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Service Decorator

@service injects an instance of a given service from a binding matching the service interface.

Syntax: @service(serviceInterface: ServiceInterface, metadata?: InjectionMetadata)

The service interface can be a class. For example:

class MyController {
  constructor(@service(MyService) public myService: MyService) {}
}

If the service is modeled as a TypeScript interface, we need to use a string or symbol to represent the interface as TypeScript interfaces cannot be reflected at runtime.

const MyServiceInterface = 'MyService';
class MyController {
  constructor(@service(MyServiceInterface) public myService: MyService) {}
}

const MyServiceInterface = Symbol('MyService');
class MyController {
  constructor(@service(MyServiceInterface) public myService: MyService) {}
}

If the service interface is not specified, it can be inferred from TypeScript design:type metadata.

class MyController {
  // MyService is inferred from TypeScript design type
  constructor(@service() public myService: MyService) {}
}

Please note the class has to be bound to the context with toClass() or a matching tag named serviceInterface.

const ctx = new Context();
ctx.bind('my-service').toClass(MyService); // The service interface is MyService

or

import {CoreTags, asService} from '@loopback/core';

const myService = new MyService();
ctx
  .bind('my-service')
  .to(myService)
  .tag({[CoreTags.SERVICE_INTERFACE]: MyService});

ctx.bind('my-sub-service').toClass(MySubService).apply(asService(MyService));

The services can also be registered with Application:

const app: Application = ...;
app.service(MyService);
app.service(MySubService, {serviceInterface: MyService});