Metadata: Add metadata support for shared entity type

src/EFCore/Extensions/EntityTypeExtensions.cs

@@ -292,7 +292,7 @@ public static IEnumerable<IIndex> GetDeclaredIndexes([NotNull] this IEntityType
             => entityType.AsEntityType().GetDeclaredIndexes();
 
         private static string DisplayNameDefault(this ITypeBase type)
-            => type.ClrType != null
+            => type.ClrType != null && !type.IsSharedType
                 ? type.ClrType.ShortDisplayName()
                 : type.Name;
 
@@ -345,7 +345,7 @@ public static string DisplayName([NotNull] this ITypeBase type)
         [DebuggerStepThrough]
         public static string ShortName([NotNull] this ITypeBase type)
         {
-            if (type.ClrType != null)
+            if (type.ClrType != null && !type.IsSharedType)
             {
                 return type.ClrType.ShortDisplayName();
             }

src/EFCore/Metadata/IConventionModel.cs

@@ -49,6 +49,15 @@ public interface IConventionModel : IModel, IConventionAnnotatable
         /// <returns> The new entity type. </returns>
         IConventionEntityType AddEntityType([NotNull] Type clrType, bool fromDataAnnotation = false);
 
+        /// <summary>
+        ///     Adds an entity type to the model.
+        /// </summary>
+        /// <param name="name"> The name of the entity to be added. </param>
+        /// <param name="clrType"> The CLR class that is used to represent instances of the entity type. </param>
+        /// <param name="fromDataAnnotation"> Indicates whether the configuration was specified using a data annotation. </param>
+        /// <returns> The new entity type. </returns>
+        IConventionEntityType AddEntityType([NotNull] string name, [NotNull] Type clrType, bool fromDataAnnotation = false);
+
         /// <summary>
         ///     Adds an entity type with a defining navigation to the model.
         /// </summary>

src/EFCore/Metadata/IMutableModel.cs

@@ -41,6 +41,14 @@ public interface IMutableModel : IModel, IMutableAnnotatable
         /// <returns> The new entity type. </returns>
         IMutableEntityType AddEntityType([NotNull] Type clrType);
 
+        /// <summary>
+        ///     Adds an entity type to the model.
+        /// </summary>
+        /// <param name="name"> The name of the entity to be added. </param>
+        /// <param name="clrType"> The CLR class that is used to represent instances of the entity type. </param>
+        /// <returns> The new entity type. </returns>
+        IMutableEntityType AddEntityType([NotNull] string name, [NotNull] Type clrType);
+
         /// <summary>
         ///     Adds an entity type with a defining navigation to the model.
         /// </summary>

src/EFCore/Metadata/ITypeBase.cs

@@ -32,5 +32,10 @@ public interface ITypeBase : IAnnotatable
         ///     </para>
         /// </summary>
         Type ClrType { get; }
+
+        /// <summary>
+        ///     Gets whether this entity type can share its ClrType with other entities.
+        /// </summary>
+        bool IsSharedType { get; }
     }
 }

src/EFCore/Metadata/Internal/EntityType.cs

@@ -98,6 +98,24 @@ public EntityType([NotNull] Type clrType, [NotNull] Model model, ConfigurationSo
             Builder = new InternalEntityTypeBuilder(this, model.Builder);
         }
 
+        /// <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 EntityType([NotNull] string name, [NotNull] Type clrType, [NotNull] Model model, ConfigurationSource configurationSource)
+            : base(name, clrType, model, configurationSource)
+        {
+            if (!clrType.IsValidEntityType())
+            {
+                throw new ArgumentException(CoreStrings.InvalidEntityType(clrType));
+            }
+
+            _properties = new SortedDictionary<string, Property>(new PropertyNameComparer(this));
+            Builder = new InternalEntityTypeBuilder(this, model.Builder);
+        }
+
         /// <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

src/EFCore/Metadata/Internal/Model.cs

@@ -52,6 +52,8 @@ private readonly SortedDictionary<string, SortedSet<EntityType>> _entityTypesWit
         private readonly Dictionary<string, ConfigurationSource> _ignoredTypeNames
             = new Dictionary<string, ConfigurationSource>(StringComparer.Ordinal);
 
