Creating-model-runtime.md

lang	en
title	Creating Models at Runtime
keywords	LoopBack 4.0, LoopBack 4, Node.js, TypeScript, OpenAPI, Model
sidebar	lb4_sidebar
permalink	/doc/en/lb4/Creating-model-runtime.html
summary	Create LoopBack Models at runtime

Models can also be created at runtime using the defineModelClass() helper function from the @loopback/repository class. It expects a base model to extend (typically Model or Entity), followed by a ModelDefinition object as shown in the example below.

const bookDef = new ModelDefinition('Book')
  .addProperty('id', {type: 'number', id: true})
  .addProperty('title', {type: 'string'});
const BookModel = defineModelClass<typeof Entity, {id: number; title?: string}>(
  Entity, // Base model
  bookDef, // ModelDefinition
);

You will notice that we are specifying generic parameters for the defineModelClass() function. The first parameter is the base model, the second one is an interface providing the TypeScript description for the properties of the model we are defining. If the interface is not specified, the generated class will have only members inherited from the base model class, which typically means no properties.

In case you need to use an existing Model as the base class, specify the Model as the base class instead of Entity.

// Assuming User is a pre-existing Model class in the app
import {User} from './user.model';
import DynamicModelCtor from '@loopback/repository';
const StudentModel = defineModelClass<
  typeof User,
  // id being provided by the base class User
  {university?: string}
>(User, studentDef);

If you want make this new Model available from other parts of the app, you can call app.model(StudentModel) to create a binding for it.

{% include note.html content=" The app.model() method is available only on application classes with RepositoryMixin applied. " %}