Query: Change alias of the column for TPT Discriminator

Feedback of #21784
Part of #21509

src/EFCore.Relational/Metadata/Internal/RelationalEntityTypeExtensions.cs

@@ -33,5 +33,14 @@ public static IEnumerable<ITableMappingBase> GetViewOrTableMappings([NotNull] th
             (IEnumerable<ITableMappingBase>)(entityType[RelationalAnnotationNames.ViewMappings]
                 ?? entityType[RelationalAnnotationNames.TableMappings])
                 ?? Enumerable.Empty<ITableMappingBase>();
+
+        /// <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 IReadOnlyList<string> GetTptDiscriminatorValues([NotNull] this IEntityType entityType)
+            => entityType.GetConcreteDerivedTypesInclusive().Select(et => et.ShortName()).ToList();
     }
 }

src/EFCore.Relational/Query/EntityProjectionExpression.cs

@@ -9,6 +9,7 @@
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.EntityFrameworkCore.Metadata;
+using Microsoft.EntityFrameworkCore.Metadata.Internal;
 using Microsoft.EntityFrameworkCore.Query.SqlExpressions;
 using Microsoft.EntityFrameworkCore.Utilities;
 
@@ -135,8 +136,7 @@ public virtual EntityProjectionExpression UpdateEntityType([NotNull] IEntityType
             var discriminatorExpression = DiscriminatorExpression;
             if (DiscriminatorExpression is CaseExpression caseExpression)
             {
-                var entityTypesToSelect = derivedType.GetDerivedTypesInclusive().Where(et => !et.IsAbstract())
-                    .Select(et => et.ShortName()).ToHashSet();
+                var entityTypesToSelect = derivedType.GetTptDiscriminatorValues();
                 var whenClauses = caseExpression.WhenClauses
                     .Where(wc => entityTypesToSelect.Contains((string)((SqlConstantExpression)wc.Result).Value))
                     .ToList();

src/EFCore.Relational/Query/RelationalQueryableMethodTranslatingExpressionVisitor.cs

@@ -783,8 +783,7 @@ protected override ShapedQueryExpression TranslateOfType(ShapedQueryExpression s
                     if (discriminatorProperty == null)
                     {
                         var selectExpression = (SelectExpression)source.QueryExpression;
-                        var discriminatorValues = derivedType.GetConcreteDerivedTypesInclusive().Where(et => !et.IsAbstract())
-                            .Select(et => et.ShortName()).ToList();
+                        var discriminatorValues = derivedType.GetTptDiscriminatorValues();
                         var projectionBindingExpression = (ProjectionBindingExpression)entityShaperExpression.ValueBufferExpression;
 
                         var projectionMember = projectionBindingExpression.ProjectionMember;

src/EFCore.Relational/Query/RelationalSqlTranslatingExpressionVisitor.cs

@@ -780,12 +780,11 @@ protected override Expression VisitTypeBinary(TypeBinaryExpression typeBinaryExp
                 var derivedType = entityType.GetDerivedTypes().SingleOrDefault(et => et.ClrType == typeBinaryExpression.TypeOperand);
                 if (derivedType != null)
                 {
-                    var concreteEntityTypes = derivedType.GetConcreteDerivedTypesInclusive().ToList();
                     var discriminatorProperty = entityType.GetDiscriminatorProperty();
                     if (discriminatorProperty == null)
                     {
                         // TPT
-                        var discriminatorValues = concreteEntityTypes.Select(et => et.ShortName()).ToList();
+                        var discriminatorValues = derivedType.GetTptDiscriminatorValues();
                         if (entityReferenceExpression.SubqueryEntity != null)
                         {
                             var entityShaper = (EntityShaperExpression)entityReferenceExpression.SubqueryEntity.ShaperExpression;
@@ -839,6 +838,7 @@ SqlExpression GeneratePredicateTPT(EntityProjectionExpression entityProjectionEx
                     }
                     else
                     {
+                        var concreteEntityTypes = derivedType.GetConcreteDerivedTypesInclusive().ToList();
                         var discriminatorColumn = BindProperty(entityReferenceExpression, discriminatorProperty);
                         if (discriminatorColumn != null)
                         {

src/EFCore.Relational/Query/SqlExpressions/SelectExpression.cs

@@ -38,6 +38,8 @@ public sealed class SelectExpression : TableExpressionBase
             { ExpressionType.GreaterThanOrEqual, ExpressionType.LessThanOrEqual },
         };
 
