Angular Ngrx State Dependent Actions

C depends on B -> B depends on A.

• First, notice that I am setting the value of the courses property to the result of the switchMap() operator.
• I use the tap() operator to tranparently perform an action (or side effect), in this case, to dispatch() the LoadCoursesForUserAction action. The tap() operator will receive the user that is emitted from the observable that is created using the select() method.
• Finally, using the switchMap() operator, the inner observable (obtaining the user) is complete, returning the observable of the array of Course objects.

public administrator = false;
public group: Observable<Group>;
public users: Observable<Array<User>>;

ngOnInit() {
    this.group = this.activatedRoute.paramMap
    .takeWhile(() => this.alive)
    .tap(params => this.store.dispatch(new LoadGroupAction({ id: params.get('id') })))
    .switchMap(() => this.store.select('userGroup'));

    this.users = this.group
    .tap(group => this.store.dispatch(new LoadUsersInGroupAction({ group: group })))
    .switchMap(() => this.store.select('users'));

    this.administrator = this.group
    .switchMap(group => this.store.select('authUser')
        .switchMap(user => Observable.of(group.security.administrators.indexOf(user.id > -1))
    );
}

ngOnDestroy() {
    this.alive = false;
}

Source: RxJS Antipatterns