Working with DataSource

• What is DataSource

• Creating a new DataSource

• How to use DataSource

What is DataSource

Your interaction with the database is only possible once you setup a DataSource. TypeORM's DataSource holds your database connection settings and establishes initial database connection or connection pool depending on the RDBMS you use.

In order to establish initial connection / connection pool you must call initialize method of your DataSource instance.

Disconnection (closing all connections in the pool) is made when destroy method is called.

Generally, you call initialize method of the DataSource instance on application bootstrap, and destroy it after you completely finished working with the database. In practice, if you are building a backend for your site and your backend server always stays running - you never destroy a DataSource.

Creating a new DataSource

To create a new DataSource instance you must initialize its constructor by calling new DataSource and assigning to a global variable that you'll use across your application:

import { DataSource } from "typeorm"

const AppDataSource = new DataSource({
    type: "mysql",
    host: "localhost",
    port: 3306,
    username: "test",
    password: "test",
    database: "test",
})

AppDataSource.initialize()
    .then(() => {
        console.log("Data Source has been initialized!")
    })
    .catch((err) => {
        console.error("Error during Data Source initialization", err)
    })

It's a good idea to make AppDataSource globally available by export-ing it, since you'll use this instance across your application.

DataSource accepts DataSourceOptions and those options vary depend on database type you use. For different database types there are different options you can specify.

You can define as many data sources as you need in your application, for example:

import { DataSource } from "typeorm"

const MysqlDataSource = new DataSource({
    type: "mysql",
    host: "localhost",
    port: 3306,
    username: "test",
    password: "test",
    database: "test",
    entities: [
        // ....
    ],
})

const PostgresDataSource = new DataSource({
    type: "postgres",
    host: "localhost",
    port: 5432,
    username: "test",
    password: "test",
    database: "test",
    entities: [
        // ....
    ],
})

How to use DataSource

Once you set your DataSource, you can use it anywhere in your app, for example:

import { AppDataSource } from "./app-data-source"
import { User } from "../entity/User"

export class UserController {
    @Get("/users")
    getAll() {
        return AppDataSource.manager.find(User)
    }
}

Using DataSource instance you can execute database operations with your entities, particularly using .manager and .getRepository() properties. For more information about them see Entity Manager and Repository documentation.