Automatically subscribe/unsubscribe from TanStack Query based on collection subscriber count (#462)

* Automatically subscribe/unsubscribe from TanStack Query

When a collection backed by a TanStack Query has no active subscribers,
automatically unsubscribe from the query.

* fix types during build

* Add changeset for staleTime bug fix

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

* Clarify startSync JSDoc to explain pause/resume behavior

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

---------

Co-authored-by: Sam Willis <[email protected]>
Co-authored-by: Kyle Mathews <[email protected]>
Co-authored-by: Claude <[email protected]>

Author: 4 people

.changeset/happy-parks-invite.md

@@ -0,0 +1,7 @@
+---
+"@tanstack/query-db-collection": patch
+---
+
+Fix `staleTime` behavior by automatically subscribing/unsubscribing from TanStack Query based on collection subscriber count.
+
+Previously, query collections kept a QueryObserver permanently subscribed, which broke TanStack Query's `staleTime` and window-focus refetch behavior. Now the QueryObserver properly goes inactive when the collection has no subscribers, restoring normal `staleTime`/`gcTime` semantics.

packages/db/src/collection/events.ts

@@ -70,7 +70,7 @@ export class CollectionEventsManager {
     this.listeners.get(event)!.add(callback)
 
     return () => {
-      this.listeners.get(event)!.delete(callback)
+      this.listeners.get(event)?.delete(callback)
     }
   }
 

packages/db/src/types.ts

@@ -334,8 +334,14 @@ export interface BaseCollectionConfig<
    */
   gcTime?: number
   /**
-   * Whether to start syncing immediately when the collection is created.
-   * Defaults to false for lazy loading. Set to true to immediately sync.
+   * Whether to eagerly start syncing on collection creation.
+   * When true, syncing begins immediately. When false, syncing starts when the first subscriber attaches.
+   *
+   * Note: Even with startSync=true, collections will pause syncing when there are no active
+   * subscribers (typically when components querying the collection unmount), resuming when new
+   * subscribers attach. This preserves normal staleTime/gcTime behavior.
+   *
+   * @default false
    */
   startSync?: boolean
   /**

packages/query-db-collection/src/query.ts

@@ -338,6 +338,7 @@ export function queryCollectionOptions(
     throw new QueryClientRequiredError()
   }
 
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (!getKey) {
     throw new GetKeyRequiredError()
   }
@@ -379,8 +380,11 @@ export function queryCollectionOptions(
       any
     >(queryClient, observerOptions)
 
+    let isSubscribed = false
+    let actualUnsubscribeFn: (() => void) | null = null
+
     type UpdateHandler = Parameters<typeof localObserver.subscribe>[0]
-    const handleUpdate: UpdateHandler = (result) => {
+    const handleQueryResult: UpdateHandler = (result) => {
       if (result.isSuccess) {
         // Clear error state
         lastError = undefined
@@ -472,14 +476,45 @@ export function queryCollectionOptions(
       }
     }
 
-    const actualUnsubscribeFn = localObserver.subscribe(handleUpdate)
+    const subscribeToQuery = () => {
+      if (!isSubscribed) {
+        actualUnsubscribeFn = localObserver.subscribe(handleQueryResult)
+        isSubscribed = true
+      }
+    }
+
+    const unsubscribeFromQuery = () => {
+      if (isSubscribed && actualUnsubscribeFn) {
+        actualUnsubscribeFn()
+        actualUnsubscribeFn = null
+        isSubscribed = false
+      }
+    }
+
+    // If startSync=true or there are subscribers to the collection, subscribe to the query straight away
+    if (config.startSync || collection.subscriberCount > 0) {
+      subscribeToQuery()
+    }
+
+    // Set up event listener for subscriber changes
+    const unsubscribeFromCollectionEvents = collection.on(
+      `subscribers:change`,
+      ({ subscriberCount }) => {
+        if (subscriberCount > 0) {
+          subscribeToQuery()
+        } else if (subscriberCount === 0) {
+          unsubscribeFromQuery()
+        }
+      }
+    )
 
     // Ensure we process any existing query data (QueryObserver doesn't invoke its callback automatically with initial
     // state)
-    handleUpdate(localObserver.getCurrentResult())
+    handleQueryResult(localObserver.getCurrentResult())
 
     return async () => {
-      actualUnsubscribeFn()
+      unsubscribeFromCollectionEvents()
+      unsubscribeFromQuery()
       await queryClient.cancelQueries({ queryKey })
       queryClient.removeQueries({ queryKey })
     }

packages/query-db-collection/tests/query.test-d.ts

@@ -1,5 +1,6 @@
 import { describe, expectTypeOf, it } from "vitest"
 import {
+  and,
   createCollection,
   createLiveQueryCollection,
   eq,
@@ -166,7 +167,7 @@ describe(`Query collection type resolution tests`, () => {
       query: (q) =>
         q
           .from({ user: usersCollection })
-          .where(({ user }) => eq(user.active, true) && gt(user.age, 18))
+          .where(({ user }) => and(eq(user.active, true), gt(user.age, 18)))
           .select(({ user }) => ({
             id: user.id,
             name: user.name,