Combining Queries

Combining multiple query providers into a single state is straightforward in Riverpod using standard Provider composition.

Standard Pattern: Using Provider

Since queryProvider returns a standard Riverpod provider, you can use Provider or FutureProvider to combine them.

import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:fasq_riverpod/fasq_riverpod.dart';

// 1. Define individual providers
final usersProvider = queryProvider('users'.toQueryKey(), () => api.fetchUsers());
final postsProvider = queryProvider('posts'.toQueryKey(), () => api.fetchPosts());

// 2. Combine them using a simple Provider
final dashboardProvider = Provider<AsyncValue<DashboardData>>((ref) {
  final usersState = ref.watch(usersProvider);
  final postsState = ref.watch(postsProvider);

  // You can return a combined AsyncValue
  if (usersState.hasError) return AsyncValue.error(usersState.error!, usersState.stackTrace!);
  if (postsState.hasError) return AsyncValue.error(postsState.error!, postsState.stackTrace!);

  if (usersState.hasValue && postsState.hasValue) {
    return AsyncValue.data(DashboardData(
      users: usersState.value!,
      posts: postsState.value!,
    ));
  }

  return const AsyncValue.loading();
});

class DashboardData {
  final List<User> users;
  final List<Post> posts;
  DashboardData({required this.users, required this.posts});
}

Dependent Combinations

Sometimes you only want to fetch the second query after the first one has succeeded.

final userProvider = queryProvider('user'.toQueryKey(), () => api.fetchUser());

final userPreferencesProvider = queryProvider(
  'prefs'.toQueryKey(),
  () async {
    final user = ref.read(userProvider).value;
    return await api.fetchPreferences(user!.id);
  },
  // Only enable if user is loaded
  options: QueryOptions(
    enabled: ref.watch(userProvider).hasValue,
  ),
);

Why no combineQueries?

While some libraries provide a specific combineQueries function, Riverpod’s native composition is more powerful and flexible. By using standard providers, you get:

1. Granular Rebuilds: Widgets can watch only the specific part of the combination they need.
2. Type Safety: No need for index-based access or casting.
3. Familiar Patterns: Use the same Riverpod patterns you use for everything else.

Best Practices

• Avoid heavy logic in build: Keep your combinations in providers rather than calculating them inside widget build methods.
• Handle all states: Remember that when combining AsyncValues, you need to decide how to represent the combined loading and error states.
• Use .when on individual providers: If your UI allows it, handle the loading/error states of each query independently for a better user experience (e.g., showing parts of the dashboard while others are still loading).

Next Steps

• queryProvider - Deep dive into standard queries
• Riverpod Patterns - Architecture and best practices