fix(query-core): prevent reducer from being called twice in streamedQuery #9970

HuijungYoon · 2025-12-15T02:00:14Z

fix(query-core): prevent reducer from being called twice in streamedQuery #9787

Fix bug where reducer was called twice for each chunk (once in setQueryData, once in loop)
Store reducer result in variable to avoid duplicate calls
Add test case to verify reducer is only called once per chunk

🎯 Changes

✅ Checklist

I have followed the steps in the Contributing guide.
I have tested this code locally with pnpm run test:pr.

🚀 Release Impact

This change affects published code, and I have generated a changeset.
This change is docs/CI/dev-only (no release).

Summary by CodeRabbit

Bug Fixes
- Fixed an issue where streamed data could be applied twice during a refetch using "replace" mode; stream items are now applied once and the displayed data remains stable during and after refetch.
Tests
- Added a test verifying streamed refetch behavior to ensure stream updates are applied a single time and overall data consistency is preserved.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

…uery TanStack#9787 - Fix bug where reducer was called twice for each chunk (once in setQueryData, once in loop) - Store reducer result in variable to avoid duplicate calls - Add test case to verify reducer is only called once per chunk

changeset-bot · 2025-12-15T02:00:17Z

🦋 Changeset detected

Latest commit: ad98335

The changes in this PR will be included in the next version bump.

Not sure what this means? Click here to learn what changesets are.

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coderabbitai · 2025-12-15T02:00:25Z

Walkthrough

Updated streamedQuery per-chunk handling to precompute the next reduced value, preventing duplicate reducer invocations; added a test that verifies the reducer is not called twice when refetchMode is "replace", and added a changeset entry documenting the fix.

Changes

Cohort / File(s)	Change Summary
Streamed Query Test `packages/query-core/src/__tests__/streamedQuery.test.tsx`	Added test "should not call reducer twice when refetchMode is replace" that asserts reducer invocation counts and observable data before and after a refetch with `replace` mode.
Streamed Query Implementation `packages/query-core/src/streamedQuery.ts`	Changed per-chunk processing to compute `nextResult = reducer(result, chunk)`, pass `nextResult` into `setQueryData`, then assign `result = nextResult` to avoid calling the reducer twice.
Changeset `.changeset/fair-peaches-deny.md`	Added a changeset documenting a bug fix release entry for `@tanstack/query-core`: "Fix streamedQuery reducer being called twice".

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Pay extra attention to:
- streamedQuery.ts per-chunk path where nextResult is computed and passed into setQueryData.
- streamedQuery.test.tsx timing (timer advances) and assertions on reducer call counts and observable data.
- Assumptions about reducer purity or in-place mutation that could be affected by precomputing results.

Possibly related PRs

feat(query-core): add custom reducer support to streamedQuery #9532 — Related changes to streamedQuery reducer usage and per-chunk accumulation logic.

Suggested reviewers

TkDodo
manudeli

Poem

🐇 I hopped through streams of ones and twos,
Collected chunks without repeat blues.
nextResult saved a double call,
Now reducers dance just once—no fall.
🥕✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description check	✅ Passed	The PR description includes the required sections from the template (Changes, Checklist, Release Impact) with all checkboxes completed and specific details about the fix.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Title check	✅ Passed	The title accurately describes the main bug fix: preventing the reducer from being called twice in streamedQuery, which is the primary change in this PR.

✨ Finishing touches

📝 Generate docstrings

🧪 Generate unit tests (beta)

Create PR with unit tests
Post copyable unit tests in a comment

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coderabbitai

Actionable comments posted: 2

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between f15b7fc and bc8d7be.

📒 Files selected for processing (2)

packages/query-core/src/__tests__/streamedQuery.test.tsx (1 hunks)
packages/query-core/src/streamedQuery.ts (1 hunks)

🧰 Additional context used

🧠 Learnings (2)

📓 Common learnings

Learnt from: sukvvon
Repo: TanStack/query PR: 9892
File: packages/solid-query-persist-client/src/__tests__/PersistQueryClientProvider.test.tsx:331-335
Timestamp: 2025-11-22T09:06:05.219Z
Learning: In TanStack/query test files, when a queryFn contains side effects (e.g., setting flags for test verification), prefer async/await syntax for clarity; when there are no side effects, prefer the .then() pattern for conciseness.

📚 Learning: 2025-11-22T09:06:05.219Z

Learnt from: sukvvon
Repo: TanStack/query PR: 9892
File: packages/solid-query-persist-client/src/__tests__/PersistQueryClientProvider.test.tsx:331-335
Timestamp: 2025-11-22T09:06:05.219Z
Learning: In TanStack/query test files, when a queryFn contains side effects (e.g., setting flags for test verification), prefer async/await syntax for clarity; when there are no side effects, prefer the .then() pattern for conciseness.

Applied to files:

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

🧬 Code graph analysis (1)

packages/query-core/src/__tests__/streamedQuery.test.tsx (1)

packages/query-core/src/streamedQuery.ts (1)

streamedQuery (46-97)

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

packages/query-core/src/streamedQuery.ts

Fixed an issue where the reducer was being invoked twice when refetchMode is set to 'replace'. Added a regression test to verify the fix. Fixes TanStack#9787

coderabbitai

Actionable comments posted: 0

🧹 Nitpick comments (1)

packages/query-core/src/__tests__/streamedQuery.test.tsx (1)
501-536: Past review feedback has been addressed correctly.

