What is the best way to arrange a list in Angular2 using AngularFire2's FirebaseListObservable?

Looking to retrieve all users from a Firebase realtime database and organize them based on a score property. I managed to achieve this by using the variable

users: FirebaseListObservable<any[]>;

however, encountered the following errors:

Type 'Observable<any[]>' is not assignable to type 'FirebaseListObservable<any[]>'.
Property '_ref' is missing in type 'Observable<any[]>'.

Switching the variable to
users: Observable<any[]>;
resolves the errors, but limits the use of Angularfire methods like .push() and .update().

The fetching and sorting code (proven to work) is as follows:

this.users = this.af.database.list('/users')
  .map(items => items.sort((a, b) => b.score - a.score));

Seeking advice on the correct approach to avoid errors, or any recommended methods. Thank you!

Answer №1

The FirebaseListObservable class has been implemented to include the lift method, allowing RxJS operators like map to return a FirebaseListObservable instance.

When using TypeScript, RxJS operators are statically typed to return an Observable, requiring a cast to FirebaseListObservable. It's important to note that TypeScript is not essential for using RxJS, as evident from operator creation guidelines that do not mention types.

To confirm that a returned object is a FirebaseListObservable, look for the presence of functions such as push and update as shown in this example:

this.users = this.af.database
  .list('/users')
  .map(items => items.sort((a, b) => b.score - a.score)) as FirebaseListObservable<any[]>;
console.log(this.users.push.toString());
console.log(this.users.update.toString());

It's worth mentioning that this approach may not apply to FirebaseListObservable instances created through queries. A related unanswered question addresses this particular scenario.

Answer №2

Take a look at this helpful example. For more options, check out the Query interface.

this.items = angularFire.database.list('/users', {
  query: {
    orderByChild: 'childPropertyName'
  }
});

export interface Query {
    [key: string]: any;
    orderByKey?: boolean | Observable<boolean>;
    orderByPriority?: boolean | Observable<boolean>;
    orderByChild?: string | Observable<string>;
    orderByValue?: boolean | Observable<boolean>;
    equalTo?: any | Observable<any>;
    startAt?: any | Observable<any>;
    endAt?: any | Observable<any>;
    limitToFirst?: number | Observable<number>;
    limitToLast?: number | Observable<number>;
}

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