MongoDB using mongoose.
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```js
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const mongoose = require("mongoose");
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module.exports = mongoose.model("Customer", customer);
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```
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The same `Customer` schema in a MySql database.
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The same `customer` schema in a MySql database.
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```sql
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CREATE TABLE customer (
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```
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We can see that the schema definition for the `Customer` has a `name` which is a type `string` and a `zipcode` that is of type `number`.
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We can see that the schema definition for the `customer` has a `name` which is a type `string` and a `zipcode` that is of type `number`.
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### The Difference between data model and schema
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The database schema is one that contains list of attributes and instructions to tell the database engine how data is organised whereas Data model is a collection of conceptional tools for describing data, data-relationship and consistency constraints.
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The database schema is one that contains list of attributes and instructions to tell the database engine how data is organised whereas data model is a collection of conceptional tools for describing data, data-relationship and consistency constraints.
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## Introduction to CRUD operations
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When we are building APIs, we want our models to provide four basic types of functionality. The model must be able to Create, Read, Update, and Delete resources. Computer scientists often refer to these functions by the acronym `CRUD`. A model should have the ability to perform at most these four functions in order to be complete.
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### CRUD and REST
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### What is REST?
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REST is a set of architectural constraints. API developers can implement REST in a variety of ways. When a client request is made via a RESTful API, it transfers a representation of the state of the resource to the requester or endpoint. This information, or representation, is delivered in one of several formats, JSON is the most generally popular file format to use.
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### CRUD (CREATE, READ, UPDATE, DELETE)
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In a REST environment, CRUD often corresponds to the HTTP methods `POST`, `GET`, `PUT`, and `DELETE`, respectively. These are the fundamental elements of a persistent storage system.
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For example, imagine we are working with a system that is keeping track of meals and their corresponding prices for a restaurant. Let’s look at how we would implement CRUD operations.
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#### Create
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- #### Create
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To create resources in a REST environment, we most commonly use the HTTP POST method. POST creates a new resource of the specified resource type.
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Imagine that we are adding a new food item to the stored list of dishes for this restaurant, and the dish objects are stored in a dishes resource.
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Note: Use `POST` when you want to add a child resource under resources collection.
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Request:
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`POST http://www.myrestaurant.com/api/dishes/`
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We will need to send the `dish` data too.
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`
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Body -
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- #### Read
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```json
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{
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"dish": {
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"name": "Avocado Toast",
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"price": 8
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}
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}
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```
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To read resources in a REST environment, we use the GET method. in practice, reading a resource shouldn't change any information - it should only retrieve it.
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Response: Status Code - 201 (Created)
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This creates a new item with a `name` value of `“Avocado Toast”` and a price value of 8. Upon successful creation, the server should return a header with a link to the newly-created resource.
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#### Read
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To read resources in a REST environment, we use the GET method. Reading a resource should never change any information - it should only retrieve it.
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Note: technically, you can change data in a `GET` request but since we are creating a RESTful API, you shouldn't do that, and, in-general, changing data in a `GET` request would be confusing to the users of your api.
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Request:
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`GET http://www.myrestaurant.com/api/dishes/`
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Response: Status Code - 200 (OK)
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Your response should have a list of `dishes`.
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Body -
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```json
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{
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"dishes": [
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{
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"id": 1,
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"name": "Spring Rolls",
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"price": 6
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},
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{
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"id": 2,
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"name": "Mozzarella Sticks",
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"price": 7
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},
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{
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"id": 1223,
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"name": "Avocado Toast",
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"price": 8
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},
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{
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"id": 1224,
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"name": "Muesli and Yogurt",
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"price": 5
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}
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]
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}
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```
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#### Update
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- #### Update
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PUT is the HTTP method used for the CRUD operation, Update.
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So if the price of Avocado Toast has gone up, we should go into the database and update that information
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So if the price of Avocado Toast has gone up, we should go into the database and update that information using PUT.
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Note: Use `PUT` when you want to modify a singular resource which is already a part of resources collection. `PUT` replaces the resource with the data you send in its entirety.
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Request:
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`PUT http://www.myrestaurant.com/dishes/1223`
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and we send the new data.
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```json
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{
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"dish": {
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"name": "Avocado Toast",
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"price": 10
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}
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}
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```
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Response: Status Code - 200 (OK)
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#### Delete
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- #### Delete
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The CRUD operation Delete corresponds to the HTTP method DELETE. It is used to remove a resource from the system.
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Let’s say that the world avocado shortage has reached a critical point, and we can no longer afford to serve this modern delicacy at all. We should go into the database and delete the item that corresponds to `"Avocado Toast"`, which we know has an `id` of 1223.
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Request:
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`DELETE http://www.myrestaurant.com/dishes/1223`
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Response: Status Code - 204 (NO CONTENT)
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Body - None
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## Resources
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- [See this](https://www.educative.io/blog/crud-operations#what) for more information on how these operations are performed on `SQL` database.
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- [What is REST](https://restfulapi.net/)
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- [database schemas](https://www.educative.io/blog/what-are-database-schemas-examples#types)
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```
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```
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```
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```
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```
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```

‎module3-crud-and-data-models/r1.1-principles-of-setting-up-your-schema/README.md

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## Principles of setting up your schema
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Poorly designed databases can cause many problems, including a waste of resources, difficult maintenance, and faulty performance. That's why having a great database schema design is a crucial part of effective data management.
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Poorly designed databases can cause many problems, including wasting resources, making maintenance difficult, and hindering performance. That's why having a great database schema design is a crucial part of effective data management.
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There are few things to focus on when creating a database schema:
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### Type of database
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Most developers don't see the difference between relation database schema and MongoDB schema, but in reality, it is not the same
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Most developers don't see the difference between relational database schema and MongoDB schema, but in reality, it is not the same
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<img src="https://i.imgur.com/3yobiPB.jpg" alt="meme" width="400"/>
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In a nutshell,
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in `relational databases`, models are usually independent of queries, there is no duplication of data as data will _mostly_ be separated into different tables, and it is rigid, you will have to define types and fields for your schema beforehand.
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in relational databases, models are usually independent of queries, there is no duplication of data as data will _mostly_ be separated into different tables, and it is rigid, you will have to define types and fields for your schema beforehand.
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in the other hand, `MongoDB`, you have more flexibility, there are no rules, documents can have new data or fields at any point of time, no need to define types.
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### Embedding vs. Referencing
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One of the key points to establish a good schema design (especially, if you are using MongoDB) is weither to embed or reference your data, as it can make a big difference in the performance and hardware use.
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One of the key points to establish a good schema design (especially, if you are using MongoDB) is whether to embed or reference your data.
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#### When to `Embed`:
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## Resources
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- [schema design best practices](https://www.youtube.com/watch?v=leNCfU5SYR8)
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- [schema design best practices](https://www.mongodb.com/developer/article/mongodb-schema-design-best-practices/)

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