@loopback/docs/site/tutorials/todo-list/todo-list-tutorial-repository.md

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---
lang: en
title: 'Add TodoList Repository'
keywords: LoopBack 4.0, LoopBack 4, Node.js, TypeScript, OpenAPI, Tutorial
sidebar: lb4_sidebar
permalink: /doc/en/lb4/todo-list-tutorial-repository.html
summary: LoopBack 4 TodoList Application Tutorial - Add TodoList Repository
---

### Repositories with related models

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.

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

Repository TodoListRepository was created in src/repositories/
```

#### Custom Methods

A custom method can be added to the repository class. For example, if we want to
find a `TodoList` with a specific `title` from the repository level, the
following method can be added:

```ts
export class TodoListRepository extends DefaultCrudRepository<
  TodoList,
  typeof TodoList.prototype.id,
  TodoListRelations
> {
  // other code

  // Add the following function
  public findByTitle(title: string) {
    return this.findOne({where: {title}});
  }
}
```

To view the completed file, see the
[`TodoList` example](https://github.com/loopbackio/loopback-next/blob/master/examples/todo-list/src/repositories/todo-list.repository.ts).

### Navigation

Previous step: [Add TodoList model](todo-list-tutorial-model.md)

Last step: [Add Model Relations](todo-list-tutorial-relations.md)