Allow discriminator properties to have value converter and comparer

src/EFCore.Cosmos/Query/Internal/SqlExpressionFactory.cs

@@ -533,10 +533,11 @@ private void AddDiscriminator(SelectExpression selectExpression, IEntityType ent
             if (concreteEntityTypes.Count == 1)
             {
                 var concreteEntityType = concreteEntityTypes[0];
-                if (concreteEntityType.GetDiscriminatorProperty() != null)
+                var discriminatorProperty = concreteEntityType.GetDiscriminatorProperty();
+                if (discriminatorProperty != null)
                 {
                     var discriminatorColumn = ((EntityProjectionExpression)selectExpression.GetMappedProjection(new ProjectionMember()))
-                        .BindProperty(concreteEntityType.GetDiscriminatorProperty(), clientEval: false);
+                        .BindProperty(discriminatorProperty, clientEval: false);
 
                     selectExpression.ApplyPredicate(
                         Equal((SqlExpression)discriminatorColumn, Constant(concreteEntityType.GetDiscriminatorValue())));

src/EFCore.InMemory/Query/Internal/InMemoryExpressionTranslatingExpressionVisitor.cs

@@ -965,16 +965,17 @@ protected override Expression VisitTypeBinary(TypeBinaryExpression typeBinaryExp
                 {
                     var discriminatorProperty = entityType.GetDiscriminatorProperty();
                     var boundProperty = BindProperty(entityReferenceExpression, discriminatorProperty, discriminatorProperty.ClrType);
+                    var valueComparer = discriminatorProperty.GetKeyValueComparer();
 
-                    var equals = Expression.Equal(
+                    var equals = valueComparer.ExtractEqualsBody(
                         boundProperty,
                         Expression.Constant(derivedType.GetDiscriminatorValue(), discriminatorProperty.ClrType));
 
                     foreach (var derivedDerivedType in derivedType.GetDerivedTypes())
                     {
                         equals = Expression.OrElse(
                             equals,
-                            Expression.Equal(
+                            valueComparer.ExtractEqualsBody(
                                 boundProperty,
                                 Expression.Constant(derivedDerivedType.GetDiscriminatorValue(), discriminatorProperty.ClrType)));
                     }

src/EFCore.InMemory/Query/Internal/InMemoryQueryExpression.cs

@@ -105,7 +105,10 @@ public InMemoryQueryExpression([NotNull] IEntityType entityType)
             foreach (var derivedEntityType in entityType.GetDerivedTypes())
             {
                 var entityCheck = derivedEntityType.GetConcreteDerivedTypesInclusive()
-                    .Select(e => Equal(readExpressionMap[discriminatorProperty], Constant(e.GetDiscriminatorValue())))
+                    .Select(
+                        e => discriminatorProperty.GetKeyValueComparer().ExtractEqualsBody(
+                            readExpressionMap[discriminatorProperty],
+                            Constant(e.GetDiscriminatorValue(), discriminatorProperty.ClrType)))
                     .Aggregate((l, r) => OrElse(l, r));
 
                 foreach (var property in derivedEntityType.GetDeclaredProperties())

src/EFCore/ChangeTracking/ValueComparer.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections;
+using System.Collections.Generic;
 using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
@@ -27,7 +28,7 @@ namespace Microsoft.EntityFrameworkCore.ChangeTracking
     ///         reference.
     ///     </para>
     /// </summary>
-    public abstract class ValueComparer : IEqualityComparer
+    public abstract class ValueComparer : IEqualityComparer, IEqualityComparer<object>
     {
         private protected static readonly MethodInfo _doubleEqualsMethodInfo
             = typeof(double).GetRuntimeMethod(nameof(double.Equals), new[] { typeof(double) });

src/EFCore/Infrastructure/ModelValidator.cs

@@ -638,19 +638,21 @@ protected virtual void ValidateInheritanceMapping(
         /// <param name="rootEntityType"> The entity type to validate. </param>
         protected virtual void ValidateDiscriminatorValues([NotNull] IEntityType rootEntityType)
         {
-            var discriminatorValues = new Dictionary<object, IEntityType>();
             var derivedTypes = rootEntityType.GetDerivedTypesInclusive().ToList();
             if (derivedTypes.Count == 1)
             {
                 return;
             }
 