+        private const string DiscriminatorColumnAlias = "Discriminator";
+
         private readonly IDictionary<EntityProjectionExpression, IDictionary<IProperty, int>> _entityProjectionCache
             = new Dictionary<EntityProjectionExpression, IDictionary<IProperty, int>>();
 
@@ -328,7 +330,7 @@ public void ApplyProjection()
 
                     if (entityProjection.DiscriminatorExpression != null)
                     {
-                        AddToProjection(entityProjection.DiscriminatorExpression);
+                        AddToProjection(entityProjection.DiscriminatorExpression, DiscriminatorColumnAlias);
                     }
 
                     result[keyValuePair.Key] = Constant(map);
@@ -443,7 +445,7 @@ public IDictionary<IProperty, int> AddToProjection([NotNull] EntityProjectionExp
 
                 if (entityProjection.DiscriminatorExpression != null)
                 {
-                    AddToProjection(entityProjection.DiscriminatorExpression);
+                    AddToProjection(entityProjection.DiscriminatorExpression, DiscriminatorColumnAlias);
                 }
 
                 _entityProjectionCache[entityProjection] = dictionary;
@@ -933,7 +935,7 @@ void HandleEntityProjection(
                     discriminatorExpression = GenerateDiscriminatorExpression(
                         select1, projection1.DiscriminatorExpression,
                         select2, projection2.DiscriminatorExpression,
-                        "Discriminator");
+                        DiscriminatorColumnAlias);
                 }
 
                 _projectionMapping[projectionMember] = new EntityProjectionExpression(
@@ -1143,7 +1145,7 @@ EntityProjectionExpression LiftEntityProjectionFromSubquery(EntityProjectionExpr
                 ColumnExpression discriminatorExpression = null;
                 if (entityProjection.DiscriminatorExpression != null)
                 {
-                    discriminatorExpression = subquery.GenerateOuterColumn(entityProjection.DiscriminatorExpression);
+                    discriminatorExpression = subquery.GenerateOuterColumn(entityProjection.DiscriminatorExpression, DiscriminatorColumnAlias);
                     projectionMap[entityProjection.DiscriminatorExpression] = discriminatorExpression;
                 }
 

src/EFCore/Metadata/Internal/EntityTypeExtensions.cs

@@ -7,7 +7,6 @@
 using System.Reflection;
 using System.Runtime.CompilerServices;
 using JetBrains.Annotations;
-using Microsoft.EntityFrameworkCore.ChangeTracking;
 using Microsoft.EntityFrameworkCore.ChangeTracking.Internal;
 using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.EntityFrameworkCore.Storage;

