Rewrite APPLY over json_each into a join on SQLite

[Aykuttonpc]

SQLite doesn't support APPLY, so projecting a JSON collection currently fails with ApplyNotSupported. SQLite's table-valued functions can reference preceding tables in the FROM clause though, so the APPLY that EF produces for these queries can be expressed as a regular join.

This adds SqliteApplyFlatteningExpressionVisitor, which runs before the existing APPLY validator and rewrites CROSS/OUTER APPLY over a subquery whose only table is json_each into a CROSS/LEFT JOIN over that function, inlining the subquery's projection into the containing SELECT.

Json_collection_in_projection_with_anonymous_projection_of_scalars now translates to:

SELECT "j"."Id", "o"."value" ->> 'Name' AS "Name", "o"."value" ->> 'Number' AS "Number", "o"."key"
FROM "JsonEntitiesBasic" AS "j"
LEFT JOIN json_each("j"."OwnedCollectionRoot", '$') AS "o" ON 1
ORDER BY "j"."Id", "o"."key"

Scope

Only subqueries that do nothing beyond projecting out of json_each are rewritten:

Tables: [JsonEachExpression], Predicate: null, GroupBy: [], Having: null,
Orderings: [], Limit: null, Offset: null, IsDistinct: false

Lifting a predicate or a limit out of the subquery would change what the query means, so anything else still goes through the validator and reports ApplyNotSupported as before. That's why this says "Part of" rather than "Fixes".

Tests

The full SQLite functional suite passes (38367 tests, 0 failures). Nine tests that previously asserted ApplyNotSupported now run against the real query, so their overrides were removed:

• JsonQuerySqliteTest.Json_collection_in_projection_with_anonymous_projection_of_scalars
• ComplexJsonProjectionSqliteTest and OwnedJsonProjectionSqliteTest: SelectMany_associate_collection, SelectMany_nested_collection_on_required_associate, SelectMany_nested_collection_on_optional_associate

The SelectMany ones weren't something I targeted, they started working as a side effect of the rewrite.

One open question

The LEFT JOIN uses a constant true predicate, which renders as ON 1, since there is no real join condition. Let me know if you'd rather see something else there.

Part of #34375

[Copilot]

Pull request overview

This PR improves SQLite query translation by rewriting certain CROSS/OUTER APPLY patterns (which SQLite doesn’t support) into equivalent CROSS/LEFT JOIN forms for trivial json_each subqueries, enabling previously-failing JSON collection projections to translate and execute successfully.

Changes:

• Added SqliteApplyFlatteningExpressionVisitor to flatten eligible APPLY-over-json_each subqueries into joins.
• Hooked the new visitor into SqliteQueryTranslationPostprocessor before the existing APPLY validator.
• Updated/removes SQLite functional test overrides that previously asserted ApplyNotSupported, and added a new SQL assertion for the now-supported translation.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/EFCore.Sqlite.FunctionalTests/Query/JsonQuerySqliteTest.cs	Updates a test to assert the new JOIN-based SQL translation instead of ApplyNotSupported.
test/EFCore.Sqlite.FunctionalTests/Query/Associations/OwnedJson/OwnedJsonProjectionSqliteTest.cs	Removes overrides that existed only to assert APPLY-not-supported for SelectMany JSON cases.
test/EFCore.Sqlite.FunctionalTests/Query/Associations/ComplexJson/ComplexJsonProjectionSqliteTest.cs	Removes overrides that existed only to assert APPLY-not-supported for SelectMany JSON cases.
src/EFCore.Sqlite.Core/Query/Internal/SqliteQueryTranslationPostprocessor.cs	Invokes the new flattening visitor before running the APPLY validator.
src/EFCore.Sqlite.Core/Query/Internal/SqliteApplyFlatteningExpressionVisitor.cs	Implements the APPLY-to-JOIN rewrite and projection inlining for trivial json_each subqueries.