-            if (rootEntityType.GetDiscriminatorProperty() == null)
+            var discriminatorProperty = rootEntityType.GetDiscriminatorProperty();
+            if (discriminatorProperty == null)
             {
                 throw new InvalidOperationException(
                     CoreStrings.NoDiscriminatorProperty(rootEntityType.DisplayName()));
             }
 
+            var discriminatorValues = new Dictionary<object, IEntityType>(discriminatorProperty.GetKeyValueComparer());
+
             foreach (var derivedType in derivedTypes)
             {
                 if (derivedType.ClrType?.IsInstantiable() != true)

src/EFCore/Query/EntityShaperExpression.cs

@@ -7,9 +7,11 @@
 using System.Linq.Expressions;
 using System.Reflection;
 using JetBrains.Annotations;
+using Microsoft.EntityFrameworkCore.ChangeTracking;
 using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Metadata;
+using Microsoft.EntityFrameworkCore.Query.Internal;
 using Microsoft.EntityFrameworkCore.Storage;
 using Microsoft.EntityFrameworkCore.Utilities;
 
@@ -123,7 +125,26 @@ protected virtual LambdaExpression GenerateMaterializationCondition([NotNull] IE
                             Convert(discriminatorValueVariable, typeof(object)))),
                     Constant(null, typeof(IEntityType)));
 
-                expressions.Add(Switch(discriminatorValueVariable, exception, switchCases));
+
+                var discriminatorComparer = discriminatorProperty.GetKeyValueComparer();
+                if (discriminatorComparer.IsDefault())
+                {
+                    expressions.Add(Switch(discriminatorValueVariable, exception, switchCases));
+                }
+                else
+                {
+                    var staticComparer = typeof(StaticDiscriminatorComparer<,,>).MakeGenericType(
+                        discriminatorProperty.DeclaringEntityType.ClrType,
+                        discriminatorProperty.ClrType,
+                        discriminatorProperty.GetTypeMapping().Converter.ProviderClrType);
+
+                    var comparerField = staticComparer.GetField(nameof(StaticDiscriminatorComparer<int, int, int>.Comparer));
+                    comparerField.SetValue(null, discriminatorComparer);
+
+                    var equalsMethod = staticComparer.GetMethod(nameof(StaticDiscriminatorComparer<int, int, int>.DiscriminatorEquals));
+                    expressions.Add(Switch(discriminatorValueVariable, exception, equalsMethod, switchCases));
+                }
+
                 body = Block(new[] { discriminatorValueVariable }, expressions);
             }
             else

src/EFCore/Query/Internal/StaticDiscriminatorComparer.cs

@@ -0,0 +1,35 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using JetBrains.Annotations;
+using Microsoft.EntityFrameworkCore.ChangeTracking;
+
+namespace Microsoft.EntityFrameworkCore.Query.Internal
+{
+    /// <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>
+    // ReSharper disable twice UnusedTypeParameter
+    public static class StaticDiscriminatorComparer<TEntity, TModel, TProvider>
+    {
+        /// <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 ValueComparer<TModel> Comparer;
+
+        /// <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 bool DiscriminatorEquals([CanBeNull] TModel x, [CanBeNull] TModel y)
+            => Comparer.Equals(x, y);
+    }
+}

test/EFCore.Specification.Tests/GraphUpdates/GraphUpdatesTestBase.cs

@@ -185,8 +185,25 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
                     .HasForeignKey<OptionalSingle2>(e => e.BackId)
                     .OnDelete(DeleteBehavior.SetNull);
 
