fix(orm): support _count nested inside an include

[ymc9]

Problem

Fixes #2669.

Using _count inside a nested relation's include throws at runtime:

await db.user.findMany({
  include: {
    posts: {
      include: {
        _count: { select: { comments: true } },
      },
    },
  },
});

• SQLite: QueryError: Field "_count" not found in model "Post"
• Postgres/MySQL: missing FROM-clause entry for table "$$t3"

This is valid Prisma syntax (verified against Prisma 6 — it returns posts[].​_count.comments), so it's a Prisma-compatibility gap.

Root cause

The relation-JSON builder resolves a nested payload through two separate branches — one for select and one for include. The select branch already special-cased _count (calling buildCountJson), but the include branch did not:

• SQLite called requireField(schema, 'Post', '_count') → throws.
• Postgres/MySQL emitted a reference to a lateral join ($$..._count.$data) that buildRelationJoins never creates (it only joins real relation fields).

Fix

Apply the same _count handling to the include branch in both dialects, calling buildCountJson with the relation's alias so the count subquery correlates correctly:

• packages/orm/src/client/crud/dialects/sqlite.ts
• packages/orm/src/client/crud/dialects/lateral-join-dialect-base.ts

Why it wasn't caught

The e2e suite covered _count at the top level of select/include and _count nested inside a relation's select — all of which hit the (working) select path. No test nested _count inside an include, the one broken path.

Tests

• Added 'supports _count nested inside an include' to tests/e2e/orm/client-api/find.test.ts, covering _count: { select: ... }, _count: true, and _count with a where filter on the counted relation. Verified it fails against the un-fixed build with the exact issue error and passes with the fix.
• Added tests/regression/test/issue-2669.test.ts (SQLite + Postgres).

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Fixed aggregation count functionality when nested within relation queries.

• Tests

  • Added regression test for nested aggregation counts in relation queries across multiple database providers.

[claude]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: e5c544f9-d016-4a5c-8daf-06debad35611

📥 Commits

Reviewing files that changed from the base of the PR and between 4f462a7 and e6c36ab.

📒 Files selected for processing (4)

• packages/orm/src/client/crud/dialects/lateral-join-dialect-base.ts
• packages/orm/src/client/crud/dialects/sqlite.ts
• tests/e2e/orm/client-api/find.test.ts
• tests/regression/test/issue-2669.test.ts

---

📝 Walkthrough

Walkthrough

Two ORM dialect implementations (SqliteCrudDialect and the lateral-join base) are patched to detect _count as an include field and route it through buildCountJson rather than the generic relation path. A new regression test file for issue-2669 and an extended e2e test validate the fix across SQLite and PostgreSQL.

Changes

_count inside include fix

Layer / File(s)	Summary
Dialect-level _count detection in include processing packages/orm/src/client/crud/dialects/sqlite.ts, packages/orm/src/client/crud/dialects/lateral-join-dialect-base.ts	Both buildRelationJSON (SQLite) and buildRelationObjectArgs (lateral-join base) now check field === '_count' inside payload.include and call buildCountJson to generate the count fragment, instead of falling through to the general nested-relation logic that previously threw a QueryError.
Regression and e2e tests tests/regression/test/issue-2669.test.ts, tests/e2e/orm/client-api/find.test.ts	A new parameterized regression test (SQLite + PostgreSQL) seeds User/Post/Comment records and asserts _count is correctly returned when nested inside include. The e2e test adds three scenarios: _count with select, _count: true, and _count with a filter on the counted relation.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐇 Hop, hop, a count went astray,
Nested in include — it just wouldn't play.
With a branch and a check, _count finds its lane,
buildCountJson called, no more runtime pain!
The rabbit rejoices: the tests all turn green. 🌿

🚥 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 describes the main fix: supporting _count nested inside an include clause, which is the core issue addressed across all modified files.
Linked Issues check	✅ Passed	The PR comprehensively addresses issue #2669 by implementing _count support in include payloads for SQLite and lateral-join dialects, adding regression test coverage, and fixing the runtime error described in the issue.
Out of Scope Changes check	✅ Passed	All code changes are directly scoped to fixing _count handling in include payloads: two dialect implementations, one e2e test, and one regression test—all focused on the reported issue.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/issue-2669-nested-count-include

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