@Chain

export declare let Chain: (Class: any, key?: any, paramIndex?: any) => any;

Each controller has action chain which starts with interceptor filter and end with response filter.

@Chain can be used only as method parameter in action decorators.

@Chain is used to inject data from chained action:

@Filter(100)
export class Cache implements IFilter {


  before(dataFromFilterBefore: string | Buffer): string|Buffer|Promise<string|Buffer> {
    return "1";
  }

  after(dataFromActionChains: string | Buffer): string|Buffer|Promise<string|Buffer> {
    return "7" + dataFromActionChains;
  }

}


@Controller({
   name: "home"
   filters: [Cache]
})
export class HomeController {

  @BeforeEach
  beforeEachAction(@Chain dataFromFilter: string) {
    return "2" + dataFromFilter;
  }


  @Before("action")
  beforeAction(@Chain dataFromBeforeEach: string) {
      return "3" + dataFromBeforeEach;
  }

  @Action("action")
  processAction(@Chain dataFromBefore: string) {
      return "4" + dataFromBefore;
  }

  @After("action")
  afterAction(@Chain dataFromAction: string) {
      return "5" + dataFromAction;
  }

  @AfterEach
  afterEachAction(@Chain dataFromAfterAction: string) {
      return "6" + dataFromAfterAction;
  }

}

If you would execute this action chain you would get result 7654321.

Do you need to define action chains and filters ?

No, It's perfectly fine to define just @Action

@Controller({
   name: "home"
})
export class HomeController {

  @Action("action")
  processAction(@Chain data: string) {
      return "1" + data;
  }

}

In this case @Chain data is empty and you would get result 1undefined.

Do I need to define @Chain in action ?

No if you don't chain actions.

So you probably wondering why do I have chains at all ?

Chains are designed to have shared business logic on different routes or to differentiate some business logic with rendering logic in @Before and in @Action.

You may want to use @BeforeEach to check user session for this controller.

The point is that you can stop chain at any time in logic of your code.

 @Controller({
   name: "home"
})
export class HomeController {

  @Inject(Request) request: Request;

  @Inject(MyService) serviceA: MyService;

  @BeforeEach
  beforeEachAction() {
    if (this.serviceA.shouldStopMe()) {
      this.request.stopChain();
    }
    return "2";
  }

  @Action("action")
  processAction(@Chain dataFromBefore: string) {
      return "4" + dataFromBefore;
  }


}

If shouldStopMe method returns "true" your action chain will be stoped and your result will be "2", beforeAction and processAction methods will not be chained.