Dealing with Angular 2: Issues with Observables failing to return nested objects from services

I have an angular service that handles the retrieval of user objects. These user objects contain various attributes along with an array of walls. The service returns an observable to the component that calls it. While I am able to successfully create a user object from the JSON data obtained through the HTTP service within the service itself, I encounter an issue where the object returned is null when I subscribe to the service in my component. What could be causing this problem?

// user.ts

import { wall } from './wall';

export class user {
    Id: number;
    EntryType: number;
    UserType: number;
    SubscriptionType: number;
    IsCoach: boolean;
    Username: string;
    Email: string;
    Name: string;
    Password: string;
    Created: string;
    MemberWalls: wall[];
}
//wall.ts
export class wall {
    Title: string;
    ViewItem_Id: number;
}
//authentication.service.ts

authenticate(authRequest: login): Observable<user> {
        let url: string = this.apiUrl + AppSettings.LOGIN_SERVICE;
        let headers = new Headers({
            'Content-Type': AppSettings.CONTENT_TYPE_HEADER,
            'client-secret': AppSettings.CLIENT_SECRET,
            'client-id': AppSettings.CLIENT_ID
        });

        let options = new RequestOptions({ headers: headers });

        return this._http.post(url, authRequest, options) // 
            .map(data => {
                this.authenticated(data);
            })
            .catch(this.handleError);

    }

    private authenticated(res: Response) {
        let body = res.json();
        if (body.StatusCode === 200) {
            localStorage.setItem('auth_token', res.headers.get("access-token"));
            let user1: user = body.Data;
            console.log(user1);
            return body.Data || {};
        }
        else {
            return {};
        }
    }
//login.component.ts

login() {
        this.errorMessage = '';
        this.currentUser = null;

            this._authService.authenticate(this.loginModel)
                .subscribe(user1 => this.currentUser = user1,
                error => this.handleError( error));

    }

Answer №1

One crucial element that you seem to be overlooking is the return statement when mapping the result of the post request.

In modern versions of JavaScript and TypeScript:

  • If an arrow function is defined with parentheses, the return statement must be explicitly included.
  • If an arrow function is defined without parentheses, JavaScript automatically generates a return statement that returns the value of the expression following the arrow sign.

For example:

let f = (data) => this.authenticated(data);;
// Or 
let f = (data) => { return this.authenticated(data); };

Answer №2

Choosing Gunter's response:

The function <i>user1 => this.currentUser = user1</i> is triggered upon data arrival. The code where you left your comment executes well in advance of this.

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