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This module provides a common set of interfaces for interacting with databases.


This module provides data access facilities to various databases and services as well as the constructs for modeling and accessing those data.


npm install --save @loopback/repository

Basic use

At the moment, we only have implementations of Repository based on LoopBack 3.x loopback-datasource-juggler and connectors. The following steps illustrate how to define repositories and use them with controllers.

Defining a legacy datasource and a model

The repository module provides APIs to define LoopBack 3.x data sources and models. For example,

// src/datasources/db.datasource.ts
import {juggler} from '@loopback/repository';

export const db: juggler.DataSource = new juggler.DataSource({
  name: 'db',
  connector: 'memory',
// src/models/note.model.ts
import {model, Entity, property} from '@loopback/repository';

export class Note extends Entity {
  @property({id: true})
  id: string;
  title: string;
  content: string;

export interface NoteRelations {
  // describe navigational properties here

export type NoteWithRelations = Note & NoteRelations;

NOTE: There is no declarative support for data source and model yet in LoopBack 4. These constructs need to be created programmatically as illustrated above.

Defining a repository

A repository can be created by extending DefaultCrudRepository and using dependency injection to resolve the datasource.

// src/repositories/note.repository.ts
import {DefaultCrudRepository, DataSourceType} from '@loopback/repository';
import {Note, NoteRelations} from '../models';
import {inject} from '@loopback/core';

export class NoteRepository extends DefaultCrudRepository<
> {
  constructor(@inject('datasources.db') protected dataSource: DataSourceType) {
    super(Note, dataSource);

Defining a controller

Controllers serve as handlers for API requests. We declare controllers as classes with optional dependency injection by decorating constructor parameters or properties.

// src/controllers/note.controller.ts
import {repository} from '@loopback/repository';
import {NoteRepository} from '../repositories';
import {Note} from '../models';
import {post, requestBody, get, param} from '@loopback/rest';

export class NoteController {
    // Use constructor dependency injection to set up the repository
    @repository(NoteRepository) public noteRepo: NoteRepository,
  ) {}

  // Create a new note
  create(@requestBody() data: Note) {
    return this.noteRepo.create(data);

  // Find notes by title
  findByTitle(@param.path.string('title') title: string) {
    return this.noteRepo.find({where: {title}});

Run the controller and repository together

Using the Repository Mixin for Application

A Repository Mixin is available for Application that provides convenience methods for binding and instantiating a repository class. Bound instances can be used anywhere in your application using Dependency Injection. The .repository(RepositoryClass) function can be used to bind a repository class to an Application. The mixin will also instantiate any repositories declared by a component in its constructor using the repositories key.

Repositories will be bound to the key repositories.RepositoryClass where RepositoryClass is the name of the Repository class being bound.

We’ll use BootMixin on top of RepositoryMixin so that Repository bindings can be taken care of automatically at boot time before the application starts.

import {BootMixin} from '@loopback/boot';
import {ApplicationConfig} from '@loopback/core';
import {RepositoryMixin} from '@loopback/repository';
import {RestApplication} from '@loopback/rest';
import {db} from './datasources/db.datasource';

export class RepoApplication extends BootMixin(
) {
  constructor(options?: ApplicationConfig) {
    this.projectRoot = __dirname;



Run npm test from the root folder.


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