Fix complex property projection for entity splitting mappings

[Copilot]

Queries over split entities (SplitToTable) with a non-JSON ComplexProperty could fail during relational projection with Sequence contains more than one element.
The failure came from assuming a single complex-type mapping table in the split-entity projection path.

• Root cause in relational projection

  • CreateSelect (entity-splitting branch) selected the complex property table via:
    • complexProperty.ComplexType.GetQueryMappings().Single().Table
  • Under split mappings, that assumption is invalid and can produce ambiguous/multiple mappings.

• Query pipeline change

  • Replaced single-mapping table selection with table resolution based on actual mapped columns in projected mappings.
  • Added FindTable/TryFindTable helpers to resolve the table by:
    1. JSON container column (for JSON complex types),
    2. concrete complex properties,
    3. nested complex properties recursively,
    4. fallback to previous mapping-based behavior when no mapped column is found.

• Regression coverage

  • Added Complex_property_on_split_entity in AdHocComplexTypeQueryRelationalTestBase.
  • Scenario models Hook + HookMetadata split table with Hook.Number as complex type, and asserts materialization of both root and complex members.

// Before (assumed one mapping table)
var table = complexProperty.ComplexType.GetQueryMappings().Single().Table;

// After (resolve from projected mappings/columns)
var table = FindTable(complexProperty, mappings);

[Copilot]

Pull request overview

Fixes a relational query translation failure when projecting complex properties on split entities (SplitToTable) by resolving the complex property’s table based on actual mapped columns rather than assuming a single complex-type table mapping.

Changes:

• Updated the entity-splitting projection path in CreateSelect to determine the complex-property table via new FindTable/TryFindTable helpers using mapped columns (with JSON container support and nested complex-property recursion).
• Added a regression test covering a split entity with a non-JSON complex property to ensure materialization works end-to-end.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
test/EFCore.Relational.Specification.Tests/Query/AdHocComplexTypeQueryRelationalTestBase.cs	Adds regression test Complex_property_on_split_entity for split-entity materialization with a non-JSON complex property.
src/EFCore.Relational/Query/RelationalQueryableMethodTranslatingExpressionVisitor.CreateSelect.cs	Fixes table resolution for complex properties under entity splitting by choosing a table based on mapped columns instead of Single() query mapping.