Join-fetching with property-ref results in select n+1

src/NHibernate.Test/Async/NHSpecificTest/GH1226/Fixture.cs

@@ -0,0 +1,95 @@
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by AsyncGenerator.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH1226
+{
+	using System.Threading.Tasks;
+	[TestFixture]
+	public class FixtureAsync : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+			base.OnSetUp();
+
+			using (var session = OpenSession())
+			{
+				using (var tx = session.BeginTransaction())
+				{
+					var bank = new Bank { Code = "01234" };
+					session.Save(bank);
+
+					var account = new Account { Bank = bank };
+					session.Save(account);
+
+					var account2 = new Account { Bank = bank };
+					session.Save(account2);
+
+					tx.Commit();
+				}
+			}
+		}
+
+		[Test]
+		public async Task BankShouldBeJoinFetchedAsync()
+		{
+			using (var session = OpenSession())
+			{
+				var wasStatisticsEnabled = session.SessionFactory.Statistics.IsStatisticsEnabled;
+				session.SessionFactory.Statistics.IsStatisticsEnabled = true;
+
+				long statementCount;
+
+				using (var tx = session.BeginTransaction())
+				{
+					// Bug only occurs if the Banks are already in the session cache.
+					var preloadedBanks = await (session.CreateQuery("from Bank").ListAsync<Bank>());
+
+					var countBeforeQuery = session.SessionFactory.Statistics.PrepareStatementCount;
+
+					Console.WriteLine("Query: -------------------------------------------------------");
+
+					var accounts = await (session.CreateQuery("from Account a left join fetch a.Bank").ListAsync<Account>());
+					IList<Bank> associatedBanks = accounts.Select(x => x.Bank).ToList();
+
+					var countAfterQuery = session.SessionFactory.Statistics.PrepareStatementCount;
+					statementCount = countAfterQuery - countBeforeQuery;
+
+					Console.WriteLine("End ----------------------------------------------------------");
+
+					await (tx.CommitAsync());
+				}
+
+				session.SessionFactory.Statistics.IsStatisticsEnabled = wasStatisticsEnabled;
+
+				Assert.That(statementCount, Is.EqualTo(1));
+			}
+		}
+
+		protected override void OnTearDown()
+		{
+			base.OnTearDown();
+
+			using (var session = OpenSession())
+			{
+				using (var tx = session.BeginTransaction())
+				{
+					session.Delete("from Account");
+					session.Delete("from Bank");
+					tx.Commit();
+				}
+			}
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH1226/Fixture.cs

@@ -0,0 +1,84 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH1226
+{
+	[TestFixture]
+	public class Fixture : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+			base.OnSetUp();
+
+			using (var session = OpenSession())
+			{
+				using (var tx = session.BeginTransaction())
+				{
+					var bank = new Bank { Code = "01234" };
+					session.Save(bank);
+
+					var account = new Account { Bank = bank };
+					session.Save(account);
+
+					var account2 = new Account { Bank = bank };
+					session.Save(account2);
+
+					tx.Commit();
+				}
+			}
+		}
+
+		[Test]
+		public void BankShouldBeJoinFetched()
+		{
+			using (var session = OpenSession())
+			{
+				var wasStatisticsEnabled = session.SessionFactory.Statistics.IsStatisticsEnabled;
+				session.SessionFactory.Statistics.IsStatisticsEnabled = true;
+
+				long statementCount;
+
+				using (var tx = session.BeginTransaction())
+				{
+					// Bug only occurs if the Banks are already in the session cache.
+					var preloadedBanks = session.CreateQuery("from Bank").List<Bank>();
+
+					var countBeforeQuery = session.SessionFactory.Statistics.PrepareStatementCount;
+
+					Console.WriteLine("Query: -------------------------------------------------------");
+
+					var accounts = session.CreateQuery("from Account a left join fetch a.Bank").List<Account>();
+					IList<Bank> associatedBanks = accounts.Select(x => x.Bank).ToList();
+
+					var countAfterQuery = session.SessionFactory.Statistics.PrepareStatementCount;
+					statementCount = countAfterQuery - countBeforeQuery;
+
+					Console.WriteLine("End ----------------------------------------------------------");
+
+					tx.Commit();
+				}
+
+				session.SessionFactory.Statistics.IsStatisticsEnabled = wasStatisticsEnabled;
+
+				Assert.That(statementCount, Is.EqualTo(1));
+			}
+		}
+
+		protected override void OnTearDown()
+		{
+			base.OnTearDown();
+
+			using (var session = OpenSession())
+			{
+				using (var tx = session.BeginTransaction())
+				{
+					session.Delete("from Account");
+					session.Delete("from Bank");
+					tx.Commit();
+				}
+			}
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH1226/Mappings.hbm.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
+                   assembly="NHibernate.Test"
+                   namespace="NHibernate.Test.NHSpecificTest.GH1226">
+  <class name="Account">
+    <id name="Id">
+      <generator class="guid"/>
+    </id>
+    <many-to-one fetch="join" name="Bank" property-ref="Code"/>
+  </class>
+
+  <class name="Bank">
+    <id name="Id">
+      <generator class="guid"/>
+    </id>
+    <property name="Code" unique="true"/>
+  </class>
+</hibernate-mapping>

