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A DataSource in LoopBack 4 is a named configuration for a Connector instance that represents data in an external system. The Connector is used by legacy-juggler-bridge to power LoopBack 4 Repositories for Data operations.

Datasource diagram

Creating a DataSource

It is recommended to use the lb4 datasource command provided by the CLI to generate a DataSource. The CLI will prompt for all necessary connector information and create the following files:

  • ${dataSource.dataSourceName}.datasource.config.json containing the connector configuration
  • ${dataSource.dataSourceName}.datasource.ts containing a class extending juggler.DataSource. This class can be used to override the default DataSource behaviour programaticaly. Note: The connector configuration stored in the .json file is injected into this class using Dependency Injection.

Both the above files are generated in src/datasources/ directory by the CLI. It will also update src/datasources/index.ts to export the new DataSource class.

Example DataSource Class:

import {inject} from '@loopback/core';
import {juggler} from '@loopback/repository';
import config from './db.datasource.config.json';

export class DbDataSource extends juggler.DataSource {
  static dataSourceName = 'db';

    @inject('datasources.config.db', {optional: true})
    dsConfig: object = config,
  ) {