The test now properly verifies that the reducer is called exactly once per chunk:

Line 525 correctly expects [1, 2, 3] after the initial fetch

Line 532 correctly expects [1, 2, 3, 1, 2, 3] after refetch

The console.log statement has been removed

The test logic is sound and will catch regressions if the double-call bug reappears.

Minor: Extra whitespace in array literal.

Line 525 has trailing whitespace before the closing bracket: [1, 2, 3 ]. Consider removing it for consistency.

Apply this diff:
-    expect(arr).toEqual([1, 2, 3 ])
+    expect(arr).toEqual([1, 2, 3])

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between bc8d7be and d58b43c.

📒 Files selected for processing (2)

packages/query-core/src/__tests__/streamedQuery.test.tsx (1 hunks)
packages/query-core/src/streamedQuery.ts (1 hunks)

🚧 Files skipped from review as they are similar to previous changes (1)

packages/query-core/src/streamedQuery.ts

🧰 Additional context used

🧠 Learnings (1)

📚 Learning: 2025-11-22T09:06:05.219Z

Learnt from: sukvvon
Repo: TanStack/query PR: 9892
File: packages/solid-query-persist-client/src/__tests__/PersistQueryClientProvider.test.tsx:331-335
Timestamp: 2025-11-22T09:06:05.219Z
Learning: In TanStack/query test files, when a queryFn contains side effects (e.g., setting flags for test verification), prefer async/await syntax for clarity; when there are no side effects, prefer the .then() pattern for conciseness.

Applied to files:

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

HuijungYoon · 2025-12-15T13:08:00Z

typo correction
fix correct test case

coderabbitai

Actionable comments posted: 1

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between d58b43c and 7a81504.

⛔ Files ignored due to path filters (1)

pnpm-lock.yaml is excluded by !**/pnpm-lock.yaml

📒 Files selected for processing (2)

.changeset/fair-peaches-deny.md (1 hunks)
packages/query-core/src/__tests__/streamedQuery.test.tsx (1 hunks)

🧰 Additional context used

🧠 Learnings (2)

📚 Learning: 2025-09-02T17:57:33.184Z

Learnt from: TkDodo
Repo: TanStack/query PR: 9612
File: packages/query-async-storage-persister/src/asyncThrottle.ts:0-0
Timestamp: 2025-09-02T17:57:33.184Z
Learning: When importing from tanstack/query-core in other TanStack Query packages like query-async-storage-persister, a workspace dependency "tanstack/query-core": "workspace:*" needs to be added to the package.json.

Applied to files:

.changeset/fair-peaches-deny.md

📚 Learning: 2025-11-22T09:06:05.219Z

Learnt from: sukvvon
Repo: TanStack/query PR: 9892
File: packages/solid-query-persist-client/src/__tests__/PersistQueryClientProvider.test.tsx:331-335
Timestamp: 2025-11-22T09:06:05.219Z
Learning: In TanStack/query test files, when a queryFn contains side effects (e.g., setting flags for test verification), prefer async/await syntax for clarity; when there are no side effects, prefer the .then() pattern for conciseness.

Applied to files:

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

🧬 Code graph analysis (1)

packages/query-core/src/__tests__/streamedQuery.test.tsx (1)

packages/query-core/src/streamedQuery.ts (1)

streamedQuery (46-97)

🔇 Additional comments (1)

packages/query-core/src/__tests__/streamedQuery.test.tsx (1)

501-536: LGTM! Test correctly validates the bug fix.

The test properly verifies that the reducer is invoked only once per chunk (not twice as the bug was causing). The test also correctly validates the refetchMode: 'replace' behavior where:

The reducer is called for each chunk during both initial fetch and refetch

During refetch, cache updates are deferred until the stream completes

The observable data correctly reflects the replaced stream [1, 2, 3] after refetch

.changeset/fair-peaches-deny.md

github-actions bot added the package: query-core label Dec 15, 2025

coderabbitai bot reviewed Dec 15, 2025

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fix(streamed-query): prevent reducer from being called twice

d58b43c

Fixed an issue where the reducer was being invoked twice when refetchMode is set to 'replace'. Added a regression test to verify the fix. Fixes TanStack#9787

coderabbitai bot reviewed Dec 15, 2025

View reviewed changes

HuijungYoon closed this Dec 15, 2025

HuijungYoon reopened this Dec 15, 2025

docs: add changeset and lockfile update

7a81504

coderabbitai bot reviewed Dec 15, 2025

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.changeset/fair-peaches-deny.md Outdated Show resolved Hide resolved

fix(changeset): change version bump to patch

ad98335

HuijungYoon changed the title ~~fix(query-core): prevent reducer from being called twice in streamedQuery #9787~~ fix(query-core): prevent reducer from being called twice in streamedQuery Dec 15, 2025

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fix(query-core): prevent reducer from being called twice in streamedQuery #9970

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