fix(query-core): fix combine not updating when queries change with stable reference

.changeset/swift-brooms-teach.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/query-core': patch
+---
+
+fix stable combine reference not updating when queries change dynamically

packages/query-core/src/__tests__/queriesObserver.test.tsx

@@ -394,4 +394,120 @@ describe('queriesObserver', () => {
       { status: 'success', data: 102 },
     ])
   })
+
+  test('should update combined result when queries are added with stable combine reference', () => {
+    const combine = vi.fn((results: Array<QueryObserverResult>) => ({
+      count: results.length,
+      results,
+    }))
+
+    const key1 = queryKey()
+    const key2 = queryKey()
+    const queryFn1 = vi.fn().mockReturnValue(1)
+    const queryFn2 = vi.fn().mockReturnValue(2)
+
+    const observer = new QueriesObserver<{
+      count: number
+      results: Array<QueryObserverResult>
+    }>(queryClient, [{ queryKey: key1, queryFn: queryFn1 }], { combine })
+
+    const [initialRaw, getInitialCombined] = observer.getOptimisticResult(
+      [{ queryKey: key1, queryFn: queryFn1 }],
+      combine,
+    )
+    const initialCombined = getInitialCombined(initialRaw)
+
+    expect(initialCombined.count).toBe(1)
+
+    const newQueries = [
+      { queryKey: key1, queryFn: queryFn1 },
+      { queryKey: key2, queryFn: queryFn2 },
+    ]
+    const [newRaw, getNewCombined] = observer.getOptimisticResult(
+      newQueries,
+      combine,
+    )
+    const newCombined = getNewCombined(newRaw)
+
+    expect(newCombined.count).toBe(2)
+  })
+
+  test('should handle queries being removed with stable combine reference', () => {
+    const combine = vi.fn((results: Array<QueryObserverResult>) => ({
+      count: results.length,
+      results,
+    }))
+
+    const key1 = queryKey()
+    const key2 = queryKey()
+    const queryFn1 = vi.fn().mockReturnValue(1)
+    const queryFn2 = vi.fn().mockReturnValue(2)
+
+    const observer = new QueriesObserver<{
+      count: number
+      results: Array<QueryObserverResult>
+    }>(
+      queryClient,
+      [
+        { queryKey: key1, queryFn: queryFn1 },
+        { queryKey: key2, queryFn: queryFn2 },
+      ],
+      { combine },
+    )
+
+    const [initialRaw, getInitialCombined] = observer.getOptimisticResult(
+      [
+        { queryKey: key1, queryFn: queryFn1 },
+        { queryKey: key2, queryFn: queryFn2 },
+      ],
+      combine,
+    )
+    const initialCombined = getInitialCombined(initialRaw)
+
+    expect(initialCombined.count).toBe(2)
+
+    const newQueries = [{ queryKey: key1, queryFn: queryFn1 }]
+    const [newRaw, getNewCombined] = observer.getOptimisticResult(
+      newQueries,
+      combine,
+    )
+    const newCombined = getNewCombined(newRaw)
+
+    expect(newCombined.count).toBe(1)
+  })
+
+  test('should update combined result when queries are replaced with different ones (same length)', () => {
+    const combine = vi.fn((results: Array<QueryObserverResult>) => ({
+      keys: results.map((r) => r.status),
+      results,
+    }))
+
+    const key1 = queryKey()
+    const key2 = queryKey()
+    const queryFn1 = vi.fn().mockReturnValue(1)
+    const queryFn2 = vi.fn().mockReturnValue(2)
+
+    queryClient.setQueryData(key1, 'cached-1')
+
+    const observer = new QueriesObserver<{
+      keys: Array<string>
+      results: Array<QueryObserverResult>
+    }>(queryClient, [{ queryKey: key1, queryFn: queryFn1 }], { combine })
+
+    const [initialRaw, getInitialCombined] = observer.getOptimisticResult(
+      [{ queryKey: key1, queryFn: queryFn1 }],
+      combine,
+    )
+    const initialCombined = getInitialCombined(initialRaw)
+
+    expect(initialCombined.keys).toEqual(['success'])
+
+    const [newRaw, getNewCombined] = observer.getOptimisticResult(
+      [{ queryKey: key2, queryFn: queryFn2 }],
+      combine,
+    )
+    const newCombined = getNewCombined(newRaw)
+
+    expect(newCombined.keys).toEqual(['pending'])
+  })
 })

