Metadata: Fix few Shared Type entity type bugs

- Add DefaultPropertyBagType in shared type by convention
- Throw exception message for nonconfigured navigation pointing to shared type
- Skip Shared type navigation when searching for FKAttribute on property

src/EFCore/Infrastructure/ModelValidator.cs

@@ -196,6 +196,13 @@ protected virtual void ValidatePropertyMapping(
                         continue;
                     }
 
+                    if (model.IsShared(propertyType)
+                        || (targetSequenceType != null && model.IsShared(targetSequenceType)))
+                    {
+                        throw new InvalidOperationException(
+                            CoreStrings.NonconfiguredNavigationToSharedType(actualProperty.Name, entityType.DisplayName()));
+                    }
+
                     var targetType = FindCandidateNavigationPropertyType(actualProperty);
 
                     var isTargetWeakOrOwned

src/EFCore/Metadata/Conventions/ForeignKeyAttributeConvention.cs

@@ -342,7 +342,8 @@ private MemberInfo FindForeignKeyAttributeOnProperty(IConventionEntityType entit
 
                 if (attribute.Name != navigationName
                     || (memberInfo is PropertyInfo propertyInfo
-                        && FindCandidateNavigationPropertyType(propertyInfo) != null))
+                        && (FindCandidateNavigationPropertyType(propertyInfo) != null
+                            || IsNavigationToSharedType(entityType.Model, propertyInfo))))
                 {
                     continue;
                 }
@@ -374,6 +375,11 @@ private MemberInfo FindForeignKeyAttributeOnProperty(IConventionEntityType entit
         private Type FindCandidateNavigationPropertyType([NotNull] PropertyInfo propertyInfo)
             => Dependencies.MemberClassifier.FindCandidateNavigationPropertyType(propertyInfo);
 
+        private bool IsNavigationToSharedType(IConventionModel model, PropertyInfo propertyInfo)
+            => model.IsShared(propertyInfo.PropertyType)
+            || (propertyInfo.PropertyType.TryGetSequenceType() is Type elementType
+                && model.IsShared(elementType));
+
         private static IReadOnlyList<string> FindCandidateDependentPropertiesThroughNavigation(
             IConventionForeignKeyBuilder relationshipBuilder,
             bool pointsToPrincipal)

src/EFCore/Metadata/Conventions/Infrastructure/ProviderConventionSetBuilder.cs

@@ -188,7 +188,7 @@ public virtual ConventionSet CreateConventionSet()
             conventionSet.SkipNavigationInverseChangedConventions.Add(manyToManyJoinEntityTypeConvention);
 
             conventionSet.SkipNavigationForeignKeyChangedConventions.Add(manyToManyJoinEntityTypeConvention);
-            conventionSet.SkipNavigationForeignKeyChangedConventions.Add(keyDiscoveryConvention);            
+            conventionSet.SkipNavigationForeignKeyChangedConventions.Add(keyDiscoveryConvention);
 
             conventionSet.NavigationRemovedConventions.Add(relationshipDiscoveryConvention);
 

src/EFCore/Metadata/Internal/Model.cs

@@ -58,7 +58,8 @@ private readonly SortedDictionary<string, SortedSet<EntityType>> _entityTypesWit
         private readonly Dictionary<string, ConfigurationSource> _ignoredTypeNames
             = new Dictionary<string, ConfigurationSource>(StringComparer.Ordinal);
 
-        private readonly Dictionary<Type, ConfigurationSource> _sharedTypes = new Dictionary<Type, ConfigurationSource>();
+        private readonly Dictionary<Type, ConfigurationSource> _sharedTypes =
+            new Dictionary<Type, ConfigurationSource> { { DefaultPropertyBagType, ConfigurationSource.Convention } };
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to

src/EFCore/Properties/CoreStrings.resx

@@ -1444,4 +1444,7 @@
   <data name="SharedTypeDerivedType" xml:space="preserve">
     <value>The shared type entity type '{entityType}' cannot have a base type.</value>
   </data>
+  <data name="NonconfiguredNavigationToSharedType" xml:space="preserve">
+    <value>The navigation '{navigation}' on '{entityType}' must be configured using Fluent API with an explicit name for the target shared type entity type or excluded by calling 'EntityTypeBuilder.Ignore'.</value>
+  </data>
 </root>

