[6.0] ModelBuilding: Check for navigation compatibility with keyless type w…

src/EFCore/Metadata/Internal/ForeignKey.cs

@@ -455,18 +455,21 @@ public virtual void UpdatePrincipalToDependentConfigurationSource(ConfigurationS
             EnsureMutable();
 
             var name = propertyIdentity?.Name;
-            if (pointsToPrincipal
-                && PrincipalEntityType.IsKeyless)
+            if (name != null)
             {
-                throw new InvalidOperationException(
-                    CoreStrings.NavigationToKeylessType(name, PrincipalEntityType.DisplayName()));
-            }
+                if (pointsToPrincipal
+                    && PrincipalEntityType.IsKeyless)
+                {
+                    throw new InvalidOperationException(
+                        CoreStrings.NavigationToKeylessType(name, PrincipalEntityType.DisplayName()));
+                }
 
-            if (!pointsToPrincipal
-                && DeclaringEntityType.IsKeyless)
-            {
-                throw new InvalidOperationException(
-                    CoreStrings.NavigationToKeylessType(name, DeclaringEntityType.DisplayName()));
+                if (!pointsToPrincipal
+                    && DeclaringEntityType.IsKeyless)
+                {
+                    throw new InvalidOperationException(
+                        CoreStrings.NavigationToKeylessType(name, DeclaringEntityType.DisplayName()));
+                }
             }
 
             var oldNavigation = pointsToPrincipal ? DependentToPrincipal : PrincipalToDependent;

test/EFCore.Tests/ModelBuilding/OneToManyTestBase.cs

@@ -2683,6 +2683,31 @@ public virtual void Navigation_to_shared_type_is_not_discovered_by_convention()
                     CoreStrings.NonConfiguredNavigationToSharedType("Navigation", nameof(CollectionNavigationToSharedType)),
                     Assert.Throws<InvalidOperationException>(() => modelBuilder.FinalizeModel()).Message);
             }
+
+            [ConditionalFact]
+            public virtual void Reference_navigation_from_keyless_entity_type_works()
+            {
+                var modelBuilder = CreateModelBuilder();
+
+                modelBuilder.Entity<Discount>(entity =>
+                {
+                    entity.HasNoKey();
+
+                    entity.HasOne(d => d.Store).WithMany();
+                });
+
+                var model = modelBuilder.FinalizeModel();
+
+                Assert.Collection(model.GetEntityTypes(),
+                    e =>
+                    {
+                        Assert.Equal(typeof(Discount).DisplayName(), e.Name);
+                        var fk = Assert.Single(e.GetForeignKeys());
+                        Assert.False(fk.IsUnique);
+                        Assert.Equal(nameof(Discount.Store), fk.DependentToPrincipal.Name);
+                    },
+                    e => Assert.Equal(typeof(Store).DisplayName(), e.Name));
+            }
         }
     }
 }

test/EFCore.Tests/ModelBuilding/TestModel.cs

@@ -1162,5 +1162,16 @@ protected class Dre
         protected class DreJr : Dre
         {
         }
+
+        protected class Store
+        {
+            public int StoreId { get; set; }
+        }
+
+        protected class Discount
+        {
+            public int? StoreId { get; set; }
+            public Store? Store { get; set; }
+        }
     }
 }