Fix missing join for reused fetch join not used in Select

src/NHibernate.Test/Async/NHSpecificTest/GH3263/ReuseFetchJoinFixture.cs

@@ -0,0 +1,99 @@
+//------------------------------------------------------------------------------
+// <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.Linq;
+using NHibernate.Linq;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH3263
+{
+	using System.Threading.Tasks;
+	[TestFixture]
+	public class ReuseFetchJoinFixtureAsync : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+			using var s = OpenSession();
+			using var t = s.BeginTransaction();
+			var em = new Employee() { Name = "x", OptionalInfo = new OptionalInfo() };
+			em.OptionalInfo.Employee = em;
+			s.Save(em);
+			t.Commit();
+		}
+		protected override void OnTearDown()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+			session.CreateQuery("delete from System.Object").ExecuteUpdate();
+
+			transaction.Commit();
+		}
+
+		[Test]
+		public async Task ReuseJoinScalarSelectAsync()
+		{
+			using var session = OpenSession();
+			await (session.Query<Employee>()
+				.Fetch(x => x.OptionalInfo)
+				.Where(x => x.OptionalInfo != null)
+				.Select(x => new { x.OptionalInfo.Age })
+				.ToListAsync());
+		}
+
+		[Test]
+		public async Task ReuseJoinScalarSelectHqlAsync()
+		{
+			using var session = OpenSession();
+			await (session.CreateQuery(
+				"select x.OptionalInfo.Age " +
+				"from Employee x " +
+				"fetch x.OptionalInfo " +
+				"where x.OptionalInfo != null ").ListAsync());
+
+		}
+
+		[Test]
+		public async Task ReuseJoinScalarSelectHql2Async()
+		{
+			using var session = OpenSession();
+			await (session.CreateQuery(
+				"select x.OptionalInfo.Age " +
+				"from Employee x " +
+				"join fetch x.OptionalInfo o " +
+				"where o != null ").ListAsync());
+		}
+
+		[Test]
+		public async Task ReuseJoinScalarSelectHql3Async()
+		{
+			using var session = OpenSession();
+			await (session.CreateQuery(
+				"select x.OptionalInfo.Age from Employee x " +
+				"join fetch x.OptionalInfo " +
+				"where x.OptionalInfo != null ").ListAsync());
+		}
+
+		[Test]
+		public async Task ReuseJoinEntityAndScalarSelectAsync()
+		{
+			using var session = OpenSession();
+			using var sqlLog = new SqlLogSpy();
+
+			var x = await (session.Query<Employee>()
+				.Fetch(x => x.OptionalInfo)
+				.Where(x => x.OptionalInfo != null)
+				.Select(x => new { x, x.OptionalInfo.Age })
+				.FirstAsync());
+
+			Assert.That(sqlLog.Appender.GetEvents().Length, Is.EqualTo(1));
+			Assert.That(NHibernateUtil.IsInitialized(x.x.OptionalInfo), Is.True);
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH3263/Entity.cs

@@ -0,0 +1,16 @@
+namespace NHibernate.Test.NHSpecificTest.GH3263
+{
+	public class Employee
+	{
+		public virtual int EmployeeId { get; set; }
+		public virtual string Name { get; set; }
+		public virtual OptionalInfo OptionalInfo { get; set; }
+	}
+
+	public class OptionalInfo
+	{
+		public virtual int EmployeeId { get; set; }
+		public virtual int Age { get; set; }
+		public virtual Employee Employee { get; set; }
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH3263/Mappings.hbm.xml

@@ -0,0 +1,25 @@
+<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"  assembly="NHibernate.Test"
+                   namespace="NHibernate.Test.NHSpecificTest.GH3263">
+  <class name="Employee" table="Employee">
+    <id name="EmployeeId">
+      <column name="EmployeeId" />
+      <generator class="identity" />
+    </id>
+    <property name="Name" >
+      <column name="Name" not-null="true" />
+    </property>
+    <one-to-one cascade="save-update" name="OptionalInfo" foreign-key="none"/>
+  </class>
+  <class name="OptionalInfo" table="OptionalInfo">
+    <id name="EmployeeId" >
+      <column name="EmployeeId" />
+      <generator class="foreign">
+        <param name="property">Employee</param>
+      </generator>
+    </id>
+    <property name="Age">
+      <column name="Age" not-null="true" />
+    </property>
+    <one-to-one cascade="none" name="Employee" foreign-key="none" />
+  </class>
+</hibernate-mapping>

