Composition & Mixins

One of the most powerful features of fasq_bloc 0.3.0+ is the ability to compose multiple queries into a single Bloc using the FasqSubscriptionMixin.

The Problem

In complex apps, a single screen often depends on multiple data sources (e.g., a “Dashboard” needs User Profile, Recent Orders, and Notifications). Creating a separate QueryCubit for each one can lead to “Bloc Hell” in your UI:

// The "Bloc Hell" Anti-Pattern
BlocBuilder<UserCubit, ...>(
  builder: (context, userState) {
    return BlocBuilder<OrdersCubit, ...>(
      builder: (context, ordersState) {
         // ... nesting continues ...
      }
    )
  }
)

The Solution: FasqSubscriptionMixin

FasqSubscriptionMixin allows any standard Cubit or Bloc to subscribe to any number of fasq queries. It handles the lifecycle (subscribing, unsubscribing, closing streams) automatically.

Usage

1. Add with FasqSubscriptionMixin to your Cubit.
2. Use subscribeToQuery to listen to updates.

import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:fasq_bloc/fasq_bloc.dart';
 
class DashboardState {
  final User? user;
  final List<Order>? orders;
  final bool isLoading;
 
  // ... constructor & copyWith ...
}
 
class DashboardCubit extends Cubit<DashboardState> with FasqSubscriptionMixin {
  DashboardCubit() : super(DashboardState.initial()) {
    _loadData();
  }
 
  void _loadData() {
    // 1. Get the client (auto-injected via FasqBlocProvider if not passed)
    // Note: You can also use `client` getter from the mixin if initialized manually,
    // or access the global one.
    final client = QueryClient();
 
    // 2. Define Queries
    final userQuery = client.getQuery<User>('user'.toQueryKey(), queryFn: fetchUser);
    final ordersQuery = client.getQuery<List<Order>>('orders'.toQueryKey(), queryFn: fetchOrders);
 
    // 3. Subscribe
    subscribeToQuery<User>(userQuery, (state) {
        emit(state.checkLoading(state).copyWith(user: state.data));
    });
 
    subscribeToQuery<List<Order>>(ordersQuery, (state) {
        emit(state.checkLoading(state).copyWith(orders: state.data));
    });
  }
}

Automatic Cleanup

When your DashboardCubit is closed (e.g., widget unmounted), the mixin automatically cancels all subscriptions to the underlying queries. The queries themselves remain in the cache (shared state), but this Cubit stops listening.

vs MultiQueryBuilder

MultiQueryBuilder is a widget-based approach for the same problem.

• Use FasqSubscriptionMixin when:

  • You have complex business logic combining data.
  • You want to test the logic independent of UI.
  • You need to emit a unified, domain-specific state.

• Use MultiQueryBuilder when:

  • You just need to display data from 2-3 sources without extra logic.
  • You want a quick, widget-only solution.