Eliminated double Persister resolution in Loader.InstanceNotYetLoaded flow

src/NHibernate/Async/Loader/Loader.cs

@@ -740,9 +740,7 @@ private async Task InstanceAlreadyLoadedAsync(DbDataReader rs, int i, ILoadable
 				return;
 			}
 
-			var instanceClass = await (GetInstanceClassAsync(rs, i, persister, key.Identifier, session, cancellationToken)).ConfigureAwait(false);
-			entry = entry ?? session.PersistenceContext.GetEntry(obj);
-			await (UpdateLazyPropertiesFromResultSetAsync(rs, i, obj, instanceClass, key, entry, persister, session, cacheBatchingHandler, cancellationToken)).ConfigureAwait(false);
+			await (UpdateLazyPropertiesFromResultSetAsync(rs, i, obj, key, entry, persister, session, cacheBatchingHandler, cancellationToken)).ConfigureAwait(false);
 		}
 
 		/// <summary>
@@ -755,7 +753,7 @@ private async Task<object> InstanceNotYetLoadedAsync(DbDataReader dr, int i, ILo
 			cancellationToken.ThrowIfCancellationRequested();
 			object obj;
 
-			string instanceClass = await (GetInstanceClassAsync(dr, i, persister, key.Identifier, session, cancellationToken)).ConfigureAwait(false);
+			ILoadable concretePersister = await (GetConcretePersisterAsync(dr, i, persister, key.Identifier, session, cancellationToken)).ConfigureAwait(false);
 
 			if (optionalObjectKey != null && key.Equals(optionalObjectKey))
 			{
@@ -764,7 +762,7 @@ private async Task<object> InstanceNotYetLoadedAsync(DbDataReader dr, int i, ILo
 			}
 			else
 			{
-				obj = session.Instantiate(instanceClass, key.Identifier);
+				obj = session.Instantiate(concretePersister, key.Identifier);
 			}
 
 			// need to hydrate it
@@ -773,16 +771,16 @@ private async Task<object> InstanceNotYetLoadedAsync(DbDataReader dr, int i, ILo
 			// (but don't yet initialize the object itself)
 			// note that we acquired LockMode.READ even if it was not requested
 			LockMode acquiredLockMode = lockMode == LockMode.None ? LockMode.Read : lockMode;
-			await (LoadFromResultSetAsync(dr, i, obj, instanceClass, key, acquiredLockMode, persister, session, cancellationToken)).ConfigureAwait(false);
+			await (LoadFromResultSetAsync(dr, i, obj, concretePersister, key, acquiredLockMode, persister, session, cancellationToken)).ConfigureAwait(false);
 
 			// materialize associations (and initialize the object) later
 			hydratedObjects.Add(obj);
 
 			return obj;
 		}
 
-		private async Task UpdateLazyPropertiesFromResultSetAsync(DbDataReader rs, int i, object obj, string instanceClass, EntityKey key,
-		                                               EntityEntry entry, ILoadable rootPersister, ISessionImplementor session,
+		private async Task UpdateLazyPropertiesFromResultSetAsync(DbDataReader rs, int i, object obj, EntityKey key,
+		                                               EntityEntry optionalEntry, ILoadable rootPersister, ISessionImplementor session,
 		                                               Action<IEntityPersister, CachePutData> cacheBatchingHandler, CancellationToken cancellationToken)
 		{
 			cancellationToken.ThrowIfCancellationRequested();
@@ -794,11 +792,8 @@ private async Task UpdateLazyPropertiesFromResultSetAsync(DbDataReader rs, int i
 				return; // No lazy properties were loaded
 			}
 
-			// Get the persister for the _subclass_
-			var persister = instanceClass == rootPersister.EntityName
-				? rootPersister
-				: (ILoadable) Factory.GetEntityPersister(instanceClass);
-
+			var persister = await (GetConcretePersisterAsync(rs, i, rootPersister, key.Identifier, session, cancellationToken)).ConfigureAwait(false);
+			var entry = optionalEntry ?? session.PersistenceContext.GetEntry(obj);
 			// The property values will not be set when the entry status is Loading so in that case we have to get
 			// the uninitialized lazy properties from the loaded state
 			var uninitializedProperties = entry.Status == Status.Loading
@@ -822,7 +817,7 @@ private async Task UpdateLazyPropertiesFromResultSetAsync(DbDataReader rs, int i
 				? EntityAliases[i].SuffixedPropertyAliases
 				: GetSubclassEntityAliases(i, persister);
 