test/EFCore.Specification.Tests/Query/ManyToManyQueryFixtureBase.cs

@@ -147,31 +147,6 @@ public IReadOnlyDictionary<Type, object> GetEntityAsserters()
 
         protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext context)
         {
-            modelBuilder.SharedTypeEntity<Dictionary<string, object>>(
-                "JoinOneToTwoShared",
-                b =>
-                {
-                    b.IndexerProperty<int>("OneId");
-                    b.IndexerProperty<int>("TwoId");
-                });
-
-            modelBuilder.SharedTypeEntity<Dictionary<string, object>>(
-                "JoinOneToThreePayloadFullShared",
-                b =>
-                {
-                    b.IndexerProperty<int>("OneId");
-                    b.IndexerProperty<int>("ThreeId");
-                    b.IndexerProperty<string>("Payload");
-                });
-
-            modelBuilder.SharedTypeEntity<Dictionary<string, object>>(
-                "JoinTwoSelfShared",
-                b =>
-                {
-                    b.IndexerProperty<int>("LeftId");
-                    b.IndexerProperty<int>("RightId");
-                });
-
             modelBuilder.Entity<EntityOne>().Property(e => e.Id).ValueGeneratedNever();
             modelBuilder.Entity<EntityTwo>().Property(e => e.Id).ValueGeneratedNever();
             modelBuilder.Entity<EntityThree>().Property(e => e.Id).ValueGeneratedNever();
@@ -209,24 +184,17 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
                 .HasKey(e => new { e.OneId, e.ThreeId });
 
             // Nav:2 Payload:No Join:Shared Extra:None
-            modelBuilder.Entity<EntityOne>()
-                .HasMany(e => e.TwoSkipShared)
-                .WithMany(e => e.OneSkipShared)
-                .UsingEntity<Dictionary<string, object>>(
-                    "JoinOneToTwoShared",
-                    r => r.HasOne<EntityTwo>().WithMany().HasForeignKey("TwoId"),
-                    l => l.HasOne<EntityOne>().WithMany().HasForeignKey("OneId"))
-                .HasKey("OneId", "TwoId");
+            modelBuilder.Entity<EntityOne>().HasMany(e => e.TwoSkipShared).WithMany(e => e.OneSkipShared);
 
             // Nav:4 Payload:Yes Join:Shared Extra:None
             modelBuilder.Entity<EntityOne>()
                 .HasMany(e => e.ThreeSkipPayloadFullShared)
                 .WithMany(e => e.OneSkipPayloadFullShared)
                 .UsingEntity<Dictionary<string, object>>(
                     "JoinOneToThreePayloadFullShared",
-                    r => r.HasOne<EntityThree>().WithMany(/*"JoinOnePayloadFullShared"*/).HasForeignKey("ThreeId"), // #13729
-                    l => l.HasOne<EntityOne>().WithMany(/*"JoinThreePayloadFullShared"*/).HasForeignKey("OneId")) // #13729
-                .HasKey("OneId", "ThreeId");
+                    r => r.HasOne<EntityThree>().WithMany(e => e.JoinOnePayloadFullShared).HasForeignKey("ThreeId"),
+                    l => l.HasOne<EntityOne>().WithMany(e => e.JoinThreePayloadFullShared).HasForeignKey("OneId"))
+                .IndexerProperty<string>("Payload");
 
             // Nav:6 Payload:Yes Join:Concrete Extra:Self-Ref
             modelBuilder.Entity<EntityOne>()
@@ -272,8 +240,7 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
                 .UsingEntity<Dictionary<string, object>>(
                     "JoinTwoSelfShared",
                     l => l.HasOne<EntityTwo>().WithMany().HasForeignKey("LeftId"),
-                    r => r.HasOne<EntityTwo>().WithMany().OnDelete(DeleteBehavior.NoAction).HasForeignKey("RightId"))
-                .HasKey("LeftId", "RightId");
+                    r => r.HasOne<EntityTwo>().WithMany().HasForeignKey("RightId").OnDelete(DeleteBehavior.NoAction));
 
