title: Ngrx fetch data only if store is empty
body: <p>Let's assume in my application I have 3 pages: Faculties,Groups,Specialities.</p>
  <p>This is how interface for these entities looks like:</p>
  <pre><code>interface Faculty {
    faculty_id: number;
    faculty_name: string;
    faculty_description: string;
  }
  interface Speciality {
    speciality_id: number;
    speciality_code: string;
    speciality_name: string;
  }
  interface Group {
    group_id: number;
    group_name: string;
    speciality_id: number;
    faculty_id: number;
  }
  </code></pre>
  <p>When I go to page Faculties in <code>ngOnInit</code> I'm checking boolean property in the FacultyState, If faculties  has already been loaded then do not dispatch action else in Effect the service will make  http request.</p>
  <p>The same I've done for Speciality page.</p>
  <h2>Faculty component (Speciality also similar)</h2>
  <pre><code>ngOnInit(): void {
          this.store.pipe(
            select(areFacultiesLoaded),
            tap((hasLoaded) =&gt; {
              if (!hasLoaded) {
                this.store.dispatch(loadAllFaculties())
              }
            })
          ).subscribe();
      
      
         this.faculties$ = this.store.pipe(select(selectAllFaculties))
        }
  </code></pre>
  <h2>Effect</h2>
  <pre><code>@Injectable()
  export class FacultyEffects {
      loadFaculties$ = createEffect(() =&gt; {
          return this.actions$.pipe(
                  ofType(FacultyAction.loadAllFaculties),
                  concatMap(() =&gt; {
                     return this.apiService.getEntity('Faculty').pipe(
                          map(data =&gt; FacultyAction.allFacultiesLoaded({ faculties: data })),
                          catchError(() =&gt; EMPTY)
                          )}
                      ),
          );
      });
  </code></pre>
  <h2>The problem</h2>
  <p>For example I can go to the group page first which also needs faculties and specialties.</p>
  <ol>
  <li>Should I again check If faculties and specialities  have been
  loaded?</li>
  <li>Should I create another action for groups for example - [Groups
  page] fetch all Faculties(Specialities)</li>
  <li>Should I create another effects for those actions?</li>
  </ol>