CODEWITHSUNDEEP
angulartypescriptrxjs
P.S.
P.S.

Reputation: 16384

Is there a way to return single element from array stored as regular Observable?

I use regular observable (not observableArray), which keeps an array of elements, something like this:

public arrayOfItems: IArrayItem[];
public arrayOfItems$: BehaviorSubject<IArrayItem[]> = new BehaviorSubject<IArrayItem[]>(null);

public setArrayOfItems(arrayOfItems: IArrayItem[]): void {
  this.arrayOfItems = arrayOfItems;
  this.arrayOfItems$.next(arrayOfItems);
}

public getArrayOfItems(): Observable<IArrayItem[]> {
  return this.arrayOfItems$.asObservable();
}

And I'd like to implement a getSingleItemFromArray method, which should return a single element from arrayOfItems$ and I'd like to get it asObservable too. Something like this (pseudocode):

public getSingleItemFromArray(): Observable<IArrayItem> {
  return this.arrayOfItems$.find(item => item.condition).asObservable();
}

If it is possible, please, point me to the right direction to implement it.

Upvotes: 3

Views: 2193

Answers (2)

martin
martin

Reputation: 96899

Since arrayOfItems$ is an instance of BehaviorSubject you can use one of the following depending on your use-case:

  1. If you want to just replay the single value you can use:

    return arrayOfItems$.take(1)

    This emits the value cached by the BehaviorSubject and ends the chain with a proper complete notification thanks to take(1).

    Note that you don't have to use asObservable because each operator returns an Observable.

  2. You can actually get the value stored inside BehaviorSubject and return in wrapped with an Observable:

    const val = arrayOfItems$.getValue();
return Observable.of(val);

I'd personally use the first option because it feels more "Rx".

Upvotes: 3

Sachila Ranawaka
Sachila Ranawaka

Reputation: 41427

use Observable.of to converts argument to an observable sequence. 

import { of } from 'rxjs/observable/of';

public getSingleItemFromArray(): Observable<IArrayItem> {
   let item: IArrayItem = this.arrayOfItems$.find(item => item.condition);
   return Observable.of(item )
}

Upvotes: 3

Related Questions