Implement EF.Constant

src/EFCore/EF.cs

@@ -63,6 +63,24 @@ public static TProperty Property<TProperty>(
         [NotParameterized] string propertyName)
         => throw new InvalidOperationException(CoreStrings.PropertyMethodInvoked);
 
+    /// <summary>
+    ///     Within the context of an EF LINQ query, forces its argument to be inserted into the query as a constant expression. This can be
+    ///     used to e.g. integrate a value as a constant inside an EF query, instead of as a parameter, for query performance reasons.
+    /// </summary>
+    /// <remarks>
+    ///     <para>
+    ///         Note that this is a static method accessed through the top-level <see cref="EF" /> static type.
+    ///     </para>
+    ///     <para>
+    ///         See <see href="https://aka.ms/efcore-docs-efproperty">Using EF.Property in EF Core queries</see> for more information and examples.
+    ///     </para>
+    /// </remarks>
+    /// <typeparam name="T">The type of the expression to be integrated as a constant into the query.</typeparam>
+    /// <param name="argument">The expression to be integrated as a constant into the query.</param>
+    /// <returns>The same value for further use in the query.</returns>
+    public static T Constant<T>(T argument)
+        => throw new InvalidOperationException(CoreStrings.EFConstantInvoked);
+
     /// <summary>
     ///     Provides CLR methods that get translated to database functions when used in LINQ to Entities queries.
     ///     Calling these methods in other contexts (e.g. LINQ to Objects) will throw a <see cref="NotSupportedException" />.

src/EFCore/Properties/CoreStrings.resx

@@ -474,6 +474,12 @@
   <data name="DuplicateTrigger" xml:space="preserve">
     <value>The trigger '{trigger}' cannot be added to the entity type '{entityType}' because another trigger with the same name already exists on entity type '{conflictingEntityType}'.</value>
   </data>
+  <data name="EFConstantInvoked" xml:space="preserve">
+    <value>The EF.Constant&lt;T&gt; method may only be used within Entity Framework LINQ queries.</value>
+  </data>
+  <data name="EFConstantWithNonEvaluableArgument" xml:space="preserve">
+    <value>The EF.Constant&lt;T&gt; method may only be used with an argument that can be evaluated client-side and does not contain any reference to database-side entities.</value>
+  </data>
   <data name="EmptyComplexType" xml:space="preserve">
     <value>Complex type '{complexType}' has no properties defines. Configure at least one property or don't include this type in the model.</value>
   </data>

src/EFCore/Query/Internal/ParameterExtractingExpressionVisitor.cs

@@ -170,6 +170,31 @@ protected override Expression VisitConditional(ConditionalExpression conditional
             Visit(conditionalExpression.IfFalse));
     }
 
+    /// <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>
+    protected override Expression VisitMethodCall(MethodCallExpression methodCallExpression)
+    {
+        if (methodCallExpression.Method.DeclaringType == typeof(EF) && methodCallExpression.Method.Name == nameof(EF.Constant))
+        {
+            // If this is a call to EF.Constant(), then examine its operand. If the operand isn't evaluatable (i.e. contains a reference
+            // to a database table), throw immediately.
+            // Otherwise, evaluate the operand as a constant and return that.
+            var operand = methodCallExpression.Arguments[0];
+            if (!_evaluatableExpressions.TryGetValue(operand, out _))
+            {
+                throw new InvalidOperationException(CoreStrings.EFConstantWithNonEvaluableArgument);
+            }
+
+            return Evaluate(operand, generateParameter: false);
+        }
+
+        return base.VisitMethodCall(methodCallExpression);
+    }
+
     /// <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
@@ -655,6 +680,16 @@ private static bool IsEvaluatableNodeType(Expression expression, out bool prefer
                     preferNoEvaluation = false;
                     return expression.CanReduce && IsEvaluatableNodeType(expression.ReduceAndCheck(), out preferNoEvaluation);
 
+                // Identify a call to EF.Constant(), and flag that as non-evaluable.
+                // This is important to prevent a larger subtree containing EF.Constant from being evaluated, i.e. to make sure that
+                // the EF.Function argument is present in the tree as its own, constant node.
+                case ExpressionType.Call
+                    when expression is MethodCallExpression { Method: var method }
+                    && method.DeclaringType == typeof(EF)
+                    && method.Name == nameof(EF.Constant):
+                    preferNoEvaluation = true;
+                    return false;
+
                 default:
                     preferNoEvaluation = false;
                     return true;