             // TODO: convert to shared type
             // Nav:2 Payload:No Join:Shared Extra:CompositeKey
@@ -294,15 +261,8 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
                     r => r.HasOne(x => x.Three).WithMany(x => x.JoinCompositeKeyFull))
                 .HasKey(e => new { e.ThreeId, e.CompositeId1, e.CompositeId2, e.CompositeId3 });
 
-            // TODO: convert to shared type
             // Nav:2 Payload:No Join:Shared Extra:Inheritance
-            modelBuilder.Entity<EntityThree>()
-                .HasMany(e => e.RootSkipShared)
-                .WithMany(e => e.ThreeSkipShared)
-                .UsingEntity<JoinThreeToRootShared>(
-                    r => r.HasOne<EntityRoot>().WithMany().HasForeignKey(e => e.RootId),
-                    l => l.HasOne<EntityThree>().WithMany().HasForeignKey(e => e.ThreeId))
-                .HasKey(e => new { e.ThreeId, e.RootId });
+            modelBuilder.Entity<EntityThree>().HasMany(e => e.RootSkipShared).WithMany(e => e.ThreeSkipShared);
 
             // TODO: convert to shared type
             // Nav:2 Payload:No Join:Shared Extra:Inheritance,CompositeKey

test/EFCore.Specification.Tests/TestModels/ManyToManyModel/EntityOne.cs

@@ -25,8 +25,8 @@ public class EntityOne
 
         public virtual ICollection<EntityThree> ThreeSkipPayloadFullShared { get; } = new ObservableCollection<EntityThree>(); // #21684
 
-        // public virtual ICollection<Dictionary<string, object>> JoinThreePayloadFullShared { get; } // #13729
-        //     = new ObservableCollection<Dictionary<string, object>>(); // #21684
+        public virtual ICollection<Dictionary<string, object>> JoinThreePayloadFullShared { get; }
+             = new ObservableCollection<Dictionary<string, object>>(); // #21684
 
         public virtual ICollection<EntityOne> SelfSkipPayloadLeft { get; } = new ObservableCollection<EntityOne>(); // #21684
 

test/EFCore.Specification.Tests/TestModels/ManyToManyModel/EntityThree.cs

@@ -27,8 +27,8 @@ public class EntityThree
 
         public virtual ICollection<EntityOne> OneSkipPayloadFullShared { get; } = new ObservableCollection<EntityOne>(); // #21684
 
-        // public virtual ICollection<Dictionary<string, object>> JoinOnePayloadFullShared { get; } // #13729
-        //     = new ObservableCollection<Dictionary<string, object>>(); // #21684
+        public virtual ICollection<Dictionary<string, object>> JoinOnePayloadFullShared { get; }
+             = new ObservableCollection<Dictionary<string, object>>(); // #21684
 
         public virtual ICollection<EntityCompositeKey> CompositeKeySkipFull { get; }
             = new ObservableCollection<EntityCompositeKey>(); // #21684

test/EFCore.Specification.Tests/TestModels/ManyToManyModel/ImplicitManyToManyA.cs

@@ -0,0 +1,18 @@
+// 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 System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Microsoft.EntityFrameworkCore.TestModels.ManyToManyModel
+{
+    public class ImplicitManyToManyA
+    {
+        [DatabaseGenerated(DatabaseGeneratedOption.None)]
+        public virtual int Id { get; set; }
+        public virtual string Name { get; set; }
+
+        public virtual ICollection<ImplicitManyToManyB> Bs { get; } = new ObservableCollection<ImplicitManyToManyB>();
+    }
+}

test/EFCore.Specification.Tests/TestModels/ManyToManyModel/ImplicitManyToManyB.cs

@@ -0,0 +1,18 @@
+// 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 System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Microsoft.EntityFrameworkCore.TestModels.ManyToManyModel
+{
+    public class ImplicitManyToManyB
+    {
+        [DatabaseGenerated(DatabaseGeneratedOption.None)]
+        public virtual int Id { get; set; }
+        public virtual string Name { get; set; }
+
+        public virtual ICollection<ImplicitManyToManyA> As { get; } = new ObservableCollection<ImplicitManyToManyA>();
+    }
+}