map-operators-get-one-02.ts

export class BookEffects {
  @Effect() getOneBook$ = this.actions$.pipe(
    // Step 1 Type: Observable<InputActionType>
    ofType(INPUT_ACTION_TYPE),
    // Step 2 Type: Observable<Observable<InputActionType>>
    groupBy(action => action.bookId),
    // Step 3 Type: Observable<Observable<BookModel>>,
    map(action$ => action$.pipe(
      exhaustMap(action => this.bookService.getOne(action.bookId),
    )),
    // Step 4 Type: Observable<BookModel>
    mergeAll(),
  );
}