diff --git a/src/EFCore/Extensions/ConventionModelExtensions.cs b/src/EFCore/Extensions/ConventionModelExtensions.cs
index 392115faece..6a2061d3937 100644
--- a/src/EFCore/Extensions/ConventionModelExtensions.cs
+++ b/src/EFCore/Extensions/ConventionModelExtensions.cs
@@ -24,7 +24,7 @@ public static class ConventionModelExtensions
         /// <param name="type"> The type to find the corresponding entity type for. </param>
         /// <returns> The entity type, or <see langword="null" /> if none if found. </returns>
         public static IConventionEntityType FindEntityType([NotNull] this IConventionModel model, [NotNull] Type type)
-            => (IConventionEntityType)((IModel)model).FindEntityType(type);
+            => ((Model)model).FindEntityType(type);
 
         /// <summary>
         ///     Gets the entity type for the given name, defining navigation name
diff --git a/src/EFCore/Extensions/ModelExtensions.cs b/src/EFCore/Extensions/ModelExtensions.cs
index 90386515e27..ecd6bad495c 100644
--- a/src/EFCore/Extensions/ModelExtensions.cs
+++ b/src/EFCore/Extensions/ModelExtensions.cs
@@ -30,7 +30,7 @@ public static class ModelExtensions
         /// <returns> The entity type, or <see langword="null" /> if none if found. </returns>
         [DebuggerStepThrough]
         public static IEntityType FindEntityType([NotNull] this IModel model, [NotNull] Type type)
-            => ((Model)Check.NotNull(model, nameof(model))).FindEntityType(Check.NotNull(type, nameof(type)));
+            => ((Model)model).FindEntityType(Check.NotNull(type, nameof(type)));
 
         /// <summary>
         ///     Gets the entity that maps the given entity class, where the class may be a proxy derived from the
@@ -87,7 +87,7 @@ public static IEntityType FindEntityType(
         /// <returns> The entity types found. </returns>
         [DebuggerStepThrough]
         public static IReadOnlyCollection<IEntityType> GetEntityTypes([NotNull] this IModel model, [NotNull] Type type)
-            => model.AsModel().GetEntityTypes(type);
+            => ((Model)model).GetEntityTypes(type);
 
         /// <summary>
         ///     Gets the entity types matching the given name.
@@ -97,7 +97,7 @@ public static IReadOnlyCollection<IEntityType> GetEntityTypes([NotNull] this IMo
         /// <returns> The entity types found. </returns>
         [DebuggerStepThrough]
         public static IReadOnlyCollection<IEntityType> GetEntityTypes([NotNull] this IModel model, [NotNull] string name)
-            => model.AsModel().GetEntityTypes(name);
+            => ((Model)model).GetEntityTypes(name);
 
         /// <summary>
         ///     Gets a value indicating whether the model contains a corresponding entity type with a defining navigation.
diff --git a/src/EFCore/Extensions/MutableModelExtensions.cs b/src/EFCore/Extensions/MutableModelExtensions.cs
index 51e7383c44e..24371118172 100644
--- a/src/EFCore/Extensions/MutableModelExtensions.cs
+++ b/src/EFCore/Extensions/MutableModelExtensions.cs
@@ -26,7 +26,7 @@ public static class MutableModelExtensions
         /// <param name="type"> The type to find the corresponding entity type for. </param>
         /// <returns> The entity type, or <see langword="null" /> if none if found. </returns>
         public static IMutableEntityType FindEntityType([NotNull] this IMutableModel model, [NotNull] Type type)
-            => (IMutableEntityType)((IModel)model).FindEntityType(type);
+            => ((Model)model).FindEntityType(type);
 
         /// <summary>
         ///     Gets the entity type for the given name, defining navigation name
diff --git a/src/EFCore/Metadata/Conventions/DerivedTypeDiscoveryConvention.cs b/src/EFCore/Metadata/Conventions/DerivedTypeDiscoveryConvention.cs
index 24261c47c78..a7cd632ed2d 100644
--- a/src/EFCore/Metadata/Conventions/DerivedTypeDiscoveryConvention.cs
+++ b/src/EFCore/Metadata/Conventions/DerivedTypeDiscoveryConvention.cs
@@ -38,27 +38,26 @@ public virtual void ProcessEntityTypeAdded(
             if (clrType == null
                 || entityType.HasSharedClrType
                 || entityType.HasDefiningNavigation()
-                || entityType.FindDeclaredOwnership() != null
-                || entityType.Model.FindIsOwnedConfigurationSource(clrType) != null)
+                || entityType.Model.FindIsOwnedConfigurationSource(clrType) != null
+                || entityType.FindOwnership() != null)
             {
                 return;
             }
 
