Use entities prepared by Loader in hql select projections

src/NHibernate.Test/Async/NHSpecificTest/GH2064/OneToOneSelectProjectionFixture.cs

@@ -0,0 +1,118 @@
+//------------------------------------------------------------------------------
+// <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.Cfg.MappingSchema;
+using NHibernate.Mapping.ByCode;
+using NUnit.Framework;
+using NHibernate.Linq;
+
+namespace NHibernate.Test.NHSpecificTest.GH2064
+{
+	using System.Threading.Tasks;
+	[TestFixture]
+	public class OneToOneSelectProjectionFixtureAsync : TestCaseMappingByCode
+	{
+		protected override HbmMapping GetMappings()
+		{
+			var mapper = new ModelMapper();
+			mapper.Class<OneToOneEntity>(
+				rc =>
+				{
+					rc.Id(e => e.Id, m => m.Generator(Generators.Assigned));
+					rc.Property(e => e.Name);
+				});
+
+			mapper.Class<ParentEntity>(
+				rc =>
+				{
+					rc.Id(e => e.Id, m => m.Generator(Generators.GuidComb));
+					rc.Property(e => e.Name);
+					rc.OneToOne(e => e.OneToOne, m => { });
+				});
+
+			return mapper.CompileMappingForAllExplicitlyAddedEntities();
+		}
+
+		protected override void OnSetUp()
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				var nullableOwner = new ParentEntity() {Name = "Owner",};
+				var oneToOne = new OneToOneEntity() {Name = "OneToOne"};
+				nullableOwner.OneToOne = oneToOne;
+				session.Save(nullableOwner);
+				oneToOne.Id = nullableOwner.Id;
+				session.Save(oneToOne);
+				session.Flush();
+
+				transaction.Commit();
+			}
+		}
+
+		protected override void OnTearDown()
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				// The HQL delete does all the job inside the database without loading the entities, but it does
+				// not handle delete order for avoiding violating constraints if any. Use
+				// session.Delete("from System.Object");
+				// instead if in need of having NHibernate ordering the deletes, but this will cause
+				// loading the entities in the session.
+				session.CreateQuery("delete from System.Object").ExecuteUpdate();
+
+				transaction.Commit();
+			}
+		}
+
+		[Test]
+		public async Task QueryOneToOneAsync()
+		{
+			using (var session = OpenSession())
+			{
+				var entity =
+					await (session
+						.Query<ParentEntity>()
+						.FirstOrDefaultAsync());
+				Assert.That(entity.OneToOne, Is.Not.Null);
+			}
+		}
+
+		[Test]
+		public async Task QueryOneToOneProjectionAsync()
+		{
+			using (var session = OpenSession())
+			{
+				var entity =
+					await (session
+						.Query<ParentEntity>()
+						.Select(
+							x => new
+							{
+								x.Id,
+								SubType = new {x.OneToOne, x.Name},
+								SubType2 = new
+								{
+									x.Id,
+									x.OneToOne,
+									SubType3 = new {x.Id, x.OneToOne}
+								},
+								x.OneToOne
+							}).FirstOrDefaultAsync());
+				Assert.That(entity.OneToOne, Is.Not.Null);
+				Assert.That(entity.SubType.OneToOne, Is.Not.Null);
+				Assert.That(entity.SubType2.OneToOne, Is.Not.Null);
+				Assert.That(entity.SubType2.SubType3.OneToOne, Is.Not.Null);
+			}
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH2064/OneToOneEntity.cs

@@ -0,0 +1,10 @@
+using System;
+
+namespace NHibernate.Test.NHSpecificTest.GH2064
+{
+	public class OneToOneEntity
+	{
+		public virtual Guid Id { get; set; }
+		public virtual string Name { get; set; }
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH2064/OneToOneSelectProjectionFixture.cs

