How can you effectively handle ngxs state changes in your component to respond to loading or error events?

In the PostListComponent, I am iterating over posts retrieved from the server and displaying them using individual PostItemComponents. NGXS is being used for state management in this scenario. When initiating fetchPosts requests, I set the loading state property to true. After a successful request, it is changed back to false. If a request fails, the error object on the state is updated with message and exception properties.

Current implementation:

`
export class PostListComponent implements OnInit {    
  private posts$: Observable<any> = this.store.select(state => state.posts);
  private isLoading: boolean = false;
  private error: object = {};

  constructor(
    public postsFacade: PostsFacadeService,
    public moviesFacade: MoviesFacadeService,
    private store: Store) {    
  }

  ngOnInit() {
    this.posts$.subscribe(
      (state) => this.onLoadingEvent(state)
      );

    this.posts$.subscribe(
      (error) => this.onErrorEvent(error)
    )

  }

  onErrorEvent(error)
  {
    this.error = error.error;
  }

  onLoadingEvent(state)
  {
    this.isLoading = state.loading;  
  }
`

Store structure:

`
@State<PostStateModel>({
    name: 'posts',
    defaults: {
        posts: [],
        loading: false,
        error: {
          message: "",
          error: ""                   
        },
    }
})
`

I believe there might be a more efficient way to subscribe to state changes in the store, possibly utilizing the rxjs mergeMap operator. My current approach works, but I'm open to suggestions on how to better handle store changes within my component.

Answer №1

A couple of key points to consider:

  1. Ensure you have defined some state actions for your state class, such as LoadPosts.
  2. Dispatch the action (perhaps in ngOnInit) before the component loads. This action should call services to fetch data, reducing the dependency on your component.
  3. If the service uses Observables or Promises, make sure to update your state when they return.
  4. You can generate an observable using @Select. This method provides typing for better code safety.

    @Select(PostState) postState$: Observable;

  5. In your component, use the async pipe instead of directly subscribing to postState$ in your code. This simplifies iteration through posts using *ngFor.

  6. By encompassing posts, loading flags, and errors in your state, subscribing to the entire state triggers your function or async pipe whenever any of these elements change. To react only to specific changes, create selector methods with @Selector() within your state class.

Answer №2

One solution to handling heavy errors in your application is setting up an interceptor to catch and manage them as they occur.

ngxs.io/advanced/errors

If you're looking for a lighter approach, consider implementing a response status "slice" called resStatus.

export interface IReqStatus {
  loading?: boolean;
  error?: any;
  success?: boolean;
  action?: string; <-- optionally send along the action this belongs to
}

Here's an example of an action that sends a request to an API endpoint:

@Action(UpdateSomething)
updateSomething(ctx: StateContext<SomeStateModel>, { payload }: any): any {

   // 1. Update the resStatus to show "busy"
  ctx.dispatch(new UpdateResStatus({ loading: true, action: 'updateSomething' }));

  return this.apiService.patch('/something/endpoint', payload).pipe(
    tap((res) => {
      // 2. Update resStatus to show success
      ctx.dispatch(new UpdateResStatus(res));
    }),

    // 3. Update the resStatus with errors
    catchError((err: any) => {
      return ctx.dispatch(new UpdateResStatus(err));
    })
  );
}

An Action can be used to manage the response status:

@Action(UpdateResStatus)
updateResStatus(ctx: StateContext<SomeStateModel>, { payload }: any): Observable<any> {
  let status = {
    loading: false,
    success: payload?.status == 'success',
    error: payload?.status == 'success',
    ...(payload?.action && { action: payload?.action }),
  };
  ctx.setState(patch<SomeStateModel>({ reqStatus: status }));
  return of(payload);
}

If the server responds with a success status, it will update accordingly. However, if the request fails, the reqStatus will be updated using the catchError method.

You can monitor your request statuses using state.reqStatus at any time, and maintain your async pipe's integrity like so:

<button [loading]="$any(reqStatus$ | async).loading" ...>

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