rxjs using combineLatest to filter data stream - stream data is empty when it should not be

Question

I am using combine latest in an angular component to bring together a stream of data with a filter text input:

export class RecordSearchComponent implements OnDestroy {
  @Input() gridData: Observable<TrainingRecord[]> = of([]);

  private filterSubject = new BehaviorSubject<string>('');
  private readonly debounceTimeMs = 300;

  private filterInput$ = this.filterSubject.pipe(
    debounceTime(this.debounceTimeMs),
    distinctUntilChanged(),
  )

  filteredData$ = combineLatest([this.filterInput$, this.gridData]).pipe(
    tap(([filter, data]) => console.log(filter, data)),
    switchMap(([filter, data]) => {
      if (filter === '' || filter === null) {
        return of(data);
      }
      const filterDescriptor = {
        field: 'nameFull',
        operator: 'contains',
        value: filter,
        ignoreCase: true,
      };
      return of(filterBy(data, filterDescriptor));
    })
  );

  ngOnDestroy(): void {
    this.filterSubject.complete();
  }

  onFilter() {
    this.filterSubject.next(this.inputText);
  }
}

The filterSubject is working and I can see the results in the console.

The problem is that the "gridData" value inside combineLatest is always empty. But I can confirm that data is coming in if I subscribe to the gridData on its own in the template. (gridData | async) returns all the records.

Naren Murali · Accepted Answer · 2024-02-08 16:19:41Z

I think if we initialize like this using @Input you might not get the value on initialization, as a safety, you can initialize on ngOnInit.

Also please note: The gridData should have a value when the component is initializing only then it will work!

export class RecordSearchComponent implements OnDestroy {
  @Input() gridData: Observable<TrainingRecord[]> = of([]);

  private filterSubject = new BehaviorSubject<string>('');
  private readonly debounceTimeMs = 300;
  filteredData$!: Observable<TrainingRecord[]> = of([]);

  private filterInput$ = this.filterSubject.pipe(
    debounceTime(this.debounceTimeMs),
    distinctUntilChanged(),
  )

  ngOnInit() {
    this.filteredData$ = combineLatest([this.filterInput$, this.gridData]).pipe(
        tap(([filter, data]) => console.log(filter, data)),
        switchMap(([filter, data]) => {
          if (filter === '' || filter === null) {
            return of(data);
          }
          const filterDescriptor = {
            field: 'nameFull',
            operator: 'contains',
            value: filter,
            ignoreCase: true,
          };
          return of(filterBy(data, filterDescriptor));
        })
      );
  }

  ngOnDestroy(): void {
    this.filterSubject.complete();
  }

  onFilter() {
    this.filterSubject.next(this.inputText);
  }
}

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