LoopBack 4 TodoList Application Tutorial - Add TodoList Model
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Building a checklist for your Todo models

A todo item is often grouped into a checklist along with other todo items so that it can be used to measure the progress of a bigger picture.

A data set can often be related to another data set, so that an entity may be able to provide access to another entity based on its relationship with the other entity. To take TodoListApplication one step further and establish relations with the existing Todo model as real-world applications often tend to do, we’ll introduce the model TodoList.

We’ll create the TodoList model to represent a checklist that contains multiple Todo items. Let’s define TodoList model with the following properties:

  • a unique id
  • a title
  • a color to represent the TodoList with

We can use the lb4 model command and answer the prompts to generate the model for us as follows:

$ lb4 model
? Model class name: TodoList
? Please select the model base class Entity
Let's add a property to TodoList
Enter an empty property name when done

? Enter the property name: id
? Property type: number
? Is ID field? Yes
? Required?: No
? Default value [leave blank for none]:

Let's add another property to TodoList
Enter an empty property name when done

? Enter the property name: title
? Property type: string
? Required?: Yes
? Default value [leave blank for none]:

Let's add another property to TodoList
Enter an empty property name when done

? Enter the property name: color
? Property type: string
? Required?: No
? Default value [leave blank for none]:

Let's add another property to TodoList
Enter an empty property name when done

? Enter the property name:
   create src/models/todo-list.model.ts
   update src/models/index.ts

Model TodoList was created in src/models/

Now that we have our new model, we need to define its relation with the Todo model. Add the following import statements and property to the TodoList model:

src/models/todo-list.model.ts

import {hasMany} from '@loopback/repository';
import {Todo} from './todo.model';

@model()
export class TodoList extends Entity {
  // ...properties defined by the CLI...

  @hasMany(() => Todo)
  todos?: Todo[];

  // ...constructor def...
}

The @hasMany() decorator defines this property. As the decorator’s name suggests, @hasMany() informs LoopBack 4 that a todo list can have many todo items.

To complement TodoList’s relationship to Todo, we’ll add in the todoListId property on the Todo model to define the relation on both ends:

src/models/todo.model.ts

@model()
export class Todo extends Entity {
  // ...properties defined by the CLI...

  @property()
  todoListId: number;

  // ...constructor def...
}

Once the models have been completely configured, it’s time to move on to adding a repository for TodoList.

Introduction: TodoList Tutorial

Next step: Add TodoList repository