Throw when deriving from an owned type.

Fixes #17429

src/EFCore/Metadata/Internal/InternalModelBuilder.cs

@@ -82,12 +82,25 @@ private InternalEntityTypeBuilder Entity(
             }
 
             if (shouldBeOwned == true
-                && entityType != null
-                && !entityType.IsOwned()
-                && configurationSource == ConfigurationSource.Explicit
-                && entityType.GetConfigurationSource() == ConfigurationSource.Explicit)
+                && entityType != null)
             {
-                throw new InvalidOperationException(CoreStrings.ClashingNonOwnedEntityType(entityType.DisplayName()));
+                if (!entityType.IsOwned()
+                    && configurationSource == ConfigurationSource.Explicit
+                    && entityType.GetConfigurationSource() == ConfigurationSource.Explicit)
+                {
+                    throw new InvalidOperationException(CoreStrings.ClashingNonOwnedEntityType(entityType.DisplayName()));
+                }
+
+                foreach (var derivedType in entityType.GetDerivedTypes())
+                {
+                    if (!derivedType.IsOwned()
+                        && configurationSource == ConfigurationSource.Explicit
+                        && derivedType.GetConfigurationSource() == ConfigurationSource.Explicit)
+                    {
+                        throw new InvalidOperationException(
+                            CoreStrings.ClashingNonOwnedDerivedEntityType(entityType.DisplayName(), derivedType.DisplayName()));
+                    }
+                }
             }
 
             if (entityType != null)

src/EFCore/Properties/CoreStrings.resx

@@ -1219,4 +1219,7 @@
     <value>'{principalEntityType}.{principalNavigation}' may still be null at runtime despite being declared as non-nullable since only the navigation to principal can be configured as required.</value>
     <comment>Debug CoreEventId.NonNullableReferenceOnDependent string string</comment>
   </data>
-</root>
+  <data name="ClashingNonOwnedDerivedEntityType" xml:space="preserve">
+    <value>The type '{entityType}' cannot be marked as owned because the derived entity type - '{derivedType}' has been configured as non-owned.</value>
+  </data>
+</root>

test/EFCore.Tests/ModelBuilding/ModelBuilderTestBase.cs

@@ -157,12 +157,7 @@ public abstract TestModelBuilder Entity<TEntity>(Action<TestEntityTypeBuilder<TE
             public abstract TestModelBuilder Ignore<TEntity>()
                 where TEntity : class;
 
-            public virtual TestModelBuilder FinalizeModel()
-            {
-                ModelBuilder.FinalizeModel();
-
-                return this;
-            }
+            public virtual IModel FinalizeModel() => ModelBuilder.FinalizeModel();
 
             public virtual string GetDisplayName(Type entityType) => entityType.Name;
 

test/EFCore.Tests/ModelBuilding/OwnedTypesTestBase.cs

@@ -1129,6 +1129,75 @@ public virtual void Reconfiguring_owned_type_as_non_owned_throws()
                             modelBuilder.Entity<SpecialCustomer>().HasOne(c => c.Details)).Message);
             }
 
+            [ConditionalFact]
+            public virtual void Deriving_from_owned_type_throws()
+            {
+                var modelBuilder = CreateModelBuilder();
+
+                modelBuilder.Entity<Book>()
+                    .Ignore(b => b.AlternateLabel)
+                    .Ignore(b => b.Details)
+                    .OwnsOne(b => b.Label, lb =>
+                    {
+                        lb.Ignore(l => l.AnotherBookLabel);
+                        lb.Ignore(l => l.SpecialBookLabel);
+                    });
+
+                Assert.Equal(
+                    CoreStrings.ClashingOwnedEntityType(nameof(AnotherBookLabel)),
+                    Assert.Throws<InvalidOperationException>(
+                        () => modelBuilder.Entity<AnotherBookLabel>()).Message);
+            }
+
+            [ConditionalFact]
+            public virtual void Configuring_base_type_as_owned_throws()
+            {
+                var modelBuilder = CreateModelBuilder();
+
+                modelBuilder.Entity<AnotherBookLabel>();
+
+                modelBuilder.Entity<Book>()
+                    .Ignore(b => b.AlternateLabel)
+                    .Ignore(b => b.Details);
+
+                Assert.Equal(
+                    CoreStrings.ClashingNonOwnedDerivedEntityType(nameof(BookLabel), nameof(AnotherBookLabel)),
+                    Assert.Throws<InvalidOperationException>(
+                        () =>
+                            modelBuilder.Entity<Book>().OwnsOne(c => c.Label)).Message);
+            }
+
+            [ConditionalFact]
+            public virtual void CLR_base_type_can_be_owned_when_not_in_hierarchy()
+            {
+                var modelBuilder = CreateModelBuilder();
+
+                modelBuilder.Entity<AnotherBookLabel>()
+                    .HasBaseType(null)
+                    .Ignore(l => l.Book)
+                    .Ignore(l => l.SpecialBookLabel)
+                    .Ignore(l => l.AnotherBookLabel);
+
+                modelBuilder.Entity<Book>()
+                    .Ignore(b => b.AlternateLabel)
+                    .Ignore(b => b.Details)
+                    .OwnsOne(c => c.Label, lb =>
+                        {
+                            lb.Ignore(l => l.AnotherBookLabel);
+                            lb.Ignore(l => l.SpecialBookLabel);
+                        });
+
+                var model = modelBuilder.FinalizeModel();
+
+                var bookLabelOwnership = model.FindEntityType(typeof(Book)).FindNavigation(nameof(Book.Label))
+                    .ForeignKey;
+
+                Assert.True(bookLabelOwnership.IsOwnership);
+                Assert.Equal(nameof(BookLabel.Book), bookLabelOwnership.DependentToPrincipal.Name);
+
+                Assert.Null(model.FindEntityType(typeof(AnotherBookLabel)).BaseType);
+            }
+
             [ConditionalFact]
             public virtual void OwnedType_can_derive_from_Collection()
             {