@loopback/docs

--- lang: en title: 'MySQL Connector Tutorial' keywords: LoopBack 4.0, LoopBack 4, Node.js, TypeScript, OpenAPI, Connector, MySQL, Tutorial sidebar: lb4_sidebar permalink: /doc/en/lb4/Connecting-to-MySQL.html --- # Connecting to MySQL The following tutorial introduces how to set up MySQL as the data source of LoopBack 4 applications with [LoopBack MySQL connector](https://github.com/strongloop/loopback-connector-mysql). ## Prerequisites Before starting this tutorial, make sure you have the following installed: - Node.js version 10 or higher - LoopBack 4 CLI; see [Getting Started with LoopBack 4](../../Getting-started.md) ## Tutorial - MySQL ### 1. Create a new LoopBack 4 app Let's use the [LB4 CLI](../../Command-line-interface.md) `lb4 app` to create a LoopBack 4 application called `MyApp`: ```bash $ lb4 app ? Project name: my-app ? Project description: MySQL connector tutorial ? Project root directory: my-app ? Application class name: MyAppApplication ? Select features to enable in the project (Press <space> to select, <a> to togg le all, <i> to invert selection) ❯◉ Enable eslint: add a linter with pre-configured lint rules ◉ Enable prettier: install prettier to format code conforming to rules ◉ Enable mocha: install mocha to run tests ◉ Enable loopbackBuild: use @loopback/build helpers (e.g. lb-eslint) ◉ Enable vscode: add VSCode config files ◉ Enable docker: include Dockerfile and .dockerignore ◉ Enable repositories: include repository imports and RepositoryMixin (Move up and down to reveal more choices) ``` ### 2. Create models Let's create a simple model `User`. To keep the tutorial short, the prompts of `lb4 model` are skipped: {% include code-caption.html content="user.model.ts" %} ```ts // imports @model() export class User extends Entity { @property({ type: 'number', id: true, generated: true, }) id: number; @property({ type: 'string', }) name?: string; @property({ type: 'boolean', }) hasAccount: boolean; constructor(data?: Partial<User>) { super(data); } } ``` ### 3. Create a data source Next, let's create a DataSource `db` using the MySQL connector by the prompts below: ```bash $ lb4 datasource ? Datasource name: db ? Select the connector for db: ... MongoDB (supported by StrongLoop) ❯ MySQL (supported by StrongLoop) PostgreSQL (supported by StrongLoop) ... ? Connection String url to override other settings (eg: mysql://user:pass@host/db): ? host: localhost ? port: 3306 ? user: loopback ? password: [hidden] // example password: pa55w0rd ? database: demo Datasource Db was created in src/datasources/ ``` Under `src/datasources/db.datasource.ts`, we can find the `DbDataSource` class and the config we just set: ```ts const config = { name: 'db', connector: 'mysql', url: '', host: 'localhost', port: 3306, user: 'loopback', password: 'pa55w0rd', database: 'demo', }; ``` ### 4. Create repositories A [Repository](../../Repository.md) is an artifact that ties the model and the datasource. We will need to create the repository for the `User` class to access the database. The steps of creating `UserRepository` by running `lb4 repository` are skipped here: {% include code-caption.html content="user.repository.ts" %} ```ts // imports export class UserRepository extends DefaultCrudRepository< User, typeof User.prototype.id, UserRelations > { constructor(@inject('datasources.db') dataSource: DbDataSource) { super(User, dataSource); } } ``` ### 5. Database migration LoopBack provides a convenient way to create schemas/tables for our models if we don't have corresponding schemas defined in the relational database. Once we created the above artifacts, run the following commands: **1.** Build the project: ```bash $ npm run build ``` **2.** Migrate database schemas (alter existing tables): ```bash $ npm run migrate ``` This would generate the corresponding MySQL table `User` using the metadata from `User` model via auto-migrate if it does not exist. See [Database Migration](#database-migration) section below for information. If you check the database, you should able to see the table `User`. ``` mysql> describe User; +------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(512) | YES | | NULL | | | hasAccount | tinyint(1) | YES | | NULL | | +------------+--------------+------+-----+---------+----------------+ ``` ### 6. Create endpoints and view data using API Explorer Once we built a [controller](../../Controller.md) with `lb4 controller` to handle requests: ```bash $ lb4 controller ? Controller class name: user Controller User will be created in src/controllers/user.controller.ts ? What kind of controller would you like to generate? REST Controller with CRUD functions ? What is the name of the model to use with this CRUD repository? User ? What is the name of your CRUD repository? UserRepository ? What is the name of ID property? id ? What is the type of your ID? number ? Is the id omitted when creating a new instance? Yes ? What is the base HTTP path name of the CRUD operations? /users ``` Notice that the id is omitted in the request here because it is autogenerated. From the project root, start the app: ```bash $ npm start ``` We can verify what we just created with API Explorer [http://localhost:3000/explorer/](http://localhost:3000/explorer/). ## Database Migration As we showed in the previous steps, [Database migration](../../Database-migrations.md) helps you create relational database schemas based on definitions of your models. Here are some tips: - if you make further changes to models, make sure to run `npm run build` before running the migrate script again - `npm run migrate` alters existing tables for you. If you'd like to drop any existing schemas, you can do `npm run migrate -- --rebuild`. But notice that all the data will be lost. Please check [Database migration](../../Database-migrations.md) for details. Besides the basic model metadata, you can also specify part of the database schema definition via the property definition, which would be mapped to the database. See [Data Mapping Properties](https://loopback.io/doc/en/lb4/MySQL-connector.html#data-mapping-properties). ## Model Discovery While database migration allows you to migrate models to the DB, LoopBack also provides a command [`lb4 discover`](../../Discovering-models.md) to generate models based on schemas from the database. For example, we can try to discover the `user` table we created previously: ```bash $ npm run build $ lb4 discover --schema demo ? Select the connector to discover db ? Select the models which to discover User ? Select a convention to convert db column names(EXAMPLE_COLUMN) to model proper ty names: Camel case (exampleColumn) (Recommended) ? Overwrite src/models/user.model.ts? overwrite force src/models/user.model.ts update src/models/index.ts Models User was created in src/models/ ``` As we can see, the newly generated `User` model would contain database specific details: ```ts // imports @model({ settings: {idInjection: false, mysql: {schema: 'testdb', table: 'User'}}, }) export class User extends Entity { @property({ type: 'number', required: true, // set this to false if the value is auto-generated by the db precision: 10, scale: 0, id: 1, mysql: { columnName: 'id', dataType: 'int', dataLength: null, dataPrecision: 10, dataScale: 0, nullable: 'N', }, }) id: number; @property({ type: 'string', length: 512, mysql: { columnName: 'name', dataType: 'varchar', dataLength: 512, dataPrecision: null, dataScale: null, nullable: 'Y', }, }) name?: string; @property({ type: 'number', precision: 3, scale: 0, mysql: { columnName: 'hasAccount', dataType: 'tinyint', dataLength: null, dataPrecision: 3, dataScale: 0, nullable: 'Y', }, }) hasAccount?: number; // ... } ``` The field `mysql.<property>` maps to the database definition of a table/column. See [Data Mapping Properties](https://loopback.io/doc/en/lb4/MySQL-connector.html#data-mapping-properties) for details.