[Nest.js] 5 - TypeORM / MySql(MariaDB)

Contents
1. TypeORM?
2. TypeORM vs Pure Javascript
3. Why use TypeORM
4. Install modules
5. Create Configuration file
6. Register config file to Root Module

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1. TypeORM?

- ORM(Object Relational Mapping)
   -> Automatically Mapping work between Object and RDB(Relational DataBase)
   -> it has an advantage for changes in object and DB

- It available in the Node.js world

- Written in TypeScript

- We(developers) now focus on thinking and developing for OOP by using TypeORM,
   no longer spending time on creating SQL query

---

2. TypeORM vs Pure Javascript

- TypeORM

// using TypeORM's find method

const boards = Board.find({ title: 'Hello', status: 'PUBLIC'});

- Javascript

db.query('SELECT * FROM boards WHERE title = "Hello" AND status = "PUBLIC" 
         , (err, result) => {
	if(err) {
		throw new Error('Error')
    }
	boards = result.rows;
})

---

3. Why use TypeORM

- Based on Model, it automatically creates DB Table Schema.

- it makes easier to deal with CRUD queries, such as Insert, update, select, and delete.

- it makes mapping between tables( 1:N, N:M)

- TypeORM is easy to unite other modules 

---

4. Install Modules - TypeORM, MySql

$ npm install --save @nestjs/typeorm typeorm mysql

modules installation

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5. Create Configuration file for DB connection

- Create folder 'configs' to save configuration files

- Create file 'typeorm.config.ts' and write below properties

// src/configs/typeorm.config.ts

import { TypeOrmModuleOptions } from '@nestjs/typeorm';

export const TypeORMConfig: TypeOrmModuleOptions = {
  type: 'mysql',
  host: 'localhost',
  port: 3306,
  username: 'root',
  password: '1234',
  database: 'test',
  entities: [__dirname + '/../**/*.entity.{js,ts}'],
  synchronize: true,
};

- entities: [__dirname + '/../**/*.entity.{js,ts}']
-> it registers all entities within the path and naming convention.
-> Alternately, if we need to register specific entity.

import { User } from "./payment/entity/User";
import {Post} from "./blog/entity/Post";

{
  ...
  "entities": [User, Post]
  ...
}

- synchronize : true when in developing and testing
                          : false when in deploying because it sometimes deletes data after colunm removed by accident.

---

6. Register config file to Root Module

- configuration file of DB needed to register in Root Module

// src/app.module.ts

import { Module } from '@nestjs/common';
import { BoardsModule } from './boards/boards.module';
import { TypeOrmModule } from '@nestjs/typeorm';
import { TypeORMConfig } from './configs/typeorm.config';

@Module({
  imports: [
    TypeOrmModule.forRoot(TypeORMConfig),     // register here !
    BoardsModule
  ],
  controllers: [],
  providers: [],
})
export class AppModule {}

- TypeOrmModule.forRoot(configuration)
   -> the configuration applies to all Sub-modules

---

# Connection error solution when testing in local server

- ERROR
Error: ER_NOT_SUPPORTED_AUTH_MODE: Client does not support authentication protocol requested by server; consider upgrading MySQL client

- SOLUTION

ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'password'