             var model = entityType.Model;
-            var directlyDerivedTypes = model.GetEntityTypes().Where(
-                    t => t != entityType
-                        && t.HasClrType()
-                        && !t.HasDefiningNavigation()
-                        && t.FindDeclaredOwnership() == null
-                        && model.FindIsOwnedConfigurationSource(t.ClrType) == null
-                        && ((t.BaseType == null && clrType.IsAssignableFrom(t.ClrType))
-                            || (t.BaseType == entityType.BaseType && FindClosestBaseType(t) == entityType))
-                        && !t.HasSharedClrType)
-                .ToList();
-
-            foreach (var directlyDerivedType in directlyDerivedTypes)
+            foreach (var directlyDerivedType in model.GetEntityTypes())
             {
-                directlyDerivedType.Builder.HasBaseType(entityType);
+                if (directlyDerivedType != entityType
+                        && directlyDerivedType.HasClrType()
+                        && !directlyDerivedType.HasSharedClrType
+                        && !directlyDerivedType.HasDefiningNavigation()
+                        && model.FindIsOwnedConfigurationSource(directlyDerivedType.ClrType) == null
+                        && directlyDerivedType.FindDeclaredOwnership() == null
+                        && ((directlyDerivedType.BaseType == null && clrType.IsAssignableFrom(directlyDerivedType.ClrType))
+                            || (directlyDerivedType.BaseType == entityType.BaseType && FindClosestBaseType(directlyDerivedType) == entityType)))
+                {
+                    directlyDerivedType.Builder.HasBaseType(entityType);
+                }
             }
         }
     }
diff --git a/src/EFCore/Metadata/Conventions/InheritanceDiscoveryConventionBase.cs b/src/EFCore/Metadata/Conventions/InheritanceDiscoveryConventionBase.cs
index 037edd439ea..bc25a3b36bd 100644
--- a/src/EFCore/Metadata/Conventions/InheritanceDiscoveryConventionBase.cs
+++ b/src/EFCore/Metadata/Conventions/InheritanceDiscoveryConventionBase.cs
@@ -3,7 +3,6 @@
 
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Metadata.Conventions.Infrastructure;
-using Microsoft.EntityFrameworkCore.Utilities;
 
 namespace Microsoft.EntityFrameworkCore.Metadata.Conventions
 {
@@ -33,18 +32,14 @@ protected InheritanceDiscoveryConventionBase([NotNull] ProviderConventionSetBuil
         /// <param name="entityType"> The entity type. </param>
         protected virtual IConventionEntityType FindClosestBaseType([NotNull] IConventionEntityType entityType)
         {
-            Check.NotNull(entityType, nameof(entityType));
-
-            var clrType = entityType.ClrType;
-            Check.NotNull(clrType, nameof(entityType.ClrType));
-
-            var baseType = clrType.BaseType;
+            var baseType = entityType.ClrType.BaseType;
+            var model = entityType.Model;
             IConventionEntityType baseEntityType = null;
-
             while (baseType != null
-                && baseEntityType == null)
+                && baseEntityType == null
+                && baseType != typeof(object))
             {
-                baseEntityType = entityType.Model.FindEntityType(baseType);
+                baseEntityType = model.FindEntityType(baseType);
                 baseType = baseType.BaseType;
             }
 
diff --git a/src/EFCore/Metadata/Internal/EntityType.cs b/src/EFCore/Metadata/Internal/EntityType.cs
index 47ea1f077af..0d43c6489cd 100644
--- a/src/EFCore/Metadata/Internal/EntityType.cs
+++ b/src/EFCore/Metadata/Internal/EntityType.cs
@@ -1151,7 +1151,17 @@ public virtual ForeignKey FindForeignKey(
         ///     doing so can result in application failures when updating to a new Entity Framework Core release.
         /// </summary>
         public virtual ForeignKey FindOwnership()
-            => GetForeignKeys().FirstOrDefault(fk => fk.IsOwnership);
+        {
+            foreach (var foreignKey in GetForeignKeys())
+            {
+                if (foreignKey.IsOwnership)
+                {
+                    return foreignKey;
+                }
+            }
+
+            return null;
+        }
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
@@ -1160,7 +1170,17 @@ public virtual ForeignKey FindOwnership()
         ///     doing so can result in application failures when updating to a new Entity Framework Core release.
         /// </summary>
         public virtual ForeignKey FindDeclaredOwnership()
-            => GetDeclaredForeignKeys().FirstOrDefault(fk => fk.IsOwnership);
+        {
+            foreach (var foreignKey in _foreignKeys)
+            {
+                if (foreignKey.IsOwnership)
+                {
+                    return foreignKey;
+                }
+            }
+
+            return null;
+        }
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
@@ -1180,7 +1200,7 @@ public virtual IEnumerable<ForeignKey> GetDeclaredForeignKeys()
         public virtual IEnumerable<ForeignKey> GetDerivedForeignKeys()
             => _directlyDerivedTypes.Count == 0
                 ? Enumerable.Empty<ForeignKey>()
-                : GetDerivedTypes().SelectMany(et => et.GetDeclaredForeignKeys());
+                : GetDerivedTypes().SelectMany(et => et._foreignKeys);
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
diff --git a/src/EFCore/Metadata/Internal/Model.cs b/src/EFCore/Metadata/Internal/Model.cs
index e5274c68234..dcf73d493cc 100644
--- a/src/EFCore/Metadata/Internal/Model.cs
+++ b/src/EFCore/Metadata/Internal/Model.cs
@@ -285,9 +285,12 @@ public virtual EntityType FindEntityType([NotNull] Type type)
         ///     doing so can result in application failures when updating to a new Entity Framework Core release.
         /// </summary>
         public virtual EntityType FindEntityType([NotNull] string name)
-            => _entityTypes.TryGetValue(Check.NotEmpty(name, nameof(name)), out var entityType)
+        {
+            Check.DebugAssert(!string.IsNullOrEmpty(name), "name is null or empty");
+            return _entityTypes.TryGetValue(name, out var entityType)
                 ? entityType
                 : null;
+        }
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to