fix(db): reject in-place sync row changes without previousValue in development - #1988
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…velopment Core keeps the object a sync source writes as the stored row. A source that changed that object in place and wrote it again had already overwritten the previous value, so live queries saw an update whose old and new values matched and kept a row in a filter it left. In development, the write now throws SyncRowReusedWithoutPreviousValueError unless it names previousValue. The check compares a shallow snapshot of each written object, so rewriting an unchanged object, as the live-query Collection does, stays valid. Production builds skip it. Co-authored-by: Isaac <no-reply@databricks.com>
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Navigate logical layers of code changes, visualize relationships, and explore their blast radius. No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: defaults Review profile: CHILL Plan: Advanced Run ID: 📒 Files selected for processing (3)
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Included review availability: This review used your included allowance. Your plan provides up to 8 included reviews per hour; 4 remain after this review. 📝 WalkthroughWalkthroughDevelopment sync writes now compare shallow snapshots of row objects. An update that changes a previously written object without ChangesReused Sync Row Detection
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~20 minutes Change: Bug fix Sequence Diagram(s)sequenceDiagram
participant SyncWritePath
participant checkReusedRow
participant SyncRowReusedWithoutPreviousValueError
SyncWritePath->>checkReusedRow: Check update containing row value in development
checkReusedRow->>checkReusedRow: Compare row fields with saved snapshot
alt Fields changed and previousValue is absent
checkReusedRow->>SyncRowReusedWithoutPreviousValueError: Create error for row key
SyncRowReusedWithoutPreviousValueError-->>SyncWritePath: Throw error
else
checkReusedRow-->>SyncWritePath: Refresh snapshot
end
Merge Risk: 🔵 Low · up to In development, a failed sync publication followed by a retry of the same mutated row can bypass the new check and leave a live query stale. This is a narrow edge case and does not block merging, but maintainers should account for it. Architecture SummaryArchitecture risk: 🔵 Low · up to The change affects 3 systems. Changed systems: Architecture concerns Review detailsSystems and components
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Full details: Docstring CoverageExplanation Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 4 files. (2 skipped: 2 unsupported.)
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Inline comments:
Review comments at @docs/guides/collection-options-creator.md:
- Around line 188-189: Update both descriptions to clarify that
SyncRowReusedWithoutPreviousValueError is thrown only for changes detected by
the shallow snapshot check; explicitly state that in-place changes to fields
inside existing nested objects are not detected. In
docs/guides/collection-options-creator.md, update the error claim at lines
188–189; in .changeset/reject-reused-sync-rows.md, narrow the release-note claim
at line 5 and include the same limitation.
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The minified public API check lists every exported error, so it needs SyncRowReusedWithoutPreviousValueError. The guide and changeset now say the development check compares shallow copies and misses nested changes. Co-authored-by: Isaac <no-reply@databricks.com>
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Oct 2, 2026
Brings in the reused sync row check (#1988), direct mutation ownership (#1986), insert-not-update for removed keys (#1995), state-stack test gaps (#1996), regenerated API docs (#1989), and the package release (#1971). The released perf-many-filtered-live-queries changeset is dropped, the coverage map keeps both sides' rows, and the mangle cache is regenerated. Co-authored-by: Isaac <no-reply@databricks.com>
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🎯 Changes
A sync source that changes a stored row object in place and writes it again now gets an error in development. Before this change, the write succeeded and live queries could keep the row in a result that it left.
The collection keeps the object that a source passes to
write()as the row's stored value. If the source then changes that object and writes it again, the change already overwrote the previous value. The collection then publishes an update whose old value and new value are the same object. A live query filtered byeq(group, 'a')keeps the row after itsgroupbecame'b'. This affects compiled live queries and the pooled live queries in #1987.Core already supports reused row objects when the write names the previous value (#1835):
How the check works
In development, the sync manager records a shallow copy of each object that a source writes. When the same object comes back as an update without
previousValue, the manager compares it with that copy. A changed object throwsSyncRowReusedWithoutPreviousValueError.previousValueis not checked, and it refreshes the recorded copy.commit, as before.Limits
The copy is shallow, so the check does not detect changes to nested fields.
Docs and evidence
The sync
write()section of the collection options guide now states the rule and shows thepreviousValueform.packages/db/tests/sync-reused-row.test.tscovers five cases:previousValuethrows in development.previousValuemoves the row out of aneqlive query.A mutant without the check fails case 1. A mutant that ignores
previousValuefails cases 2 and 3.The full
@tanstack/dbrun reports 4 type-check errors insubset-error-matrix.test.tsandlocal-storage.test.ts. Cleanmainreports the same 4 errors, so this change does not cause them.✅ Checklist
pnpm test.🚀 Release Impact
This pull request and its description were written by Isaac.
Summary by CodeRabbit
previousValueor write a new object instead. The check is not enabled in production and does not detect nested-field changes.