test/EFCore.Cosmos.FunctionalTests/Query/NorthwindWhereQueryCosmosTest.cs

@@ -2903,6 +2903,49 @@ FROM root c
 """);
     }
 
+    public override async Task EF_Constant(bool async)
+    {
+        await base.EF_Constant(async);
+
+        AssertSql(
+            """
+SELECT c
+FROM root c
+WHERE ((c["Discriminator"] = "Customer") AND (c["CustomerID"] = "ALFKI"))
+""");
+    }
+
+    public override async Task EF_Constant_with_subtree(bool async)
+    {
+        await base.EF_Constant_with_subtree(async);
+
+        AssertSql(
+            """
+SELECT c
+FROM root c
+WHERE ((c["Discriminator"] = "Customer") AND (c["CustomerID"] = "ALFKI"))
+""");
+    }
+
+    public override async Task EF_Constant_does_not_parameterized_as_part_of_bigger_subtree(bool async)
+    {
+        await base.EF_Constant_does_not_parameterized_as_part_of_bigger_subtree(async);
+
+        AssertSql(
+            """
+SELECT c
+FROM root c
+WHERE ((c["Discriminator"] = "Customer") AND (c["CustomerID"] = ("ALF" || "KI")))
+""");
+    }
+
+    public override async Task EF_Constant_with_non_evaluatable_argument_throws(bool async)
+    {
+        await base.EF_Constant_with_non_evaluatable_argument_throws(async);
+
+        AssertSql();
+    }
+
     private void AssertSql(params string[] expected)
         => Fixture.TestSqlLoggerFactory.AssertBaseline(expected);
 

test/EFCore.Specification.Tests/Query/NorthwindWhereQueryTestBase.cs

@@ -3,9 +3,11 @@
 
 using Microsoft.EntityFrameworkCore.TestModels.Northwind;
 
+namespace Microsoft.EntityFrameworkCore.Query;
+
+// ReSharper disable ConvertToConstant.Local
 // ReSharper disable RedundantBoolCompare
 // ReSharper disable InconsistentNaming
-namespace Microsoft.EntityFrameworkCore.Query;
 
 public abstract class NorthwindWhereQueryTestBase<TFixture> : QueryTestBase<TFixture>
     where TFixture : NorthwindQueryFixtureBase<NoopModelCustomizer>, new()
@@ -2342,4 +2344,53 @@ public virtual Task Case_block_simplification_works_correctly(bool async)
             async,
             ss => ss.Set<Customer>().Where(c => (c.Region == null ? "OR" : c.Region) == "OR"));
 #pragma warning restore IDE0029 // Use coalesce expression
+
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task EF_Constant(bool async)
+    {
+        var id = "ALFKI";
+
+        return AssertQuery(
+            async,
+            ss => ss.Set<Customer>().Where(c => c.CustomerID == EF.Constant(id)),
+            ss => ss.Set<Customer>().Where(c => c.CustomerID == "ALFKI"));
+    }
+
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task EF_Constant_with_subtree(bool async)
+    {
+        var i = "ALF";
+        var j = "KI";
+
+        return AssertQuery(
+            async,
+            ss => ss.Set<Customer>().Where(c => c.CustomerID == EF.Constant(i + j)),
+            ss => ss.Set<Customer>().Where(c => c.CustomerID == "ALFKI"));
+    }
+
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task EF_Constant_does_not_parameterized_as_part_of_bigger_subtree(bool async)
+    {
+        var id = "ALF";
+
+        return AssertQuery(
+            async,
+            ss => ss.Set<Customer>().Where(c => c.CustomerID == EF.Constant(id) + "KI"),
+            ss => ss.Set<Customer>().Where(c => c.CustomerID == "ALF" + "KI"));
+    }
+
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual async Task EF_Constant_with_non_evaluatable_argument_throws(bool async)
+    {
+        var exception = await Assert.ThrowsAsync<InvalidOperationException>(
+            () => AssertQuery(
+                async,
+                ss => ss.Set<Customer>().Where(c => c.CustomerID == EF.Constant(c.CustomerID))));
+
+        Assert.Equal(CoreStrings.EFConstantWithNonEvaluableArgument, exception.Message);
+    }
 }

test/EFCore.Specification.Tests/Query/PrimitiveCollectionsQueryTestBase.cs

@@ -92,6 +92,18 @@ public virtual Task Inline_collection_Contains_with_three_values(bool async)
             async,
             ss => ss.Set<PrimitiveCollectionsEntity>().Where(c => new[] { 2, 999, 1000 }.Contains(c.Id)));
 
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task Inline_collection_Contains_with_EF_Constant(bool async)
+    {
+        var ids = new[] { 2, 999, 1000 };
+
+        return AssertQuery(
+            async,
+            ss => ss.Set<PrimitiveCollectionsEntity>().Where(c => EF.Constant(ids).Contains(c.Id)),
+            ss => ss.Set<PrimitiveCollectionsEntity>().Where(c => new[] { 2, 99, 1000 }.Contains(c.Id)));
+    }
+
     [ConditionalTheory]
     [MemberData(nameof(IsAsyncData))]
     public virtual Task Inline_collection_Contains_with_all_parameters(bool async)

test/EFCore.SqlServer.FunctionalTests/Query/NorthwindWhereQuerySqlServerTest.cs

@@ -3243,6 +3243,49 @@ public override async Task Where_client_deep_inside_predicate_and_server_top_lev
         AssertSql();
     }
 