src/NHibernate.Test/NHSpecificTest/GH1226/Model.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace NHibernate.Test.NHSpecificTest.GH1226
+{
+	public class Account
+	{
+		public virtual Guid Id { get; set; }
+		public virtual Bank Bank { get; set; }
+	}
+
+	public class Bank
+	{
+		public virtual Guid Id { get; set; }
+		public virtual string Code { get; set; }
+	}
+}

src/NHibernate/Async/Loader/Loader.cs

@@ -650,6 +650,8 @@ private async Task InstanceAlreadyLoadedAsync(DbDataReader rs, int i, IEntityPer
 					entry.LockMode = lockMode;
 				}
 			}
+
+			CacheByUniqueKey(i, persister, obj, session);
 		}
 
 		/// <summary>

src/NHibernate/Loader/Loader.cs

@@ -972,6 +972,34 @@ private void InstanceAlreadyLoaded(DbDataReader rs, int i, IEntityPersister pers
 					entry.LockMode = lockMode;
 				}
 			}
+
+			CacheByUniqueKey(i, persister, obj, session);
+		}
+
+		private void CacheByUniqueKey(int i, IEntityPersister persister, object obj, ISessionImplementor session)
+		{
+			// #1226: If it is already loaded and can be loaded from an association with a property ref, make
+			// sure it is also cached by its unique key.
+			var ukName = OwnerAssociationTypes?[i]?.RHSUniqueKeyPropertyName;
+			if (ukName == null)
+				return;
+			var index = ((IUniqueKeyLoadable)persister).GetPropertyIndex(ukName);
+			var ukValue = persister.GetPropertyValue(obj, index);
+			// ukValue can be null for two reasons:
+			//  - Entity currently loading and not yet fully hydrated. In such case, it has already been handled by
+			//    InstanceNotYetLoaded on a previous row, there is nothing more to do. This case could also be
+			//    detected with "session.PersistenceContext.GetEntry(obj).Status == Status.Loading", but since there
+			//    is a second case, just test for ukValue null.
+			//  - Entity association is unset in session but not yet persisted, autoflush disabled: ignore. We are
+			//    already in an error case: querying entities changed in session without flushing them before querying.
+			//    So here it gets loaded as if it were still associated, but we do not have the key anymore in session:
+			//    we cannot cache it, so long for the additionnal round-trip this will cause. (Do not fallback on
+			//    reading the key in rs, this is stale data in regard to the session state.)
+			if (ukValue == null)
+				return;
+			var type = persister.PropertyTypes[index];
+			var euk = new EntityUniqueKey(persister.EntityName, ukName, ukValue, type, session.Factory);
+			session.PersistenceContext.AddEntity(euk, obj);
 		}
 
 		/// <summary>