The type 'Observable<Object>' cannot be assigned to type 'Observable<IUser[]>'

My Api service contains a simple function called getUsers, which is used to fetch all the users on the api.

public getUsers(url: string): Observable<IUser[]>  {
  return this._http.get(url);
} 

The IUser interface I have created has all fields marked as optional for now.

export interface IUser {
  id?: string;
  first_name?: string;
  last_name?: string;
  location?: string;
  followers?: string;
  following?: string;
  checkins?: string;
  image?: string;
}

Here is how I have implemented the service in my component:

export class SocialOverviewContainerComponent implements OnInit {
  public userData = [];
  public showForm = {};
  private _apiService: ApiService;

  constructor(apiService: ApiService) {
    this._apiService = apiService
  }

  public ngOnInit(): void {
    this.getUsersData();
  }

  public getUsersData()  {
    this._apiService.getUsers(ApiSettings.apiBasepath + 'users/')
      .subscribe(users => {
        this.userData = users;
    })
  }
}

I encountered a Type error when compiling:

ERROR in src/app/services/api.service.ts(18,5): error TS2322: Type 'Observable<Object>' is not assignable to type 'Observable<IUser[]>'.
  Type 'Object' is not assignable to type 'IUser[]'.
    The 'Object' type is assignable to very few other types. Did you mean to use the 'any' type instead?
      Property 'includes' is missing in type 'Object'.

I believe my response matches the interface, so I am confused about the error. I have made the field optional for now, so I'm unsure why this issue is occurring.

Although I could resolve it by casting the observable as any, that would defeat the purpose of using Typescript. Any insights on where I might be going wrong would be greatly appreciated.

Thank you in advance

Answer №1

If you find yourself looking to achieve a particular task in RxJS / Angular, there are two ways to go about it depending on the version you are currently working with. Here's a breakdown of the two methods tailored to suit your specific versions:

// For those utilizing RxJS v4 / Angular v2-4 and leveraging the HttpModule...
import 'rxjs/add/operator/map';

public getUsers(url: string): Observable<IUser[]> {
  return this._http.get(url)
    .map((response: Response) => <IUser[]>response.json());
}


// If you're operating on RxJS v5 / Angular 5+ (current iteration), and opting for HttpClientModule over HttpModule which was phased out in Angular v4.
public getUsers(url: string): Observable<IUser[]> {
  return this._http.get<IUser[]>(url);
}

Answer №2

Isn't it always the way? Just when I give up and post a question, I figure out the solution.

The key was to ensure that the .get function in my service matched the type specified in the getUsers function like so:

public getUsers(url: string): Observable<IUser[]>  {
    return this._http.get<IUser[]>(url);
  }

Hopefully, this can assist others who may encounter similar challenges.

Answer №3

For my situation, the solution below proved to be effective:

  fetchUsers(): Observable<User[]> {
      return <Observable<User[]>> this.http.get(this.apiUrl + 'users', super.generateHeader())
      .pipe(catchError(super.handleErrors));
   }

Currently utilizing Angular version 6

Answer №4

For me, a few of the parameter values are in number format. I must change them to string in order to address the problem.

const parameters = new HttpParams()
    .set('param1', myNumProperty1.toString())  
    .set('param2', myNumProperty2.toString());

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