Update SQL Server VECTOR_SEARCH() support with WithApproximate LINQ operator

[roji]

Updates the EF Core SQL Server provider's vector search support to align with the latest Azure SQL VECTOR_SEARCH() syntax and semantics.

Changes

API changes

• Removed topN parameter from EF.Functions.VectorSearch() (deprecated by SQL Server).
• Added WithApproximate<T>() LINQ operator — opt-in modifier that adds WITH APPROXIMATE to the SQL TOP clause, instructing SQL Server to use the vector index for ANN search. Without it, an exact kNN search is performed.

Design

• WithApproximate() is placed after Take() in the LINQ pipeline, mirroring the T-SQL SELECT TOP(N) WITH APPROXIMATE syntax.
• Internally, WithApproximateExpression wraps the Limit in the SelectExpression. It flows transparently through PushdownIntoSubquery(), preserving WITH APPROXIMATE in inner subqueries (e.g. reranking patterns).
• No implicit ORDER BY is added — users add explicit OrderBy as needed, matching T-SQL behavior.
• Throws InvalidOperationException if WithApproximate() is used without a preceding Take().

Rendering

• WithApproximateExpression is identified and rendered in VisitExtension in SqlServerQuerySqlGenerator, keeping GenerateTop generic.
• The nullability processor treats WithApproximateExpression as a pure pass-through.

Tests (12 tests, all passing against Azure SQL)

• VectorDistance_with_parameter / VectorDistance_with_constant
• VectorSearch_project_entity_and_distance (approximate)
• VectorSearch_exact_knn (no WithApproximate)
• VectorSearch_project_entity_only_with_distance_filter
• VectorSearch_in_subquery
• VectorSearch_with_Where_before_Take / VectorSearch_with_Join_before_Take
• VectorSearch_with_Take_and_Skip (pushdown preserves WITH APPROXIMATE)
• VectorSearch_reranking (approximate inner + exact outer re-rank)
• WithApproximate_without_Take_throws
• Length (VECTORPROPERTY)

NativeAOT compatible

Uses new Func<IQueryable<T>, IQueryable<T>>(WithApproximate).Method pattern instead of MakeGenericMethod.

All APIs remain [Experimental("EF9105")].

Closes #36384

[Copilot]

Pull request overview

Updates EF Core’s SQL Server provider vector search support to match the latest Azure SQL VECTOR_SEARCH() behavior by separating “exact kNN” vs “approximate ANN” via an explicit LINQ opt-in.

Changes:

• Removes the topN parameter from SqlServerQueryableExtensions.VectorSearch() and relies on Take() instead.
• Adds WithApproximate<T>() to render SELECT TOP(N) WITH APPROXIMATE ... for ANN/vector-index usage.
• Wires WithApproximateExpression through SQL generation and nullability processing; expands/updates SQL Server functional tests and string resources.

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/EFCore.SqlServer.FunctionalTests/Query/Translations/VectorTranslationsSqlServerTest.cs	Updates/extends Azure SQL-only tests to cover exact vs approximate vector search SQL.
src/EFCore.SqlServer/Query/Internal/SqlServerSqlNullabilityProcessor.cs	Treats WithApproximateExpression as pass-through during nullability processing.
src/EFCore.SqlServer/Query/Internal/SqlServerQueryableMethodTranslatingExpressionVisitor.cs	Translates WithApproximate() by wrapping SelectExpression.Limit, and validates call shape.
src/EFCore.SqlServer/Query/Internal/SqlServerQuerySqlGenerator.cs	Renders TOP(N) WITH APPROXIMATE by recognizing WithApproximateExpression during SQL generation.
src/EFCore.SqlServer/Query/Internal/SqlExpressions/WithApproximateExpression.cs	New internal SQL expression node used to carry the WITH APPROXIMATE modifier.
src/EFCore.SqlServer/Properties/SqlServerStrings.resx	Adds new user-facing resource strings for WithApproximate() validation errors.
src/EFCore.SqlServer/Properties/SqlServerStrings.Designer.cs	Adds generated accessors for the new resource strings.
src/EFCore.SqlServer/Extensions/SqlServerQueryableExtensions.cs	Updates VectorSearch signature and introduces the WithApproximate() LINQ operator.
src/EFCore.SqlServer/EFCore.SqlServer.baseline.json	Updates API baseline to reflect the signature change and the new experimental API.

Files not reviewed (1)

• src/EFCore.SqlServer/Properties/SqlServerStrings.Designer.cs: Language not supported

Comments suppressed due to low confidence (1)

src/EFCore.SqlServer/Properties/SqlServerStrings.resx:425

• The guidance in this message is misleading: rewriting Skip(...).Take(...).WithApproximate() to Take(...).WithApproximate().Skip(...) is not semantically equivalent (it changes the number of returned rows unless the Take is adjusted to account for the skipped rows). Consider rewording to avoid suggesting an incorrect rewrite, or explicitly describe the correct equivalent rewrite (e.g., taking enough rows to cover the skip) depending on what you intend to support.

  <data name="VectorPropertiesNotSupportedInJson" xml:space="preserve">
    <value>Vector property '{propertyName}' is on '{structuralType}' which is mapped to JSON. Vector properties are not supported within JSON documents.</value>
  </data>

[Copilot]

Pull request overview

Copilot reviewed 15 out of 16 changed files in this pull request and generated 3 comments.

Files not reviewed (1)

• src/EFCore.SqlServer/Properties/SqlServerStrings.Designer.cs: Language not supported

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 1 comment.

Files not reviewed (1)

• src/EFCore.SqlServer/Properties/SqlServerStrings.Designer.cs: Language not supported

[roji]

@AndriySvyryd this should be ready for reviewing - I've added the warning for when EF.Functions.VectorSearch() is used without WithApproximate() on a column with an index, as discussed.

[github-actions]

API review baseline changes for src/EFCore.SqlServer/EFCore.SqlServer.baseline.json

Show diff

The diff below was generated by ApiChief between the base and the PR.

  static class Microsoft.EntityFrameworkCore.Diagnostics.SqlServerEventId
+ static readonly Microsoft.Extensions.Logging.EventId VectorSearchWithoutApproximateWarning

  static class Microsoft.EntityFrameworkCore.SqlServerQueryableExtensions
+ static IQueryable<T> WithApproximate<T>(this IQueryable<T> source);