-			if (!await (persister.InitializeLazyPropertiesAsync(rs, id, obj, rootPersister, cols, updateLazyProperties, fetchAllProperties, session, cancellationToken)).ConfigureAwait(false))
+			if (!await (persister.InitializeLazyPropertiesAsync(rs, id, obj, cols, updateLazyProperties, fetchAllProperties, session, cancellationToken)).ConfigureAwait(false))
 			{
 				return;
 			}
@@ -882,18 +877,13 @@ internal static async Task UpdateCacheForEntityAsync(
 		/// an array of "hydrated" values (do not resolve associations yet),
 		/// and pass the hydrated state to the session.
 		/// </summary>
-		private async Task LoadFromResultSetAsync(DbDataReader rs, int i, object obj, string instanceClass, EntityKey key,
+		private async Task LoadFromResultSetAsync(DbDataReader rs, int i, object obj, ILoadable persister, EntityKey key,
 									   LockMode lockMode, ILoadable rootPersister,
 									   ISessionImplementor session, CancellationToken cancellationToken)
 		{
 			cancellationToken.ThrowIfCancellationRequested();
 			object id = key.Identifier;
 
-			// Get the persister for the _subclass_
-			ILoadable persister = instanceClass == rootPersister.EntityName
-				? rootPersister
-				: (ILoadable) Factory.GetEntityPersister(instanceClass);
-
 			if (Log.IsDebugEnabled())
 			{
 				Log.Debug("Initializing object from DataReader: {0}", MessageHelper.InfoString(persister, id));
@@ -921,7 +911,7 @@ private async Task LoadFromResultSetAsync(DbDataReader rs, int i, object obj, st
 		/// <summary>
 		/// Determine the concrete class of an instance for the <c>DbDataReader</c>
 		/// </summary>
-		private async Task<string> GetInstanceClassAsync(DbDataReader rs, int i, ILoadable persister, object id, ISessionImplementor session, CancellationToken cancellationToken)
+		private async Task<ILoadable> GetConcretePersisterAsync(DbDataReader rs, int i, ILoadable persister, object id, ISessionImplementor session, CancellationToken cancellationToken)
 		{
 			cancellationToken.ThrowIfCancellationRequested();
 			if (persister.HasSubclasses)
@@ -939,9 +929,11 @@ private async Task<string> GetInstanceClassAsync(DbDataReader rs, int i, ILoadab
 												  persister.EntityName);
 				}
 
-				return result;
+				return persister.EntityName == result
+					? persister
+					: (ILoadable) Factory.GetEntityPersister(result);
 			}
-			return persister.EntityName;
+			return persister;
 		}
 
 		/// <summary>

src/NHibernate/Async/Persister/Entity/AbstractEntityPersister.cs

@@ -62,7 +62,7 @@ public virtual Task BindValuesAsync(DbCommand ps, CancellationToken cancellation
 		}
 
 		public Task InitializeLazyPropertiesAsync(
-			DbDataReader rs, object id, object entity, ILoadable rootPersister, string[][] suffixedPropertyColumns,
+			DbDataReader rs, object id, object entity, string[][] suffixedPropertyColumns,
 			string[] uninitializedLazyProperties, bool allLazyProperties, ISessionImplementor session, CancellationToken cancellationToken)
 		{
 			if (!HasLazyProperties)

