reset graph cache in live query on collection gc (#419)

Co-authored-by: Sam Willis <sam.willis@gmail.com>

Author: alec-watts

.changeset/ready-wasps-search.md

@@ -0,0 +1,5 @@
+---
+"@tanstack/db": patch
+---
+
+Ensure that a new d2 graph is used for live queries that are cleaned up by the gc process. Fixes the "Graph already finalized" error.

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

@@ -625,6 +625,13 @@ export function liveQueryCollectionOptions<
       // Return the unsubscribe function
       return () => {
         unsubscribeCallbacks.forEach((unsubscribe) => unsubscribe())
+
+        // Reset caches so a fresh graph/pipeline is compiled on next start
+        // This avoids reusing a finalized D2 graph across GC restarts
+        graphCache = undefined
+        inputsCache = undefined
+        pipelineCache = undefined
+        collectionWhereClausesCache = undefined
       }
     },
   }

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

@@ -288,4 +288,29 @@ describe(`createLiveQueryCollection`, () => {
     expect(liveQuery.size).toBe(3) // Alice, Charlie, and David are active
     expect(liveQuery.get(4)).toEqual({ id: 4, name: `David`, active: true })
   })
+
+  it(`should not reuse finalized graph after GC cleanup (resubscribe is safe)`, async () => {
+    const liveQuery = createLiveQueryCollection({
+      query: (q) =>
+        q
+          .from({ user: usersCollection })
+          .where(({ user }) => eq(user.active, true)),
+      gcTime: 1,
+    })
+
+    const unsubscribe = liveQuery.subscribeChanges(() => {})
+    await liveQuery.preload()
+    expect(liveQuery.status).toBe(`ready`)
+
+    // Unsubscribe and wait for GC to run and cleanup to complete
+    unsubscribe()
+    const deadline = Date.now() + 500
+    while (liveQuery.status !== `cleaned-up` && Date.now() < deadline) {
+      await new Promise((r) => setTimeout(r, 1))
+    }
+    expect(liveQuery.status).toBe(`cleaned-up`)
+
+    // Resubscribe should not throw (would throw "Graph already finalized" without the fix)
+    expect(() => liveQuery.subscribeChanges(() => {})).not.toThrow()
+  })
 })