For current LoopBack 3 users who want to migrate to LoopBack 4, LoopBack 4offers a way to mount your LoopBack 3 application in a LoopBack 4 project. Byadding your application this way, the application’s REST API is included in theOpenAPI spec provided by the LoopBack 4 application. This also means that theLoopBack 3 application’s models can be used with the LoopBack 4 REST APIExplorer.

Mounting the LoopBack 3 Application in a LoopBack 4 Project

Note:

If you are not familiar with LoopBack 4, visitGetting started for an introduction.

Followthis tutorialthat goes through the full steps to mount your application.

To see an example of a mounted application, seelb3-applicationwhich mounts theCoffeeShop example,built from LoopBack 3, in a LoopBack 4 project.

Warning: An important thing to note is that LoopBack 3 applications produce Swagger(OpenAPI version 2), whereas LoopBack 4 produces OpenAPI version 3.Lb3AppBooterComponent converts the Swagger spec from the mounted LoopBack 3application to OpenAPI v3 and adds it to the LoopBack 4 project’s OpenAPI v3spec.

Options

Lb3AppBooterComponentcomes with the option to either mount the full LoopBack 3 application or onlythe rest routes. Default mode is the full application (fullApp).

src/application.ts

this.bootOptions = {
  lb3app: {
    mode: 'restRouter', // only REST routes are mounted
  },
};

To change the path where the main LoopBack 3 application server file is stored,you can modify the path. Default path is ../lb3app/server/server.

src/application.ts

this.bootOptions = {
  lb3app: {
    path: '../coffee-shop/server/server', // server file is found under this path
  },
};

Finally, you can modify the restApiRoot when only mounting the rest router ofyour LoopBack 3 application. Default is restApiRoot is /api.

src/application.ts

this.bootOptions = {
  lb3app: {
    mode: 'restRouter',
    restApiRoot: '/coffees',
  },
};