-                modelBuilder.Entity<OptionalSingle2Derived>();
-                modelBuilder.Entity<OptionalSingle2MoreDerived>();
+                modelBuilder.Entity<OptionalSingle2>(
+                    b =>
+                    {
+                        b.HasDiscriminator(e => e.Disc)
+                            .HasValue<OptionalSingle2>(new MyDiscriminator(1))
+                            .HasValue<OptionalSingle2Derived>(new MyDiscriminator(2))
+                            .HasValue<OptionalSingle2MoreDerived>(new MyDiscriminator(3));
+
+                        b.Property(e => e.Disc)
+                            .HasConversion(
+                                v => v.Value,
+                                v => new MyDiscriminator(v),
+                                new ValueComparer<MyDiscriminator>(
+                                    (l, r) => l.Value == r.Value,
+                                    v => v.Value.GetHashCode(),
+                                    v => new MyDiscriminator(v.Value)))
+                            .Metadata
+                            .SetAfterSaveBehavior(PropertySaveBehavior.Save);
+                    });
 
                 modelBuilder.Entity<RequiredNonPkSingle1>()
                     .HasOne(e => e.Single)
@@ -379,10 +396,6 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
                 modelBuilder.Entity<Produce>()
                     .HasIndex(e => e.BarCode)
                     .IsUnique();
-
-                modelBuilder.Entity<OptionalSingle2Derived>()
-                    .Property<string>("Discriminator")
-                    .Metadata.SetAfterSaveBehavior(PropertySaveBehavior.Save);
             }
 
             protected virtual object CreateFullGraph()
@@ -1692,6 +1705,7 @@ protected class OptionalSingle2 : NotifyingEntity
         {
             private int _id;
             private int? _backId;
+            private MyDiscriminator _disc;
             private OptionalSingle1 _back;
 
             public int Id
@@ -1706,6 +1720,12 @@ public int? BackId
                 set => SetWithNotify(value, ref _backId);
             }
 
+            public MyDiscriminator Disc
+            {
+                get => _disc;
+                set => SetWithNotify(value, ref _disc);
+            }
+
             public OptionalSingle1 Back
             {
                 get => _back;
@@ -1722,6 +1742,20 @@ public override int GetHashCode()
                 => _id;
         }
 
+        protected class MyDiscriminator
+        {
+            public MyDiscriminator(int value)
+                => Value = value;
+
+            public int Value { get; }
+
+            public override bool Equals(object obj)
+                => throw new InvalidOperationException();
+
+            public override int GetHashCode()
+                => throw new InvalidOperationException();
+        }
+
         protected class OptionalSingle2Derived : OptionalSingle2
         {
             public override bool Equals(object obj)

test/EFCore.Specification.Tests/GraphUpdates/GraphUpdatesTestBaseMiscellaneous.cs

@@ -45,23 +45,23 @@ public virtual void Mutating_discriminator_value_can_be_configured_to_allow_muta
                 context =>
                 {
                     var instance = context.Set<OptionalSingle2Derived>().First();
-                    var propertyEntry = context.Entry(instance).Property("Discriminator");
+                    var propertyEntry = context.Entry(instance).Property(e => e.Disc);
                     id = instance.Id;
 
                     Assert.IsType<OptionalSingle2Derived>(instance);
-                    Assert.Equal(nameof(OptionalSingle2Derived), propertyEntry.CurrentValue);
+                    Assert.Equal(2, propertyEntry.CurrentValue.Value);
 
-                    propertyEntry.CurrentValue = nameof(OptionalSingle2);
+                    propertyEntry.CurrentValue = new MyDiscriminator(1);
 
                     context.SaveChanges();
                 },
                 context =>
                 {
                     var instance = context.Set<OptionalSingle2>().First(e => e.Id == id);
-                    var propertyEntry = context.Entry(instance).Property("Discriminator");
+                    var propertyEntry = context.Entry(instance).Property(e => e.Disc);
 
                     Assert.IsType<OptionalSingle2>(instance);
-                    Assert.Equal(nameof(OptionalSingle2), propertyEntry.CurrentValue);
+                    Assert.Equal(1, propertyEntry.CurrentValue.Value);
                 });
         }