+        private readonly HashSet<Type> _sharedEntityClrTypes = new HashSet<Type>();
+
         /// <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
@@ -146,6 +148,25 @@ public virtual EntityType AddEntityType(
             return AddEntityType(entityType);
         }
 
+        /// <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 virtual EntityType AddEntityType(
+            [NotNull] string name,
+            [NotNull] Type type,
+            ConfigurationSource configurationSource)
+        {
+            Check.NotEmpty(name, nameof(name));
+            Check.NotNull(type, nameof(type));
+
+            var entityType = new EntityType(name, type, this, configurationSource);
+
+            return AddEntityType(entityType);
+        }
+
         private EntityType AddEntityType(EntityType entityType)
         {
             var entityTypeName = entityType.Name;
@@ -193,6 +214,15 @@ private EntityType AddEntityType(EntityType entityType)
                     throw new InvalidOperationException(CoreStrings.DuplicateEntityType(entityType.DisplayName()));
                 }
 
+                if (entityType.IsSharedType)
+                {
+                    _sharedEntityClrTypes.Add(entityType.ClrType);
+                }
+                else if (_sharedEntityClrTypes.Contains(entityType.ClrType))
+                {
+                    throw new InvalidOperationException(CoreStrings.ClashingSharedType(entityType.DisplayName()));
+                }
+
                 _entityTypes.Add(entityTypeName, entityType);
             }
 
@@ -206,7 +236,14 @@ private EntityType AddEntityType(EntityType entityType)
         ///     doing so can result in application failures when updating to a new Entity Framework Core release.
         /// </summary>
         public virtual EntityType FindEntityType([NotNull] Type type)
-            => FindEntityType(GetDisplayName(type));
+        {
+            if (_sharedEntityClrTypes.Contains(type))
+            {
+                throw new InvalidOperationException(CoreStrings.CannotFindEntityWithClrTypeWhenShared(type.DisplayName()));
+            }
+
+            return FindEntityType(GetDisplayName(type));
+        }
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
@@ -905,6 +942,14 @@ public virtual DebugView DebugView
         /// </summary>
         IMutableEntityType IMutableModel.AddEntityType(Type type) => AddEntityType(type, ConfigurationSource.Explicit);
 
+        /// <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>
+        IMutableEntityType IMutableModel.AddEntityType(string name, Type type) => AddEntityType(name, type, ConfigurationSource.Explicit);
+
         /// <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
@@ -981,7 +1026,8 @@ void IMutableModel.AddIgnored(string name)
         /// </summary>
         IConventionModelBuilder IConventionModel.Builder
         {
-            [DebuggerStepThrough] get => Builder;
+            [DebuggerStepThrough]
+            get => Builder;
         }
 
         /// <summary>
@@ -1020,6 +1066,15 @@ IConventionEntityType IConventionModel.AddEntityType(string name, bool fromDataA
         IConventionEntityType IConventionModel.AddEntityType(Type clrType, bool fromDataAnnotation)
             => AddEntityType(clrType, fromDataAnnotation ? ConfigurationSource.DataAnnotation : ConfigurationSource.Convention);
 
+        /// <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>
+        IConventionEntityType IConventionModel.AddEntityType(string name, Type clrType, bool fromDataAnnotation)
+            => AddEntityType(name, clrType, fromDataAnnotation ? ConfigurationSource.DataAnnotation : ConfigurationSource.Convention);
+
         /// <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

src/EFCore/Metadata/Internal/TypeBase.cs

@@ -44,6 +44,7 @@ protected TypeBase([NotNull] string name, [NotNull] Model model, ConfigurationSo
             Check.NotNull(model, nameof(model));
 
             Name = name;
+            IsSharedType = false;
         }
 
         /// <summary>
@@ -59,6 +60,25 @@ protected TypeBase([NotNull] Type clrType, [NotNull] Model model, ConfigurationS
 
             Name = model.GetDisplayName(clrType);
             ClrType = clrType;
+            IsSharedType = false;
+        }
+
+        /// <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 TypeBase([NotNull] string name, [NotNull] Type clrType, [NotNull] Model model, ConfigurationSource configurationSource)
+            : this(model, configurationSource)
+        {
+            Check.NotEmpty(name, nameof(name));
+            Check.NotNull(clrType, nameof(clrType));
+            Check.NotNull(model, nameof(model));
+
+            Name = name;
+            ClrType = clrType;
+            IsSharedType = true;
         }
 
         private TypeBase([NotNull] Model model, ConfigurationSource configurationSource)
@@ -91,6 +111,14 @@ private TypeBase([NotNull] Model model, ConfigurationSource configurationSource)
         /// </summary>
         public virtual string Name { [DebuggerStepThrough] get; }
 