src/NHibernate/Async/Persister/Entity/ILoadable.cs

@@ -73,7 +73,7 @@ public static Task<object[]> HydrateAsync(
 		/// </summary>
 		//6.0 TODO: Change to void and merge into ILoadable
 		internal static async Task<bool> InitializeLazyPropertiesAsync(
-			this ILoadable loadable, DbDataReader rs, object id, object entity, ILoadable rootPersister, string[][] suffixedPropertyColumns,
+			this ILoadable loadable, DbDataReader rs, object id, object entity, string[][] suffixedPropertyColumns,
 			string[] uninitializedLazyProperties, bool allLazyProperties, ISessionImplementor session, CancellationToken cancellationToken)
 		{
 			cancellationToken.ThrowIfCancellationRequested();
@@ -83,7 +83,6 @@ internal static async Task<bool> InitializeLazyPropertiesAsync(
 					rs,
 					id,
 					entity,
-					rootPersister,
 					suffixedPropertyColumns,
 					uninitializedLazyProperties,
 					allLazyProperties,

src/NHibernate/Engine/ISessionImplementor.cs

@@ -21,6 +21,16 @@ namespace NHibernate.Engine
 	// 6.0 TODO: Convert to interface methods, excepted SwitchCacheMode
 	internal static partial class SessionImplementorExtensions
 	{
+		/// <summary>
+		/// Instantiate the entity class, initializing with the given identifier
+		/// </summary>
+		internal static object Instantiate(this ISessionImplementor session, IEntityPersister persister, object id)
+		{
+			if(session is AbstractSessionImpl impl)
+				return impl.Instantiate(persister, id);
+			return session.Instantiate(persister.EntityName, id);
+		}
+
 		internal static IDisposable BeginContext(this ISessionImplementor session)
 		{
 			if (session == null)
@@ -249,6 +259,8 @@ public partial interface ISessionImplementor
 		/// </summary>
 		object GetContextEntityIdentifier(object obj);
 
+		//Since 5.3
+		//TODO 6.0 Remove (see SessionImplementorExtensions.Instantiate for replacement)
 		/// <summary>
 		/// Instantiate the entity class, initializing with the given identifier
 		/// </summary>

src/NHibernate/Event/IEventSource.cs

@@ -16,6 +16,7 @@ public partial interface IEventSource : ISessionImplementor, ISession
 		/// </summary>
 		bool AutoFlushSuspended { get; }
 
+		//6.0 TODO Remove it (it's added directly to ISessionImplementor)
 		/// <summary> 
 		/// Instantiate an entity instance, using either an interceptor,
 		/// or the given persister

src/NHibernate/Impl/AbstractSessionImpl.cs

@@ -192,8 +192,19 @@ public IList ListFilter(object collection, IQueryExpression queryExpression, Que
 		public abstract void FlushBeforeTransactionCompletion();
 		public abstract void AfterTransactionCompletion(bool successful, ITransaction tx);
 		public abstract object GetContextEntityIdentifier(object obj);
+
+		//Since 5.3
+		[Obsolete("Use override with persister parameter")]
 		public abstract object Instantiate(string clazz, object id);
 
+		//6.0 TODO: Make abstract
+		public virtual object Instantiate(IEntityPersister persister, object id)
+		{
+#pragma warning disable 618
+			return Instantiate(persister.EntityName, id);
+#pragma warning restore 618
+		}
+
 		public virtual IList List(NativeSQLQuerySpecification spec, QueryParameters queryParameters)
 		{
 			using (BeginProcess())

src/NHibernate/Impl/SessionImpl.cs

@@ -761,6 +761,8 @@ private IQueryExpressionPlan GetFilterQueryPlan(string role, bool shallow, strin
 				: Factory.QueryPlanCache.GetFilterQueryPlan(filter, role, shallow, EnabledFilters);
 		}
 
+		//Since 5.3
+		[Obsolete("Use override with persister parameter")]
 		public override object Instantiate(string clazz, object id)
 		{
 			using (BeginProcess())
@@ -785,7 +787,7 @@ public ActionQueue ActionQueue
 		/// <param name="persister"></param>
 		/// <param name="id"></param>
 		/// <returns></returns>
-		public object Instantiate(IEntityPersister persister, object id)
+		public override object Instantiate(IEntityPersister persister, object id)
 		{
 			using (BeginProcess())
 			{

src/NHibernate/Impl/StatelessSessionImpl.cs

@@ -244,11 +244,18 @@ public override object GetContextEntityIdentifier(object obj)
 			}
 		}
 