src/NHibernate.Test/NHSpecificTest/GH3263/ReuseFetchJoinFixture.cs

@@ -0,0 +1,88 @@
+using System.Linq;
+using NHibernate.Linq;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH3263
+{
+	[TestFixture]
+	public class ReuseFetchJoinFixture : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+			using var s = OpenSession();
+			using var t = s.BeginTransaction();
+			var em = new Employee() { Name = "x", OptionalInfo = new OptionalInfo() };
+			em.OptionalInfo.Employee = em;
+			s.Save(em);
+			t.Commit();
+		}
+		protected override void OnTearDown()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+			session.CreateQuery("delete from System.Object").ExecuteUpdate();
+
+			transaction.Commit();
+		}
+
+		[Test]
+		public void ReuseJoinScalarSelect()
+		{
+			using var session = OpenSession();
+			session.Query<Employee>()
+				.Fetch(x => x.OptionalInfo)
+				.Where(x => x.OptionalInfo != null)
+				.Select(x => new { x.OptionalInfo.Age })
+				.ToList();
+		}
+
+		[Test]
+		public void ReuseJoinScalarSelectHql()
+		{
+			using var session = OpenSession();
+			session.CreateQuery(
+				"select x.OptionalInfo.Age " +
+				"from Employee x " +
+				"fetch x.OptionalInfo " +
+				"where x.OptionalInfo != null ").List();
+
+		}
+
+		[Test]
+		public void ReuseJoinScalarSelectHql2()
+		{
+			using var session = OpenSession();
+			session.CreateQuery(
+				"select x.OptionalInfo.Age " +
+				"from Employee x " +
+				"join fetch x.OptionalInfo o " +
+				"where o != null ").List();
+		}
+
+		[Test]
+		public void ReuseJoinScalarSelectHql3()
+		{
+			using var session = OpenSession();
+			session.CreateQuery(
+				"select x.OptionalInfo.Age from Employee x " +
+				"join fetch x.OptionalInfo " +
+				"where x.OptionalInfo != null ").List();
+		}
+
+		[Test]
+		public void ReuseJoinEntityAndScalarSelect()
+		{
+			using var session = OpenSession();
+			using var sqlLog = new SqlLogSpy();
+
+			var x = session.Query<Employee>()
+				.Fetch(x => x.OptionalInfo)
+				.Where(x => x.OptionalInfo != null)
+				.Select(x => new { x, x.OptionalInfo.Age })
+				.First();
+
+			Assert.That(sqlLog.Appender.GetEvents().Length, Is.EqualTo(1));
+			Assert.That(NHibernateUtil.IsInitialized(x.x.OptionalInfo), Is.True);
+		}
+	}
+}

src/NHibernate/Hql/Ast/ANTLR/Tree/DotNode.cs

@@ -558,6 +558,8 @@ private void DereferenceEntityJoin(string classAlias, EntityType propertyType, b
 				{
 					elem.JoinSequence.SetJoinType(_joinType);
 				}
+
+				elem.ReusedJoin = true;
 				currentFromClause.AddDuplicateAlias(classAlias, elem);
 			}
 

src/NHibernate/Hql/Ast/ANTLR/Tree/FromElement.cs

@@ -631,6 +631,7 @@ internal virtual string[] GetIdentityColumns(string alias)
 		}
 
 		internal bool UseTableAliases => Walker.StatementType == HqlSqlWalker.SELECT || Walker.IsSubQuery;
+		internal bool ReusedJoin { get; set; }
 
 		public void HandlePropertyBeingDereferenced(IType propertySource, string propertyName)
 		{

src/NHibernate/Hql/Ast/ANTLR/Tree/SelectClause.cs

@@ -245,7 +245,7 @@ private List<FromElement> GetFetchedFromElements(FromClause fromClause)
 					// throw new QueryException(string.Format(JoinFetchWithoutOwnerExceptionMsg, fromElement.GetDisplayText()));
 
 					//throw away the fromElement. It's clearly redundant.
-					if (fromElement.FromClause == fromClause)
+					if (fromElement.FromClause == fromClause && !fromElement.ReusedJoin)
 					{
 						fromElement.Parent.RemoveChild(fromElement);
 					}