api.md

Collection Guard - API

CollectionGuard provides you an elegant way to subscribe and unsubscribe to a collection.

@Injectable({ providedIn: 'root' })
export class MovieListGuard extends CollectionGuard<MovieState> {
  constructor(service: MovieService) {
    super(service);
  }
}

This Guard is going to subscribe to syncCollection of MovieService when entering the route, and unsubscribe when leaving.

In your RouterModule you would have :

const routes: Route[] = [
  {
    path: 'movies',
    component: MovieListGuard,
    canActivate: [MovieListGuard],
    canDeactivate: [MovieListGuard]
  }
]

---

Subscription Strategy

MovieGuard provides two strategy to deal with subscription.

Loading Strategy

By default the MovieGuard doesn't wait for the Firestore to send the first data. It makes routing fast but the data might not be available when component appears. Then you want to leverage the loading key of Akita :

@Component({
  selector: 'app-movies',
  template: `
    <ng-container *ngIf="loading$ | async; else loaded">
      Loading
    </ng-container>
    <ng-template #loaded>
      <movie-item *ngFor="let movie of movies$ | async"></movie-item>
    </ng-template>
  `
})
export class MovieListComponent implements OnInit {
  public loading$: Observable<boolean>;
  public movies$: Observable<Movie[]>;
  constructor(private query: MovieQuery) {}
  ngOnInit() {
    this.loading$ = this.query.selectLoading();
    this.movies$ = this.query.selectAll();
  }
}

AwaitSync Strategy

You can specify the Guard to wait for Firestore's first push. It might make routing slow, but you're sure that the data is available when component appears.

For that you can use the CollectionGuardConfig decorator:

@Injectable({ providedIn: 'root' })
@CollectionGuardConfig({ awaitSync: true })
export class MovieListGuard extends CollectionGuard<MovieState> {
  constructor(service: MovieService) {
    super(service);
  }
}

---

Custom Sync Function

By default CollectionGuard is going to run syncCollection() of your service. You can override the behavior with the sync getter.

sync(next: ActivatedRouteSnapshot): Observable<string | boolean | any>

The sync getter should return an Observable of string, boolean or any.

• If boolean: canActivate returns the value.
• If string: canActivate returns the UrlTree representation of the string. Useful for redirection.
• Else canActivate always returns true.

IMPORTANT : The return value will only be evaluated if using the Await Strategy.

Example: Sync and Activate a Document

To sync and activate a document when you enter a route, you can do :

@Injectable({ providedIn: 'root' })
export class ActiveMovieGuard extends CollectionGuard<MovieState> {

  constructor(service: MovieService) {
    super(service);
  }

  // Sync and set active
  sync(next: ActivatedRouteSnapshot) {
    return this.service.syncActive({ id: next.params.id });
  }
}

Note: In this case we use the Loading Strategy because we don't need to wait for syncActive.

And in the router :

const routes: Route[] = [
  {
    path: 'movie/:id',
    component: MovieViewComponent,
    canActivate: [ActiveMovieGuard],
    canDeactivate: [ActiveMovieGuard]
  }
]

Example: Sync and Redirect if Empty

As very common feature is to redirect to a specific page if there is no document in the collection. You can do that very easily with CollectionGuard :

@Injectable({ providedIn: 'root' })
@CollectionGuardConfig({ awaitSync: true })
export class MovieListGuard extends CollectionGuard<MovieState> {
  constructor(service: MovieService, private query: MovieQuery) {
    super(service);
  }

  // Sync to collection. If empty redirecto to 'movies/create'
  sync() {
    return this.service.syncCollection().pipe(
      map(_ => this.query.getCount()),
      map(count => count === 0 ? '/movies/create' : true)
    );
  }
}

Note: In this case we use the AwaitSync Strategy because we need canActivate to evaluate the value returned by Firestore.

And in the router :

const routes: Route[] = [
  { path: 'create', component: MovieCreateComponent },
  {
    path: 'list',
    canActivate: [MovieListGuard],
    canDeactivate: [MovieListGuard],
    component: MovieListComponent
  },
]