Dependent Queries

Dependent queries are queries that should only execute after some other data is available.

Usage

Use the enabled option in QueryOptions to delay execution until a condition is met.


// 1. Fetch the User first
final userQuery = QueryBuilder<User>(
  queryKey: 'user'.toQueryKey(),
  /* ... */
);
 
// 2. Fetch Posts *only* when User ID is available
QueryBuilder<List<Post>>(
  // Key depends on user ID
  queryKey: 'posts:${userQuery.state.data?.id}'.toQueryKey(),
  queryFn: () => api.fetchPosts(userQuery.state.data!.id),
 
  // Disable until we have the ID
  options: QueryOptions(
    enabled: userQuery.state.hasData, // <--- The magic switch
  ),
  builder: (context, state) {
    if (state.isIdle) return Text('Waiting for user...');
    /* ... */
  }
)

API

Option	Type	Description
`enabled`	`bool`	Set to `false` to prevent the query from fetching automatically. Defaults to `true`.

Examples

Serial Fetching

Sometimes you need to chain requests A -> B -> C.


// This pattern typically involves nesting QueryBuilders
// or using the result of one query to drive the next.
 
QueryBuilder<User>(
  queryKey: 'user'.toQueryKey(),
  builder: (context, userState) {
    if (!userState.hasData) return Loading();
 
    return QueryBuilder<List<Project>>(
      // Dependent key
      queryKey: 'projects:${userState.data.id}'.toQueryKey(),
      queryFn: () => fetchProjects(userState.data.id),
      // Only run when user is loaded (redundant if nested, but good practice)
      options: QueryOptions(enabled: userState.hasData),
      builder: (context, projectState) {
        // ...
      }
    );
  }
)

Waiting for User Input

Don’t search until the user types something.


QueryBuilder(
  queryKey: 'search:$searchTerm'.toQueryKey(),
  queryFn: () => searchApi(searchTerm),
  options: QueryOptions(
    enabled: searchTerm.isNotEmpty, // Only fetch if text exists
  ),
  /* ... */
)

Lifecycle Dependencies (Cascading Cancellation)

While enabled controls when a query starts, the dependsOn parameter controls when a query stops.

Use dependsOn to link a child query to a parent query. If the parent query is disposed (removed from memory), the child query is automatically cancelled. This prevents orphan requests from consuming resources when their conceptual “owner” is gone.


// Parent Query (e.g., User Profile)
final userKey = 'user:123'.toQueryKey();
final userQuery = client.getQuery(userKey, /* ... */);
 
// Child Query (e.g., User Posts)
client.getQuery(
  'user:123:posts'.toQueryKey(),
  queryFn: () => api.fetchUserPosts(123),
  // 🔗 Link to parent
  dependsOn: userKey,
);

When to use `dependsOn`?

Detail Views: A “User Details” query should depend on the “Users List” query if logically nested.
Drill-downs: Order Items should depend on Order.
Resource ownership: If Query B makes no sense without Query A existing, link them.

Cancellation Behavior

Parent Disposed: When the parent query hits 0 subscribers and its garbage collection timer expires.
Cascade: The QueryClient detects the disposal and immediately runs .cancel() on all registered children.
Effect: Any in-flight network requests for the children are aborted. The children are not removed from cache immediately (they follow their own GC logic), but their fetching is stopped.