Avoid dealing with proxies inside the persister

Author: fredericDelaporte

src/NHibernate/Async/Engine/ForeignKeys.cs

@@ -181,15 +181,29 @@ public static async Task<bool> IsNotTransientSlowAsync(string entityName, object
 				return false;
 			}
 
-			if (entity is INHibernateProxy proxy && proxy.HibernateLazyInitializer.IsUninitialized)
+			var proxy = entity as INHibernateProxy;
+			if (proxy?.HibernateLazyInitializer.IsUninitialized == true)
 			{
 				return false;
 			}
 
 			// let the interceptor inspect the instance to decide
+			var interceptorResult = session.Interceptor.IsTransient(entity);
+			if (interceptorResult.HasValue)
+				return interceptorResult;
+
 			// let the persister inspect the instance to decide
-			return session.Interceptor.IsTransient(entity) ??
-			       await (session.GetEntityPersister(entityName, entity).IsTransientAsync(entity, session, cancellationToken)).ConfigureAwait(false);
+			if (proxy != null)
+			{
+				// The persister only deals with unproxied entities.
+				entity = await (proxy.HibernateLazyInitializer.GetImplementationAsync(cancellationToken)).ConfigureAwait(false);
+			}
+
+			await (session
+				.GetEntityPersister(
+					entityName,
+					entity)
+				.IsTransientAsync(entity, session, cancellationToken)).ConfigureAwait(false);
 		}
 
 		/// <summary> 

src/NHibernate/Engine/ForeignKeys.cs

@@ -178,15 +178,29 @@ public static bool IsNotTransientSlow(string entityName, object entity, ISession
 				return false;
 			}
 
-			if (entity is INHibernateProxy proxy && proxy.HibernateLazyInitializer.IsUninitialized)
+			var proxy = entity as INHibernateProxy;
+			if (proxy?.HibernateLazyInitializer.IsUninitialized == true)
 			{
 				return false;
 			}
 
 			// let the interceptor inspect the instance to decide
+			var interceptorResult = session.Interceptor.IsTransient(entity);
+			if (interceptorResult.HasValue)
+				return interceptorResult;
+
 			// let the persister inspect the instance to decide
-			return session.Interceptor.IsTransient(entity) ??
-			       session.GetEntityPersister(entityName, entity).IsTransient(entity, session);
+			if (proxy != null)
+			{
+				// The persister only deals with unproxied entities.
+				entity = proxy.HibernateLazyInitializer.GetImplementation();
+			}
+
+			session
+				.GetEntityPersister(
+					entityName,
+					entity)
+				.IsTransient(entity, session);
 		}
 
 		/// <summary> 

src/NHibernate/Tuple/Entity/AbstractEntityTuplizer.cs

@@ -114,11 +114,6 @@ public object Instantiate(object id)
 
 		public object GetIdentifier(object entity)
 		{
-			if (entity is INHibernateProxy proxy)
-			{
-				return proxy.HibernateLazyInitializer.Identifier;
-			}
-			
 			object id;
 			if (entityMetamodel.IdentifierProperty.IsEmbedded)
 			{