perf(orm): use EXISTS instead of COUNT subquery for to-one relation filters

[evgenovalov]

Summary

• Replaces correlated COUNT(*) > 0 subqueries with EXISTS in buildToOneRelationFilter for relation predicates like { relation: { field: value } }, { relation: { is: {...} } }, and { relation: { isNot: {...} } }
• Sibling fix to perf(orm): use EXISTS instead of COUNT subquery for some/none/every relation filters #2455, which applied the same change to buildToManyRelationFilter (some/none/every)
• is: {...} / default payload → EXISTS (...)
• is: null → NOT EXISTS (...)
• isNot: null → EXISTS (...)
• isNot: {...} → NOT EXISTS (...) OR NOT EXISTS(... WHERE filter)

The old COUNT pattern prevents PostgreSQL from converting the subquery into a semi-join, so the aggregate executes once per parent row. On a production dataset with 2.6M product_site rows and an ~8.5M-row join table, execution time drops from ~2100 ms to ~49 ms (~43×) with the same indexes and the same filter set. EXISTS short-circuits on the first match and the planner picks a Parallel Hash Semi Join driven by the existing covering index.

Fixes #2578.

Test plan

• Added regression test tests/regression/test/issue-2578.test.ts covering:
  • default to-one field predicate ({ user: { name: 'A' } })
  • { user: { is: {...} } }
  • { user: { is: null } }
  • { user: { isNot: null } }
  • { user: { isNot: {...} } } (including rows with no related record)
• Existing issue-2440.test.ts (the some/none/every sibling) still passes
• MySQL's buildExistsExpression override carries over unchanged (derived-table wrapping is handled by the existing helper)

🤖 Generated with Claude Code

Summary by CodeRabbit

Release Notes

• Bug Fixes
  • Fixed to-one relation filtering to correctly handle various filter conditions including null checks, value predicates, and negated filters.

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between ad8d5fb and 2553389.

📒 Files selected for processing (2)

• packages/orm/src/client/crud/dialects/base-dialect.ts
• tests/regression/test/issue-2578.test.ts

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📝 Walkthrough

Walkthrough

This PR refactors the to-one relation filter generation in the base dialect to replace COUNT-based subqueries with EXISTS-based semantics, improving query optimization. A regression test is added to validate the correctness of various to-one relation filter scenarios.

Changes

Cohort / File(s)	Summary
Core Logic Refactoring packages/orm/src/client/crud/dialects/base-dialect.ts	Replaced COUNT-based join subqueries with EXISTS-based semantics in buildToOneRelationFilter. Introduced baseJoin (selecting a constant) and existsSelect helper for optional relation filters. Updated control flow for { is: null }, { is: <value> }, { isNot: null }, { isNot: <value> }, and direct filters to use NOT EXISTS and EXISTS expressions instead of numeric comparisons.
Regression Test Coverage tests/regression/test/issue-2578.test.ts	Added new test suite for issue #2578 verifying to-one relation filter correctness across five scenarios: direct field predicates, is and isNot filters with values/null, and combinations testing expected result sets.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related issues

• Performance: where { relation: { some } } generates slow correlated COUNT subquery instead of EXISTS #2440 — This PR fixes the equivalent performance issue for to-one relations using the same EXISTS-based approach that was applied to to-many relations in PR #2455.

Possibly related PRs

• perf(orm): use EXISTS instead of COUNT subquery for some/none/every relation filters #2455 — Both PRs modify packages/orm/src/client/crud/dialects/base-dialect.ts to replace COUNT-based subqueries with EXISTS-based helpers and buildExistsExpression, establishing a consistent query generation pattern across relation filter types.

Poem

🐰 ✨ A hop and a skip through databases vast,
COUNT joins are slow, but EXISTS is fast!
No more correlated SubPlans take flight,
Just semi-joins now—blazing through night! 🚀

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: replacing COUNT subqueries with EXISTS for to-one relation filters, which is the core optimization described in the changeset.
Linked Issues check	✅ Passed	The code changes successfully implement the proposed fix from issue #2578: refactoring buildToOneRelationFilter to use EXISTS/NOT EXISTS instead of COUNT comparisons, with comprehensive regression tests covering all filter patterns.
Out of Scope Changes check	✅ Passed	All changes are scoped to the stated objectives: modifications to buildToOneRelationFilter logic and a new regression test file for issue #2578, with no extraneous alterations.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[ymc9]

LGTM. Thanks for making this great fix @evgenovalov !