Update SQL Server VECTOR_SEARCH() support with WithApproximate LINQ operator

src/EFCore.SqlServer/Design/Internal/SqlServerCSharpRuntimeAnnotationCodeGenerator.cs

@@ -105,8 +105,6 @@ public override void Generate(IIndex index, CSharpRuntimeAnnotationCodeGenerator
             annotations.Remove(SqlServerAnnotationNames.FillFactor);
             annotations.Remove(SqlServerAnnotationNames.SortInTempDb);
             annotations.Remove(SqlServerAnnotationNames.DataCompression);
-            annotations.Remove(SqlServerAnnotationNames.VectorIndexMetric);
-            annotations.Remove(SqlServerAnnotationNames.VectorIndexType);
             annotations.Remove(SqlServerAnnotationNames.FullTextIndex);
             annotations.Remove(SqlServerAnnotationNames.FullTextCatalog);
             annotations.Remove(SqlServerAnnotationNames.FullTextChangeTracking);
@@ -128,8 +126,6 @@ public override void Generate(ITableIndex index, CSharpRuntimeAnnotationCodeGene
             annotations.Remove(SqlServerAnnotationNames.FillFactor);
             annotations.Remove(SqlServerAnnotationNames.SortInTempDb);
             annotations.Remove(SqlServerAnnotationNames.DataCompression);
-            annotations.Remove(SqlServerAnnotationNames.VectorIndexMetric);
-            annotations.Remove(SqlServerAnnotationNames.VectorIndexType);
             annotations.Remove(SqlServerAnnotationNames.FullTextIndex);
             annotations.Remove(SqlServerAnnotationNames.FullTextCatalog);
             annotations.Remove(SqlServerAnnotationNames.FullTextChangeTracking);

src/EFCore.SqlServer/Diagnostics/Internal/SqlServerLoggingDefinitions.cs

@@ -202,4 +202,12 @@ public class SqlServerLoggingDefinitions : RelationalLoggingDefinitions
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
     public EventDefinitionBase? LogMissingViewDefinitionRights;
+
+    /// <summary>
+    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+    ///     any release. You should only use it directly in your code with extreme caution and knowing that
+    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+    /// </summary>
+    public EventDefinitionBase? LogVectorSearchWithoutApproximate;
 }

src/EFCore.SqlServer/Diagnostics/SqlServerEventId.cs

@@ -33,6 +33,7 @@ private enum Id
         DecimalTypeKeyWarning,
         SavepointsDisabledBecauseOfMARS,
         JsonTypeExperimental, // No longer used
+        VectorSearchWithoutApproximateWarning,
 
         // Scaffolding events
         ColumnFound = CoreEventId.ProviderDesignBaseId,
@@ -145,6 +146,20 @@ private static EventId MakeTransactionId(Id id)
     /// </remarks>
     public static readonly EventId SavepointsDisabledBecauseOfMARS = MakeTransactionId(Id.SavepointsDisabledBecauseOfMARS);
 
+    private static readonly string QueryPrefix = DbLoggerCategory.Query.Name + ".";
+
+    private static EventId MakeQueryId(Id id)
+        => new((int)id, QueryPrefix + id);
+
+    /// <summary>
+    ///     A <c>VectorSearch</c> query was translated without <c>WithApproximate()</c>.
+    ///     Without <c>WithApproximate()</c>, the query performs an exact brute-force search instead of using any vector index.
+    /// </summary>
+    /// <remarks>
+    ///     This event is in the <see cref="DbLoggerCategory.Query" /> category.
+    /// </remarks>
+    public static readonly EventId VectorSearchWithoutApproximateWarning = MakeQueryId(Id.VectorSearchWithoutApproximateWarning);
+
     private static readonly string ScaffoldingPrefix = DbLoggerCategory.Scaffolding.Name + ".";
 
     private static EventId MakeScaffoldingId(Id id)

src/EFCore.SqlServer/EFCore.SqlServer.baseline.json

@@ -1300,6 +1300,9 @@
         },
         {
           "Member": "static readonly Microsoft.Extensions.Logging.EventId UniqueConstraintFound"
+        },
+        {
+          "Member": "static readonly Microsoft.Extensions.Logging.EventId VectorSearchWithoutApproximateWarning"
         }
       ]
     },
@@ -2662,6 +2665,10 @@
         {
           "Member": "static System.Linq.IQueryable<Microsoft.EntityFrameworkCore.VectorSearchResult<T>> VectorSearch<T, TVector>(this Microsoft.EntityFrameworkCore.DbSet<T> source, System.Linq.Expressions.Expression<System.Func<T, TVector>> vectorPropertySelector, TVector similarTo, string metric);",
           "Stage": "Experimental"
+        },
+        {
+          "Member": "static System.Linq.IQueryable<T> WithApproximate<T>(this System.Linq.IQueryable<T> source);",
+          "Stage": "Experimental"
         }
       ]
     },