+    public override async Task EF_Constant(bool async)
+    {
+        await base.EF_Constant(async);
+
+        AssertSql(
+            """
+SELECT [c].[CustomerID], [c].[Address], [c].[City], [c].[CompanyName], [c].[ContactName], [c].[ContactTitle], [c].[Country], [c].[Fax], [c].[Phone], [c].[PostalCode], [c].[Region]
+FROM [Customers] AS [c]
+WHERE [c].[CustomerID] = N'ALFKI'
+""");
+    }
+
+    public override async Task EF_Constant_with_subtree(bool async)
+    {
+        await base.EF_Constant_with_subtree(async);
+
+        AssertSql(
+            """
+SELECT [c].[CustomerID], [c].[Address], [c].[City], [c].[CompanyName], [c].[ContactName], [c].[ContactTitle], [c].[Country], [c].[Fax], [c].[Phone], [c].[PostalCode], [c].[Region]
+FROM [Customers] AS [c]
+WHERE [c].[CustomerID] = N'ALFKI'
+""");
+    }
+
+    public override async Task EF_Constant_does_not_parameterized_as_part_of_bigger_subtree(bool async)
+    {
+        await base.EF_Constant_does_not_parameterized_as_part_of_bigger_subtree(async);
+
+        AssertSql(
+            """
+SELECT [c].[CustomerID], [c].[Address], [c].[City], [c].[CompanyName], [c].[ContactName], [c].[ContactTitle], [c].[Country], [c].[Fax], [c].[Phone], [c].[PostalCode], [c].[Region]
+FROM [Customers] AS [c]
+WHERE [c].[CustomerID] = N'ALF' + N'KI'
+""");
+    }
+
+    public override async Task EF_Constant_with_non_evaluatable_argument_throws(bool async)
+    {
+        await base.EF_Constant_with_non_evaluatable_argument_throws(async);
+
+        AssertSql();
+    }
+
     private void AssertSql(params string[] expected)
         => Fixture.TestSqlLoggerFactory.AssertBaseline(expected);
 

test/EFCore.SqlServer.FunctionalTests/Query/PrimitiveCollectionsQueryOldSqlServerTest.cs

@@ -150,6 +150,18 @@ WHERE [p].[Id] IN (2, 999, 1000)
 """);
     }
 
+    public override async Task Inline_collection_Contains_with_EF_Constant(bool async)
+    {
+        await base.Inline_collection_Contains_with_EF_Constant(async);
+
+        AssertSql(
+            """
+SELECT [p].[Id], [p].[Bool], [p].[Bools], [p].[DateTime], [p].[DateTimes], [p].[Enum], [p].[Enums], [p].[Int], [p].[Ints], [p].[NullableInt], [p].[NullableInts], [p].[NullableString], [p].[NullableStrings], [p].[String], [p].[Strings]
+FROM [PrimitiveCollectionsEntity] AS [p]
+WHERE [p].[Id] IN (2, 999, 1000)
+""");
+    }
+
     public override async Task Inline_collection_Contains_with_all_parameters(bool async)
     {
         await base.Inline_collection_Contains_with_all_parameters(async);

test/EFCore.SqlServer.FunctionalTests/Query/PrimitiveCollectionsQuerySqlServerTest.cs

@@ -142,6 +142,18 @@ WHERE [p].[Id] IN (2, 999, 1000)
 """);
     }
 
+    public override async Task Inline_collection_Contains_with_EF_Constant(bool async)
+    {
+        await base.Inline_collection_Contains_with_EF_Constant(async);
+
+        AssertSql(
+            """
+SELECT [p].[Id], [p].[Bool], [p].[Bools], [p].[DateTime], [p].[DateTimes], [p].[Enum], [p].[Enums], [p].[Int], [p].[Ints], [p].[NullableInt], [p].[NullableInts], [p].[NullableString], [p].[NullableStrings], [p].[String], [p].[Strings]
+FROM [PrimitiveCollectionsEntity] AS [p]
+WHERE [p].[Id] IN (2, 999, 1000)
+""");
+    }
+
     public override async Task Inline_collection_Contains_with_all_parameters(bool async)
     {
         await base.Inline_collection_Contains_with_all_parameters(async);

test/EFCore.Sqlite.FunctionalTests/Query/PrimitiveCollectionsQuerySqliteTest.cs

@@ -143,6 +143,18 @@ public override async Task Inline_collection_Contains_with_three_values(bool asy
 """);
     }
 
+    public override async Task Inline_collection_Contains_with_EF_Constant(bool async)
+    {
+        await base.Inline_collection_Contains_with_EF_Constant(async);
+
+        AssertSql(
+            """
+SELECT "p"."Id", "p"."Bool", "p"."Bools", "p"."DateTime", "p"."DateTimes", "p"."Enum", "p"."Enums", "p"."Int", "p"."Ints", "p"."NullableInt", "p"."NullableInts", "p"."NullableString", "p"."NullableStrings", "p"."String", "p"."Strings"
+FROM "PrimitiveCollectionsEntity" AS "p"
+WHERE "p"."Id" IN (2, 999, 1000)
+""");
+    }
+
     public override async Task Inline_collection_Contains_with_all_parameters(bool async)
     {
         await base.Inline_collection_Contains_with_all_parameters(async);