+		//Since 5.3
+		[Obsolete("Use override with persister parameter")]
 		public override object Instantiate(string clazz, object id)
+		{
+		  return Instantiate(Factory.GetEntityPersister(clazz), id);
+		}
+
+		public override object Instantiate(IEntityPersister persister, object id)
 		{
 			using (BeginProcess())
 			{
-				return Factory.GetEntityPersister(clazz).Instantiate(id);
+				return persister.Instantiate(id);
 			}
 		}
 

src/NHibernate/Loader/Loader.cs

@@ -1070,9 +1070,7 @@ private void InstanceAlreadyLoaded(DbDataReader rs, int i, ILoadable persister,
 				return;
 			}
 
-			var instanceClass = GetInstanceClass(rs, i, persister, key.Identifier, session);
-			entry = entry ?? session.PersistenceContext.GetEntry(obj);
-			UpdateLazyPropertiesFromResultSet(rs, i, obj, instanceClass, key, entry, persister, session, cacheBatchingHandler);
+			UpdateLazyPropertiesFromResultSet(rs, i, obj, key, entry, persister, session, cacheBatchingHandler);
 		}
 
 		private void CacheByUniqueKey(int i, IEntityPersister persister, object obj, ISessionImplementor session, bool alreadyLoaded)
@@ -1116,7 +1114,7 @@ private object InstanceNotYetLoaded(DbDataReader dr, int i, ILoadable persister,
 		{
 			object obj;
 
-			string instanceClass = GetInstanceClass(dr, i, persister, key.Identifier, session);
+			ILoadable concretePersister = GetConcretePersister(dr, i, persister, key.Identifier, session);
 
 			if (optionalObjectKey != null && key.Equals(optionalObjectKey))
 			{
@@ -1125,7 +1123,7 @@ private object InstanceNotYetLoaded(DbDataReader dr, int i, ILoadable persister,
 			}
 			else
 			{
-				obj = session.Instantiate(instanceClass, key.Identifier);
+				obj = session.Instantiate(concretePersister, key.Identifier);
 			}
 
 			// need to hydrate it
@@ -1134,7 +1132,7 @@ private object InstanceNotYetLoaded(DbDataReader dr, int i, ILoadable persister,
 			// (but don't yet initialize the object itself)
 			// note that we acquired LockMode.READ even if it was not requested
 			LockMode acquiredLockMode = lockMode == LockMode.None ? LockMode.Read : lockMode;
-			LoadFromResultSet(dr, i, obj, instanceClass, key, acquiredLockMode, persister, session);
+			LoadFromResultSet(dr, i, obj, concretePersister, key, acquiredLockMode, persister, session);
 
 			// materialize associations (and initialize the object) later
 			hydratedObjects.Add(obj);
@@ -1159,8 +1157,8 @@ private HashSet<string> GetFetchLazyProperties(int i)
 			return array?[i];
 		}
 
-		private void UpdateLazyPropertiesFromResultSet(DbDataReader rs, int i, object obj, string instanceClass, EntityKey key,
-		                                               EntityEntry entry, ILoadable rootPersister, ISessionImplementor session,
+		private void UpdateLazyPropertiesFromResultSet(DbDataReader rs, int i, object obj, EntityKey key,
+		                                               EntityEntry optionalEntry, ILoadable rootPersister, ISessionImplementor session,
 		                                               Action<IEntityPersister, CachePutData> cacheBatchingHandler)
 		{
 			var fetchAllProperties = IsEagerPropertyFetchEnabled(i);
@@ -1171,11 +1169,8 @@ private void UpdateLazyPropertiesFromResultSet(DbDataReader rs, int i, object ob
 				return; // No lazy properties were loaded
 			}
 
-			// Get the persister for the _subclass_
-			var persister = instanceClass == rootPersister.EntityName
-				? rootPersister
-				: (ILoadable) Factory.GetEntityPersister(instanceClass);
-
+			var persister = GetConcretePersister(rs, i, rootPersister, key.Identifier, session);
+			var entry = optionalEntry ?? session.PersistenceContext.GetEntry(obj);
 			// The property values will not be set when the entry status is Loading so in that case we have to get
 			// the uninitialized lazy properties from the loaded state
 			var uninitializedProperties = entry.Status == Status.Loading
@@ -1199,7 +1194,7 @@ private void UpdateLazyPropertiesFromResultSet(DbDataReader rs, int i, object ob
 				? EntityAliases[i].SuffixedPropertyAliases
 				: GetSubclassEntityAliases(i, persister);
 