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

@@ -22,7 +22,7 @@ public override void Can_use_of_type_animal()
                 @"SELECT [a].[Species], [a].[CountryId], [a].[Name], [b].[EagleId], [b].[IsFlightless], [e].[Group], [k].[FoundOn], CASE
     WHEN [k].[Species] IS NOT NULL THEN N'Kiwi'
     WHEN [e].[Species] IS NOT NULL THEN N'Eagle'
-END
+END AS [Discriminator]
 FROM [Animals] AS [a]
 LEFT JOIN [Birds] AS [b] ON [a].[Species] = [b].[Species]
 LEFT JOIN [Eagle] AS [e] ON [a].[Species] = [e].[Species]
@@ -39,7 +39,7 @@ public override void Can_use_is_kiwi()
                 @"SELECT [a].[Species], [a].[CountryId], [a].[Name], [b].[EagleId], [b].[IsFlightless], [e].[Group], [k].[FoundOn], CASE
     WHEN [k].[Species] IS NOT NULL THEN N'Kiwi'
     WHEN [e].[Species] IS NOT NULL THEN N'Eagle'
-END
+END AS [Discriminator]
 FROM [Animals] AS [a]
 LEFT JOIN [Birds] AS [b] ON [a].[Species] = [b].[Species]
 LEFT JOIN [Eagle] AS [e] ON [a].[Species] = [e].[Species]
@@ -55,7 +55,7 @@ public override void Can_use_is_kiwi_with_other_predicate()
                 @"SELECT [a].[Species], [a].[CountryId], [a].[Name], [b].[EagleId], [b].[IsFlightless], [e].[Group], [k].[FoundOn], CASE
     WHEN [k].[Species] IS NOT NULL THEN N'Kiwi'
     WHEN [e].[Species] IS NOT NULL THEN N'Eagle'
-END
+END AS [Discriminator]
 FROM [Animals] AS [a]
 LEFT JOIN [Birds] AS [b] ON [a].[Species] = [b].[Species]
 LEFT JOIN [Eagle] AS [e] ON [a].[Species] = [e].[Species]
@@ -87,7 +87,7 @@ public override void Can_use_of_type_bird()
                 @"SELECT [a].[Species], [a].[CountryId], [a].[Name], [b].[EagleId], [b].[IsFlightless], [e].[Group], [k].[FoundOn], CASE
     WHEN [k].[Species] IS NOT NULL THEN N'Kiwi'
     WHEN [e].[Species] IS NOT NULL THEN N'Eagle'
-END
+END AS [Discriminator]
 FROM [Animals] AS [a]
 LEFT JOIN [Birds] AS [b] ON [a].[Species] = [b].[Species]
 LEFT JOIN [Eagle] AS [e] ON [a].[Species] = [e].[Species]
@@ -104,7 +104,7 @@ public override void Can_use_of_type_bird_predicate()
                 @"SELECT [a].[Species], [a].[CountryId], [a].[Name], [b].[EagleId], [b].[IsFlightless], [e].[Group], [k].[FoundOn], CASE
     WHEN [k].[Species] IS NOT NULL THEN N'Kiwi'
     WHEN [e].[Species] IS NOT NULL THEN N'Eagle'
-END
+END AS [Discriminator]
 FROM [Animals] AS [a]
 LEFT JOIN [Birds] AS [b] ON [a].[Species] = [b].[Species]
 LEFT JOIN [Eagle] AS [e] ON [a].[Species] = [e].[Species]
@@ -134,7 +134,7 @@ public override void Can_use_of_type_bird_first()
                 @"SELECT TOP(1) [a].[Species], [a].[CountryId], [a].[Name], [b].[EagleId], [b].[IsFlightless], [e].[Group], [k].[FoundOn], CASE
     WHEN [k].[Species] IS NOT NULL THEN N'Kiwi'
     WHEN [e].[Species] IS NOT NULL THEN N'Eagle'
-END
+END AS [Discriminator]
 FROM [Animals] AS [a]
 LEFT JOIN [Birds] AS [b] ON [a].[Species] = [b].[Species]
 LEFT JOIN [Eagle] AS [e] ON [a].[Species] = [e].[Species]
@@ -150,7 +150,7 @@ public override void Can_use_of_type_kiwi()
             AssertSql(
                 @"SELECT [a].[Species], [a].[CountryId], [a].[Name], [b].[EagleId], [b].[IsFlightless], [k].[FoundOn], CASE
     WHEN [k].[Species] IS NOT NULL THEN N'Kiwi'
-END
+END AS [Discriminator]
 FROM [Animals] AS [a]
 LEFT JOIN [Birds] AS [b] ON [a].[Species] = [b].[Species]
 LEFT JOIN [Eagle] AS [e] ON [a].[Species] = [e].[Species]