+        /// <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 virtual bool IsSharedType { [DebuggerStepThrough] get; }
+
         /// <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

src/EFCore/Properties/CoreStrings.resx

@@ -1260,4 +1260,10 @@
   <data name="BackingFieldOnIndexer" xml:space="preserve">
     <value>Cannot set backing field '{field}' for the indexer property '{entityType}.{property}'. Indexer properties are not allowed to use a backing field.</value>
   </data>
+  <data name="ClashingSharedType" xml:space="preserve">
+    <value>The entity type '{entityType}' cannot be added to the model because a shared entity type with the same clr type already exists.</value>
+  </data>
+  <data name="CannotFindEntityWithClrTypeWhenShared" xml:space="preserve">
+    <value>Cannot find entity type with type '{clrType}' since model contains shared entity type(s) with same type.</value>
+  </data>
 </root>

test/EFCore.Tests/Metadata/Internal/EntityTypeTest.cs

@@ -64,6 +64,7 @@ private class FakeEntityType : IEntityType
             public IEnumerable<IAnnotation> GetAnnotations() => throw new NotImplementedException();
             public IModel Model { get; }
             public string Name { get; }
+            public bool IsSharedType { get; }
             public Type ClrType { get; }
             public IEntityType BaseType { get; }
             public string DefiningNavigationName { get; }
@@ -102,6 +103,10 @@ public void Display_name_is_entity_type_name_when_no_CLR_type()
                 "Everything.Is+Awesome<When.We, re.Living<Our.Dream>>",
                 CreateModel().AddEntityType("Everything.Is+Awesome<When.We, re.Living<Our.Dream>>").DisplayName());
 
+        [ConditionalFact]
+        public void Display_name_is_entity_type_name_when_shared_entity_type()
+            => Assert.Equal("PostTag", CreateModel().AddEntityType("PostTag", typeof(Dictionary<string, object>)).DisplayName());
+
         [ConditionalFact]
         public void Name_is_prettified_CLR_full_name()
         {

test/EFCore.Tests/Metadata/Internal/ModelTest.cs

@@ -106,10 +106,41 @@ public void Can_add_and_remove_entity_by_name()
             Assert.Null(((EntityType)entityType).Builder);
         }
 
+        [ConditionalFact]
+        public void Can_add_and_remove_shared_entity()
+        {
+            var model = CreateModel();
+            var entityTypeName = "SharedCustomer1";
+            Assert.Null(model.FindEntityType(typeof(Customer)));
+            Assert.Null(model.FindEntityType(entityTypeName));
+
+            var entityType = model.AddEntityType(entityTypeName, typeof(Customer));
+
+            Assert.Equal(typeof(Customer), entityType.ClrType);
+            Assert.Equal(entityTypeName, entityType.Name);
+            Assert.NotNull(model.FindEntityType(entityTypeName));
+            Assert.Same(model, entityType.Model);
+            Assert.NotNull(((EntityType)entityType).Builder);
+
+            Assert.Same(entityType, model.FindEntityType(entityTypeName));
+            Assert.Equal(
+                CoreStrings.CannotFindEntityWithClrTypeWhenShared(typeof(Customer).DisplayName()),
+                Assert.Throws<InvalidOperationException>(
+                    () => model.FindEntityType(typeof(Customer))).Message);
+
+            Assert.Equal(new[] { entityType }, model.GetEntityTypes().ToArray());
+
+            Assert.Same(entityType, model.RemoveEntityType(entityType.Name));
+
+            Assert.Null(model.RemoveEntityType(entityType.Name));
+            Assert.Null(model.FindEntityType(entityTypeName));
+            Assert.Null(((EntityType)entityType).Builder);
+        }
+
         [ConditionalFact]
         public void Can_add_weak_entity_types()
         {
-            IMutableModel model = CreateModel();
+            var model = CreateModel();
             var customerType = model.AddEntityType(typeof(Customer));
             var idProperty = customerType.AddProperty(Customer.IdProperty);
             var customerKey = customerType.AddKey(idProperty);