LoopBack 4 TodoList Application Tutorial - Add TodoList Repository
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One great feature of a related model’s repository is its ability to expose a factory function (a function that returns a newly instantiated object) to return a ‘constrained’ version of the related model’s repository. A factory function is useful because it allows you to create a repository whose operations are limited by the data set that applies to the factory function.

In this section, we’ll build TodoListRepository to have the capability of building a constrained version of TodoRepository.

Create your repository

From inside the project folder, run the lb4 repository command to create a repository for the TodoList model using the db datasource. The db datasource shows up by its class name DbDataSource from the list of available datasources.

lb4 repository
? Please select the datasource DbDatasource
? Select the model(s) you want to generate a repository TodoList
   create src/repositories/todo-list.repository.ts
   update src/repositories/index.ts

Repository TodoList was created in src/repositories/

From there, we’ll need to make two more additions:

  • define the todos property, which will be used to build a constrained TodoRepository
  • inject TodoRepository instance

Once the property type for todos has been defined, use this.createHasManyRepositoryFactoryFor to assign it a repository constraining factory function. Pass in the name of the relationship (todos) and the Todo repository instance to constrain as the arguments for the function.

src/repositories/todo-list.repository.ts

import {Getter, inject} from '@loopback/core';
import {
  DefaultCrudRepository,
  HasManyRepositoryFactory,
  juggler,
  repository,
} from '@loopback/repository';
import {Todo, TodoList} from '../models';
import {TodoRepository} from './todo.repository';

export class TodoListRepository extends DefaultCrudRepository<
  TodoList,
  typeof TodoList.prototype.id
> {
  public readonly todos: HasManyRepositoryFactory<
    Todo,
    typeof TodoList.prototype.id
  >;

  constructor(
    @inject('datasources.db') dataSource: juggler.DataSource,
    @repository.getter(TodoRepository)
    protected todoRepositoryGetter: Getter<TodoRepository>,
  ) {
    super(TodoList, dataSource);
    this.todos = this.createHasManyRepositoryFactoryFor(
      'todos',
      todoRepositoryGetter,
    );
  }
}

We’re now ready to expose TodoList and its related Todo API through the controller.

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