Creating CRUD REST APIs from a model

Starting with a model class and datasource, LoopBack 4 allows you to easily use CRUD REST APIs by convention through @loopback/rest-crud. The package allows the application to use a default CRUD repository and controller class without creating a custom class for either.

The rest-crud example is a simplified version of the Todo example that uses @loopback/rest-crud. To see the rest-crud example, use the following command:

lb4 example rest-crud

Use

To use this functionality, you must already have:

• A LoopBack 4 application (e.g. ExampleApplication)
• At least one model class (e.g. Product)
• At least one datasource (e.g. db)

Model Configuration Options

The ModelCrudRestApiConfig interface provides some options to define and customize the REST API:

Using the example attributes above, a model configuration file would be defined as follows:

import {ModelCrudRestApiConfig} from '@loopback/rest-crud';
import {Product} from '../models';

module.exports = <ModelCrudRestApiConfig>{
  model: Product,
  pattern: 'CrudRest', // make sure to use this pattern
  dataSource: 'db',
  basePath: '/products',
};

CLI Command

LoopBack 4 offers a CLI command to generate the CRUD REST API:

lb4 rest-crud [options]

For example to create CRUD REST API for Product and db:

lb4 rest-crud --datasource db --model Product

You can also create it for multiple models at the same time. For more information on the command, see the Rest Crud generator.

This will generate a model configuration file and add the CrudRestComponent to the application file. For more details, see the following section, under the hood.

Under the Hood

The CLI command installs the @loopback/rest-crud dependency. Then, from @loopback/rest-crud, the CrudRestComponent is added to the application class, as it enables the functionality of creating the CRUD REST APIs from the model and datasource. For example:

// adds the following import
import {CrudRestComponent} from '@loopback/rest-crud';

export class ExampleApplication extends BootMixin(
  RepositoryMixin(RestApplication),
) {
  constructor(options: ApplicationConfig = {}) {
    // other code

    // adds the following line
    this.component(CrudRestComponent);
  }
}

Then it takes the model class and datasource and creates a model configuration file. For example:

import {ModelCrudRestApiConfig} from '@loopback/rest-crud';
import {Product} from '../models';

module.exports = <ModelCrudRestApiConfig>{
  model: Product,
  pattern: 'CrudRest',
  dataSource: 'db',
  basePath: '/products',
};

Under the hood, a default CRUD controller and repository are created using defineCrudControllerClass and defineCrudRepositoryClass, respectively. These two functions can also be used at the application level. For example:

export class ExampleApplication extends BootMixin(
  RepositoryMixin(RestApplication),
) {
  constructor(options: ApplicationConfig = {}) {
    // ...
  }

  async boot(): Promise<void> {
    await super.boot();

    const ProductRepository = defineCrudRepositoryClass(Product);
    const repoBinding = this.repository(ProductRepository);

    inject('datasources.db')(ProductRepository, undefined, 0);

    const ProductController = defineCrudRestController<
      Product,
      typeof Product.prototype.id,
      'id'
    >(Product, {basePath: '/products'});

    inject(repoBinding.key)(ProductController, undefined, 0);
    this.controller(ProductController);
  }
}

Creating it in the application file allows you to create your own repository and only use the default CRUD controller, for example.

Limitations

Currently, the module doesn’t support service-oriented datasources such as REST or SOAP.