packages/query-core/src/queriesObserver.ts

@@ -43,6 +43,7 @@ export class QueriesObserver<
   #combinedResult?: TCombinedResult
   #lastCombine?: CombineFn<TCombinedResult>
   #lastResult?: Array<QueryObserverResult>
+  #lastQueryHashes?: Array<string>
   #observerMatches: Array<QueryObserverMatch> = []
 
   constructor(
@@ -180,11 +181,14 @@ export class QueriesObserver<
     const result = matches.map((match) =>
       match.observer.getOptimisticResult(match.defaultedQueryOptions),
     )
+    const queryHashes = matches.map(
+      (match) => match.defaultedQueryOptions.queryHash,
+    )
 
     return [
       result,
       (r?: Array<QueryObserverResult>) => {
-        return this.#combineResult(r ?? result, combine)
+        return this.#combineResult(r ?? result, combine, queryHashes)
       },
       () => {
         return this.#trackResult(result, matches)
@@ -212,15 +216,28 @@ export class QueriesObserver<
   #combineResult(
     input: Array<QueryObserverResult>,
     combine: CombineFn<TCombinedResult> | undefined,
+    queryHashes?: Array<string>,
   ): TCombinedResult {
     if (combine) {
+      const lastHashes = this.#lastQueryHashes
+      const queryHashesChanged =
+        queryHashes !== undefined &&
+        lastHashes !== undefined &&
+        (lastHashes.length !== queryHashes.length ||
+          queryHashes.some((hash, i) => hash !== lastHashes[i]))
+
       if (
         !this.#combinedResult ||
         this.#result !== this.#lastResult ||
+        queryHashesChanged ||
         combine !== this.#lastCombine
       ) {
         this.#lastCombine = combine
         this.#lastResult = this.#result
+
+        if (queryHashes !== undefined) {
+          this.#lastQueryHashes = queryHashes
+        }
         this.#combinedResult = replaceEqualDeep(
           this.#combinedResult,
           combine(input),

packages/react-query/src/__tests__/useQueries.test.tsx

@@ -1811,4 +1811,56 @@ describe('useQueries', () => {
     expect(renderCount).toBeLessThan(10)
     expect(rendered.getByTestId('query-count').textContent).toBe('queries: 1')
   })
+
+  it('should return correct results when queries count changes with stable combine reference', async () => {
+    const combine = (results: Array<QueryObserverResult>) => results
+
+    const results: Array<{ n: number; length: number }> = []
+
+    function Page() {
+      const [n, setN] = React.useState(0)
+
+      const queries = useQueries(
+        {
+          queries: [...Array(n).keys()].map((i) => ({
+            queryKey: ['dynamic', i],
+            queryFn: () => i,
+          })),
+          combine,
+        },
+        queryClient,
+      )
+
+      results.push({ n, length: queries.length })
+
+      return (
+        <div>
+          <span data-testid="n">{n}</span>
+          <span data-testid="length">{queries.length}</span>
+          <button onClick={() => setN(n + 1)}>Increase</button>
+        </div>
+      )
+    }
+
+    const rendered = render(<Page />)
+
+    expect(rendered.getByTestId('n').textContent).toBe('0')
+    expect(rendered.getByTestId('length').textContent).toBe('0')
+
+    fireEvent.click(rendered.getByRole('button', { name: /increase/i }))
+    await vi.advanceTimersByTimeAsync(0)
+
+    expect(rendered.getByTestId('n').textContent).toBe('1')
+    expect(rendered.getByTestId('length').textContent).toBe('1')
+
+    fireEvent.click(rendered.getByRole('button', { name: /increase/i }))
+    await vi.advanceTimersByTimeAsync(0)
+
+    expect(rendered.getByTestId('n').textContent).toBe('2')
+    expect(rendered.getByTestId('length').textContent).toBe('2')
+
+    results.forEach((result) => {
+      expect(result.length).toBe(result.n)
+    })
+  })
 })