Migrating components contributing Models

Please review the content in Migrating models first. Going forward, we assume that you are already familiar with the differences between LoopBack 3 Models and LoopBack 4 Entities & Repositories, and understand how to migrate model-related functionality from a LoopBack 3 application to LoopBack 4.

Import LoopBack 3 models

The first step is to import LoopBack 3 model definitions into your LoopBack 4 component. This will convert LB3 model JSON files into LB4 TypeScript classes, as explained in Import Model definition and Importing models from LoopBack 3 projects.

1. Create a small LB3 app that is using your component.

2. In your LB4 extension project, run lb4 import-lb3-models <path-to-lb3-app> to import model(s) contributed by the component from the LB3 app you created in the previous step. Change the base class of the imported model(s) from Entity to Model if needed.

Migrate behavior-less models

Sometimes, a LoopBack 3 model does not provide any behavior, it is just describing the shape of data (e.g. data fields in a push notification object). Such models can be converted to LoopBack 4 models as follows:

1. Import the LoopBack 3 model to your LoopBack 4 project as explained in Import LoopBack 3 models.

2. Ensure that your component’s main index file exports all models:

   // src/index.ts
   export * from './models';
   

3. Update your documentation to instruct users to import the models directly from the extension, instead of relying on loopback-boot to pick them up.

   import {MyModel} from 'my-extension';
   

4. Optionally, if you want your models to be injectable, add them to the artifacts contributed by the extension.

   import {MyModel} from './models';
   
   export class MyComponent implements Component {
     models: [MyModel];
   }
   

Advanced scenarios

LoopBack 4 does not yet provide recipes for extensions sharing models together with their persistence behavior and their REST APIs. Please join the discussion in loopback-next#5476 to let us know about your use cases and to subscribe for updates.