src/EFCore.SqlServer/Extensions/Internal/SqlServerLoggerExtensions.cs

@@ -637,4 +637,32 @@ public static void MissingViewDefinitionRightsWarning(
 
         // No DiagnosticsSource events because these are purely design-time messages
     }
+
+    /// <summary>
+    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+    ///     any release. You should only use it directly in your code with extreme caution and knowing that
+    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+    /// </summary>
+    public static void VectorSearchWithoutApproximateWarning(
+        this IDiagnosticsLogger<DbLoggerCategory.Query> diagnostics,
+        string propertyName,
+        string entityTypeName)
+    {
+        var definition = SqlServerResources.LogVectorSearchWithoutApproximate(diagnostics);
+
+        if (diagnostics.ShouldLog(definition))
+        {
+            definition.Log(diagnostics, propertyName, entityTypeName);
+        }
+
+        if (diagnostics.NeedsEventData(definition, out var diagnosticSourceEnabled, out var simpleLogEnabled))
+        {
+            var eventData = new EventData(
+                definition,
+                (d, _) => ((EventDefinition<string, string>)d).GenerateMessage(propertyName, entityTypeName));
+
+            diagnostics.DispatchEventData(definition, eventData, diagnosticSourceEnabled, simpleLogEnabled);
+        }
+    }
 }

src/EFCore.SqlServer/Extensions/SqlServerIndexExtensions.cs

@@ -466,9 +466,7 @@ public static void SetDataCompression(this IMutableIndex index, DataCompressionT
     /// <returns>Whether the index is a vector index.</returns>
     [Experimental(EFDiagnostics.SqlServerVectorSearch)]
     public static bool IsVectorIndex(this IReadOnlyIndex index)
-        => index is RuntimeIndex
-            ? throw new InvalidOperationException(CoreStrings.RuntimeModelMissingData)
-            : index.FindAnnotation(SqlServerAnnotationNames.VectorIndexMetric) is not null;
+        => index.FindAnnotation(SqlServerAnnotationNames.VectorIndexMetric) is not null;
 
     /// <summary>
     ///     Returns the similarity metric for the vector index.
@@ -477,9 +475,7 @@ public static bool IsVectorIndex(this IReadOnlyIndex index)
     /// <returns>The similarity metric for the vector index.</returns>
     [Experimental(EFDiagnostics.SqlServerVectorSearch)]
     public static string? GetVectorMetric(this IReadOnlyIndex index)
-        => index is RuntimeIndex
-            ? throw new InvalidOperationException(CoreStrings.RuntimeModelMissingData)
-            : (string?)index[SqlServerAnnotationNames.VectorIndexMetric];
+        => (string?)index[SqlServerAnnotationNames.VectorIndexMetric];
 
     /// <summary>
     ///     Returns the similarity metric for the vector index.
@@ -490,11 +486,6 @@ public static bool IsVectorIndex(this IReadOnlyIndex index)
     [Experimental(EFDiagnostics.SqlServerVectorSearch)]
     public static string? GetVectorMetric(this IReadOnlyIndex index, in StoreObjectIdentifier storeObject)
     {
-        if (index is RuntimeIndex)
-        {
-            throw new InvalidOperationException(CoreStrings.RuntimeModelMissingData);
-        }
-
         var annotation = index.FindAnnotation(SqlServerAnnotationNames.VectorIndexMetric);
         if (annotation != null)
         {
@@ -551,9 +542,7 @@ public static void SetVectorMetric(this IMutableIndex index, string? metric)
     /// <returns>The type of the vector index.</returns>
     [Experimental(EFDiagnostics.SqlServerVectorSearch)]
     public static string? GetVectorIndexType(this IReadOnlyIndex index)
-        => (index is RuntimeIndex)
-            ? throw new InvalidOperationException(CoreStrings.RuntimeModelMissingData)
-            : (string?)index[SqlServerAnnotationNames.VectorIndexType];
+        => (string?)index[SqlServerAnnotationNames.VectorIndexType];
 
     /// <summary>
     ///     Returns the type of the vector index.
@@ -564,11 +553,6 @@ public static void SetVectorMetric(this IMutableIndex index, string? metric)
     [Experimental(EFDiagnostics.SqlServerVectorSearch)]
     public static string? GetVectorIndexType(this IReadOnlyIndex index, in StoreObjectIdentifier storeObject)
     {
-        if (index is RuntimeIndex)
-        {
-            throw new InvalidOperationException(CoreStrings.RuntimeModelMissingData);
-        }
-
         var annotation = index.FindAnnotation(SqlServerAnnotationNames.VectorIndexType);
         if (annotation != null)
         {

src/EFCore.SqlServer/Extensions/SqlServerQueryableExtensions.cs

@@ -18,7 +18,7 @@ public static class SqlServerQueryableExtensions
     #region VectorSearch
 