-			if (!persister.InitializeLazyProperties(rs, id, obj, rootPersister, cols, updateLazyProperties, fetchAllProperties, session))
+			if (!persister.InitializeLazyProperties(rs, id, obj, cols, updateLazyProperties, fetchAllProperties, session))
 			{
 				return;
 			}
@@ -1258,17 +1253,12 @@ internal static void UpdateCacheForEntity(
 		/// an array of "hydrated" values (do not resolve associations yet),
 		/// and pass the hydrated state to the session.
 		/// </summary>
-		private void LoadFromResultSet(DbDataReader rs, int i, object obj, string instanceClass, EntityKey key,
+		private void LoadFromResultSet(DbDataReader rs, int i, object obj, ILoadable persister, EntityKey key,
 									   LockMode lockMode, ILoadable rootPersister,
 									   ISessionImplementor session)
 		{
 			object id = key.Identifier;
 
-			// Get the persister for the _subclass_
-			ILoadable persister = instanceClass == rootPersister.EntityName
-				? rootPersister
-				: (ILoadable) Factory.GetEntityPersister(instanceClass);
-
 			if (Log.IsDebugEnabled())
 			{
 				Log.Debug("Initializing object from DataReader: {0}", MessageHelper.InfoString(persister, id));
@@ -1304,7 +1294,7 @@ private string[][] GetSubclassEntityAliases(int i, ILoadable persister)
 		/// <summary>
 		/// Determine the concrete class of an instance for the <c>DbDataReader</c>
 		/// </summary>
-		private string GetInstanceClass(DbDataReader rs, int i, ILoadable persister, object id, ISessionImplementor session)
+		private ILoadable GetConcretePersister(DbDataReader rs, int i, ILoadable persister, object id, ISessionImplementor session)
 		{
 			if (persister.HasSubclasses)
 			{
@@ -1321,9 +1311,11 @@ private string GetInstanceClass(DbDataReader rs, int i, ILoadable persister, obj
 												  persister.EntityName);
 				}
 
-				return result;
+				return persister.EntityName == result
+					? persister
+					: (ILoadable) Factory.GetEntityPersister(result);
 			}
-			return persister.EntityName;
+			return persister;
 		}
 
 		/// <summary>

src/NHibernate/Persister/Entity/AbstractEntityPersister.cs

@@ -1395,7 +1395,7 @@ public virtual object InitializeLazyProperty(string fieldName, object entity, IS
 		}
 
 		public void InitializeLazyProperties(
-			DbDataReader rs, object id, object entity, ILoadable rootPersister, string[][] suffixedPropertyColumns,
+			DbDataReader rs, object id, object entity, string[][] suffixedPropertyColumns,
 			string[] uninitializedLazyProperties, bool allLazyProperties, ISessionImplementor session)
 		{
 			if (!HasLazyProperties)

src/NHibernate/Persister/Entity/ILoadable.cs

@@ -107,7 +107,7 @@ public static object[] Hydrate(
 		/// </summary>
 		//6.0 TODO: Change to void and merge into ILoadable
 		internal static bool InitializeLazyProperties(
-			this ILoadable loadable, DbDataReader rs, object id, object entity, ILoadable rootPersister, string[][] suffixedPropertyColumns,
+			this ILoadable loadable, DbDataReader rs, object id, object entity, string[][] suffixedPropertyColumns,
 			string[] uninitializedLazyProperties, bool allLazyProperties, ISessionImplementor session)
 		{
 			if (loadable is AbstractEntityPersister abstractEntityPersister)
@@ -116,7 +116,6 @@ internal static bool InitializeLazyProperties(
 					rs,
 					id,
 					entity,
-					rootPersister,
 					suffixedPropertyColumns,
 					uninitializedLazyProperties,
 					allLazyProperties,