Fix: Live query collections stuck in initialCommit status when source collections are preloaded after creation

.changeset/fast-crabs-change.md

@@ -0,0 +1,5 @@
+---
+"@tanstack/db": patch
+---
+
+Ensure LiveQueryCollections are properly transitioning to ready state when source collections are preloaded after creation of the live query collection

packages/db/src/collection.ts

@@ -392,9 +392,8 @@ export class CollectionImpl<
         this.onFirstReadyCallbacks = []
         callbacks.forEach((callback) => callback())
 
-        // If the collection is empty when it becomes ready, emit an empty change event
         // to notify subscribers (like LiveQueryCollection) that the collection is ready
-        if (this.size === 0 && this.changeListeners.size > 0) {
+        if (this.changeListeners.size > 0) {
           this.emitEmptyReadyEvent()
         }
       }

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

@@ -3,6 +3,7 @@ import { createCollection } from "../../src/collection.js"
 import { createLiveQueryCollection, eq } from "../../src/query/index.js"
 import { Query } from "../../src/query/builder/index.js"
 import { mockSyncCollectionOptions } from "../utls.js"
+import type { ChangeMessage } from "../../src/types.js"
 
 // Sample user type for tests
 type User = {
@@ -189,4 +190,102 @@ describe(`createLiveQueryCollection`, () => {
     })
     expect(liveQuery.isReady()).toBe(false)
   })
+
+  it(`should update after source collection is loaded even when not preloaded before rendering - REPRODUCES BUG`, async () => {
+    // Create a source collection that doesn't start sync immediately
+    let beginCallback: (() => void) | undefined
+    let writeCallback:
+      | ((message: Omit<ChangeMessage<User, string | number>, `key`>) => void)
+      | undefined
+    let markReadyCallback: (() => void) | undefined
+    let commitCallback: (() => void) | undefined
+
+    const sourceCollection = createCollection<User>({
+      id: `delayed-source-collection`,
+      getKey: (user) => user.id,
+      startSync: false, // Don't start sync immediately
+      sync: {
+        sync: ({ begin, commit, write, markReady }) => {
+          beginCallback = begin
+          commitCallback = commit
+          markReadyCallback = markReady
+          writeCallback = write
+          return () => {} // cleanup function
+        },
+      },
+      onInsert: ({ transaction }) => {
+        const newItem = transaction.mutations[0].modified
+        // We need to call begin, write, and commit to properly sync the data
+        beginCallback!()
+        writeCallback!({
+          type: `insert`,
+          value: newItem,
+        })
+        commitCallback!()
+        return Promise.resolve()
+      },
+      onUpdate: () => Promise.resolve(),
+      onDelete: () => Promise.resolve(),
+    })
+
+    // Create a live query collection BEFORE the source collection is preloaded
+    // This simulates the scenario where the live query is created during rendering
+    // but the source collection hasn't been preloaded yet
+    const liveQuery = createLiveQueryCollection((q) =>
+      q
+        .from({ user: sourceCollection })
+        .where(({ user }) => eq(user.active, true))
+    )
+
+    // Initially, the live query should be in idle state (default startSync: false)
+    expect(liveQuery.status).toBe(`idle`)
+    expect(liveQuery.size).toBe(0)
+
+    // Now preload the source collection (simulating what happens after rendering)
+    sourceCollection.preload()
+
+    // Store the promise so we can wait for it later
+    const preloadPromise = liveQuery.preload()
+
+    // Trigger the initial data load first
+    if (beginCallback && writeCallback && commitCallback && markReadyCallback) {
+      beginCallback()
+      // Write initial data
+      writeCallback({
+        type: `insert`,
+        value: { id: 1, name: `Alice`, active: true },
+      })
+      writeCallback({
+        type: `insert`,
+        value: { id: 2, name: `Bob`, active: false },
+      })
+      writeCallback({
+        type: `insert`,
+        value: { id: 3, name: `Charlie`, active: true },
+      })
+      commitCallback()
+      markReadyCallback()
+    }
+
+    // Wait for the preload to complete
+    await preloadPromise
+
+    // The live query should be ready and have the initial data
+    expect(liveQuery.size).toBe(2) // Alice and Charlie are active
+    expect(liveQuery.get(1)).toEqual({ id: 1, name: `Alice`, active: true })
+    expect(liveQuery.get(3)).toEqual({ id: 3, name: `Charlie`, active: true })
+    expect(liveQuery.get(2)).toBeUndefined() // Bob is not active
+    // This test should fail because the live query is stuck in 'initialCommit' status
+    expect(liveQuery.status).toBe(`ready`) // This should be 'ready' but is currently 'initialCommit'
+
+    // Now add some new data to the source collection (this should work as per the original report)
+    sourceCollection.insert({ id: 4, name: `David`, active: true })
+
+    // Wait for the mutation to propagate
+    await new Promise((resolve) => setTimeout(resolve, 10))
+
+    // The live query should update to include the new data
+    expect(liveQuery.size).toBe(3) // Alice, Charlie, and David are active
+    expect(liveQuery.get(4)).toEqual({ id: 4, name: `David`, active: true })
+  })
 })