     /// <summary>
-    ///     Search for vectors similar to a given query vector using an approximate nearest neighbors vector search algorithm.
+    ///     Search for vectors similar to a given query vector using the SQL Server <c>VECTOR_SEARCH()</c> function.
     /// </summary>
     /// <param name="source">The <see cref="DbSet{T}" /> representing the table containing the vector column to query.</param>
     /// <param name="vectorPropertySelector">A selector for the vector property on the entity.</param>
@@ -30,8 +30,9 @@ public static class SqlServerQueryableExtensions
     /// </param>
     /// <remarks>
     ///     <para>
-    ///         Compose the returned query with <c>OrderBy(r => r.Distance)</c> and <c>Take(...)</c> to limit the results as required
-    ///         for approximate vector search.
+    ///         Use <see cref="WithApproximate{T}" /> after <c>Take(...)</c> to enable approximate nearest neighbor (ANN)
+    ///         search, which uses the vector index for better performance. Without <c>WithApproximate</c>, an exact k-nearest
+    ///         neighbor (kNN) search is performed. Add an explicit <c>OrderBy</c> to control result ordering.
     ///     </para>
     /// </remarks>
     /// <seealso href="https://learn.microsoft.com/sql/t-sql/functions/vector-search-transact-sql">
@@ -75,6 +76,32 @@ private static IQueryable<VectorSearchResult<T>> VectorSearch<T, TVector>(
         where TVector : unmanaged
         => throw new UnreachableException();
 
+    /// <summary>
+    ///     Enables approximate nearest neighbor (ANN) search for a vector search query. This causes <c>WITH APPROXIMATE</c> to
+    ///     be added to the SQL <c>TOP</c> clause, instructing SQL Server to use the vector index for better performance.
+    /// </summary>
+    /// <remarks>
+    ///     <para>
+    ///         This method must be called after <c>Take(...)</c> to specify the number of results. Without <c>WithApproximate</c>,
+    ///         vector search performs an exact k-nearest neighbor (kNN) search without using the vector index.
+    ///     </para>
+    /// </remarks>
+    /// <seealso href="https://learn.microsoft.com/sql/t-sql/functions/vector-search-transact-sql">
+    ///     SQL Server documentation for <c>VECTOR_SEARCH()</c>.
+    /// </seealso>
+    [Experimental(EFDiagnostics.SqlServerVectorSearch)]
+    public static IQueryable<T> WithApproximate<T>(this IQueryable<T> source)
+    {
+        var queryableSource = (IQueryable)source;
+
+        return queryableSource.Provider is EntityQueryProvider
+            ? queryableSource.Provider.CreateQuery<T>(
+                Expression.Call(
+                    method: new Func<IQueryable<T>, IQueryable<T>>(WithApproximate).Method,
+                    queryableSource.Expression))
+            : throw new InvalidOperationException(CoreStrings.FunctionOnNonEfLinqProvider(nameof(WithApproximate)));
+    }
+
     #endregion VectorSearch
 
     #region Full-text search TVFs

src/EFCore.SqlServer/Properties/SqlServerStrings.resx

@@ -327,6 +327,10 @@
     <value>Savepoints are disabled because Multiple Active Result Sets (MARS) is enabled. If 'SaveChanges' fails, then the transaction cannot be automatically rolled back to a known clean state. Instead, the transaction should be rolled back by the application before retrying 'SaveChanges'. See https://go.microsoft.com/fwlink/?linkid=2149338 for more information and examples. To identify the code which triggers this warning, call 'ConfigureWarnings(w =&gt; w.Throw(SqlServerEventId.SavepointsDisabledBecauseOfMARS))'.</value>
     <comment>Warning SqlServerEventId.SavepointsDisabledBecauseOfMARS</comment>
   </data>
+  <data name="LogVectorSearchWithoutApproximate" xml:space="preserve">
+    <value>The query uses 'VectorSearch' on property '{property}' of entity type '{entityType}', but 'WithApproximate()' was not specified. The query will perform an exact brute-force search instead of using a vector index. Call 'WithApproximate()' after 'Take()' to use the vector index for better performance. To identify the code which triggers this warning, call 'ConfigureWarnings(w =&gt; w.Throw(SqlServerEventId.VectorSearchWithoutApproximateWarning))'.</value>
+    <comment>Warning SqlServerEventId.VectorSearchWithoutApproximateWarning string string</comment>
+  </data>
   <data name="MultipleIdentityColumns" xml:space="preserve">
     <value>The properties {properties} are configured to use 'Identity' value generation and are mapped to the same table '{table}', but only one column per table can be configured as 'Identity'. Call 'ValueGeneratedNever' in 'OnModelCreating' for properties that should not use 'Identity'.</value>
   </data>
@@ -426,4 +430,10 @@
   <data name="VectorSearchRequiresColumn" xml:space="preserve">
     <value>VectorSearch() requires a valid vector column.</value>
   </data>
+  <data name="WithApproximateRequiresTake" xml:space="preserve">
+    <value>WithApproximate() must be called after Take() to specify the number of results.</value>
+  </data>
+  <data name="WithApproximateNotSupportedWithSkipAndTake" xml:space="preserve">
+    <value>WithApproximate() after Skip().Take() is not supported. Use Take().WithApproximate().Skip() instead, or remove Skip().</value>
+  </data>
 </root>