fix(qc): don't wrap single-statement plans in a transaction

[gordyf]

Fixes prisma/prisma#29748. Supersedes prisma/prisma#29759, following the feedback there that this belongs in Expression::simplify rather than in the query interpreter.

Problem

The query graphs for updateMany and createMany report needs_transaction() == true, so their plans get wrapped in a Transaction expression even though they translate to exactly one SQL statement. A single statement is atomic on its own, so the wrapper only adds BEGIN/COMMIT round-trips — and it makes both operations fail hard on driver adapters without transaction support (e.g. PrismaNeonHttp), while the structurally identical deleteMany executes its single DELETE directly:

Error: Transactions are not supported in HTTP mode
    at PrismaNeonHttpAdapter.startTransaction

Solution

• Expression::simplify now unwraps Transaction(expr) when expr contains at most one statement node (Query/Execute). The new max_statement_count helper computes an upper bound over the expression tree, taking the maximum over mutually exclusive If branches and treating nested Transaction expressions as unbounded.
• translate() wraps the root in Transaction before the simplify pass (previously after), so the new simplification can see the wrapper. Plans with two or more statements keep the transaction exactly as before.

Note on chunking: a single chunkable statement (e.g. a large createMany exceeding the bind-parameter limit) may still be split into multiple queries by the client at runtime, and those chunks now run without a transaction. This matches how chunked deleteMany and read queries — which are never wrapped in a transaction — behave today; a comment in simplify documents this.

Tests

• Added an update-many case to the query translation snapshot tests (there was none).
• Updated create-many and create-many-and-return snapshots: the transaction wrapper around their single statement is gone; multi-statement snapshots (nested writes, m2m, etc.) are unchanged.
• Verified end-to-end by building the query compiler Wasm from this branch, linking it into prisma/prisma (unmodified main), and running a generated client against a driver adapter whose startTransaction rejects: createMany/updateMany now succeed, and explicit $transaction([...]) still fails with the adapter's error as documented.

🤖 Generated with Claude Code

[CLAassistant]

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 0814451b-3a79-465f-9745-dbc56e92414e

📥 Commits

Reviewing files that changed from the base of the PR and between 9b85a55 and c9ffb72.

📒 Files selected for processing (1)

• query-compiler/query-compiler/src/expression.rs

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Summary by CodeRabbit

• Performance

  • Reduced unnecessary transaction overhead by removing transaction wrappers for plans that evaluate to zero or one database statement, while preserving atomic single-statement behavior.

• Bug Fixes

  • Improved transaction handling in the generated query plans, ensuring simplification occurs after transaction wrapping for more consistent behavior across conditional and composite expressions.

• Tests

  • Added/updated fixtures for an updateMany operation on the user model filtered by email and setting their role to administrator.

Walkthrough

The query compiler now calculates an upper bound for database statement nodes across expression trees. Transaction expressions are simplified to Unit when their inner plans contain at most one statement. Root translation now applies transaction wrapping before final simplification. The update-many.json fixture defines a User updateMany request with an email filter, an ADMIN role update, and scalar selection.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly matches the main change: skipping transactions for single-statement plans.
Description check	✅ Passed	The description is directly related to the query-compiler transaction simplification changes.
Linked Issues check	✅ Passed	The PR addresses #29748 by unwrapping single-statement Transaction plans and preserving multi-statement transactions.
Out of Scope Changes check	✅ Passed	The changes shown are scoped to the transaction fix and matching snapshot test updates.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

✨ Simplify code

• Create PR with simplified code

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@query-compiler/query-compiler/src/expression.rs`:
- Around line 262-267: Preserve transactions for chunkable Execute operations by
representing their statement count as potentially multiple or unbounded, or by
propagating explicit chunkability metadata. In
query-compiler/query-compiler/src/expression.rs lines 262-267, update
max_statement_count for Execute; in lines 209-220, remove the transaction only
when the execution-level bound—not merely the AST-node count—proves exactly one
statement.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: a054c1ce-8e58-4ab3-931c-c36eee4342dd

📥 Commits

Reviewing files that changed from the base of the PR and between e922089 and 9b85a55.

⛔ Files ignored due to path filters (3)

• query-compiler/query-compiler/tests/snapshots/queries__queries@create-many-and-return.json.snap is excluded by !**/*.snap
• query-compiler/query-compiler/tests/snapshots/queries__queries@create-many.json.snap is excluded by !**/*.snap
• query-compiler/query-compiler/tests/snapshots/queries__queries@update-many.json.snap is excluded by !**/*.snap

📒 Files selected for processing (3)

• query-compiler/query-compiler/src/expression.rs
• query-compiler/query-compiler/src/translate.rs
• query-compiler/query-compiler/tests/data/update-many.json

[codspeed-hq]

Merging this PR will not alter performance

✅ 11 untouched benchmarks
⏩ 11 skipped benchmarks¹

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_{Comparing gordyf:fix/single-statement-transaction-unwrap (acf5a38) with main (059a7b2)}

Footnotes

1. 11 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[aqrln]

Sorry for the broken CI @gordyf, it looks like some recent changes in the main repo might have broken it. I'll have a look.

resolved