How to get one record from firebase in Angular 2

Question

I'm trying to get one record by uid from my firebase database in Angular 2 app. The problem is that I'm always getting undefinied in profile variable. Could you show me correct way to do this? Thanks! My code:

Profile class

export class Profile{
   constructor(public $key:string, public userId:string, public description:string, public avatarUrl: string){
   }

    static parseFromJson({$key, userId, description, avatarUrl}):Profile{
        return new Profile($key, userId, description, avatarUrl);
    }
}

Profiles service

@Injectable()
export class ProfilesService {
  constructor(private db: AngularFireDatabase) {
  }

  getUserByUserId(userId:string): Observable<Profile>{
    return this.db.list('profiles',{
        query: {
          orderByChild: 'userId',
          equalTo: userId
      }
    }).map(result => Profile.parseFromJson(result[0]));
  }
}

Profile component

export class ProfileComponent {

  profile: Profile;
  uid: string;

  constructor(private profileService: ProfilesService, private af: AngularFire) {
    this.af.auth.subscribe(auth => this.uid = auth.uid);
    this.profileService.getUserByUserId(this.uid).subscribe(
        result => {
          this.profile = result;
        }
     );
   }
}

Answer 1

The result is an array, you might want to take the first value and return as Observable.

.first emits only the first value (or the first value that meets some condition) emitted by the source Observable.

 getUserByUserId(userId:string): Observable<Profile>{
    return this.db.list('profiles',{
        query: {
          orderByChild: 'userId',
          equalTo: userId
      }
    })
    .first()
    .map(result => Profile.parseFromJson(result));