@@ -0,0 +1,106 @@
+using System.Linq;
+using NHibernate.Cfg.MappingSchema;
+using NHibernate.Mapping.ByCode;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH2064
+{
+	[TestFixture]
+	public class OneToOneSelectProjectionFixture : TestCaseMappingByCode
+	{
+		protected override HbmMapping GetMappings()
+		{
+			var mapper = new ModelMapper();
+			mapper.Class<OneToOneEntity>(
+				rc =>
+				{
+					rc.Id(e => e.Id, m => m.Generator(Generators.Assigned));
+					rc.Property(e => e.Name);
+				});
+
+			mapper.Class<ParentEntity>(
+				rc =>
+				{
+					rc.Id(e => e.Id, m => m.Generator(Generators.GuidComb));
+					rc.Property(e => e.Name);
+					rc.OneToOne(e => e.OneToOne, m => { });
+				});
+
+			return mapper.CompileMappingForAllExplicitlyAddedEntities();
+		}
+
+		protected override void OnSetUp()
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				var nullableOwner = new ParentEntity() {Name = "Owner",};
+				var oneToOne = new OneToOneEntity() {Name = "OneToOne"};
+				nullableOwner.OneToOne = oneToOne;
+				session.Save(nullableOwner);
+				oneToOne.Id = nullableOwner.Id;
+				session.Save(oneToOne);
+				session.Flush();
+
+				transaction.Commit();
+			}
+		}
+
+		protected override void OnTearDown()
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				// The HQL delete does all the job inside the database without loading the entities, but it does
+				// not handle delete order for avoiding violating constraints if any. Use
+				// session.Delete("from System.Object");
+				// instead if in need of having NHibernate ordering the deletes, but this will cause
+				// loading the entities in the session.
+				session.CreateQuery("delete from System.Object").ExecuteUpdate();
+
+				transaction.Commit();
+			}
+		}
+
+		[Test]
+		public void QueryOneToOne()
+		{
+			using (var session = OpenSession())
+			{
+				var entity =
+					session
+						.Query<ParentEntity>()
+						.FirstOrDefault();
+				Assert.That(entity.OneToOne, Is.Not.Null);
+			}
+		}
+
+		[Test]
+		public void QueryOneToOneProjection()
+		{
+			using (var session = OpenSession())
+			{
+				var entity =
+					session
+						.Query<ParentEntity>()
+						.Select(
+							x => new
+							{
+								x.Id,
+								SubType = new {x.OneToOne, x.Name},
+								SubType2 = new
+								{
+									x.Id,
+									x.OneToOne,
+									SubType3 = new {x.Id, x.OneToOne}
+								},
+								x.OneToOne
+							}).FirstOrDefault();
+				Assert.That(entity.OneToOne, Is.Not.Null);
+				Assert.That(entity.SubType.OneToOne, Is.Not.Null);
+				Assert.That(entity.SubType2.OneToOne, Is.Not.Null);
+				Assert.That(entity.SubType2.SubType3.OneToOne, Is.Not.Null);
+			}
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH2064/ParentEntity.cs

@@ -0,0 +1,11 @@
+using System;
+
+namespace NHibernate.Test.NHSpecificTest.GH2064
+{
+	public class ParentEntity
+	{
+		public virtual Guid Id { get; set; }
+		public virtual string Name { get; set; }
+		public virtual OneToOneEntity OneToOne { get; set; }
+	}
+}

src/NHibernate/Async/Loader/Hql/QueryLoader.cs

@@ -76,7 +76,9 @@ protected override async Task<object[]> GetResultRowAsync(object[] row, DbDataRe
 				resultRow = new object[queryCols];
 				for (int i = 0; i < queryCols; i++)
 				{
-					resultRow[i] = await (ResultTypes[i].NullSafeGetAsync(rs, scalarColumns[i], session, null, cancellationToken)).ConfigureAwait(false);
+					resultRow[i] = _entityByResultTypeDic.TryGetValue(i, out var rowIndex)
+						? row[rowIndex]
+						: await (ResultTypes[i].NullSafeGetAsync(rs, scalarColumns[i], session, null, cancellationToken)).ConfigureAwait(false);
 				}
 			}
 			else

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

@@ -133,13 +133,6 @@ public void Prepare()
 		private IType[] ResolveConstructorArgumentTypes()
 		{
 			ISelectExpression[] argumentExpressions = CollectSelectExpressions();
-
-			if ( argumentExpressions == null ) 
-			{
-				// return an empty Type array
-				return Array.Empty<IType>();
-			}
-
 			IType[] types = new IType[argumentExpressions.Length];
 			for ( int x = 0; x < argumentExpressions.Length; x++ ) 
 			{

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

@@ -23,6 +23,8 @@ public class SelectClause : SelectExpressionList
 		private IType[] _queryReturnTypes;
 		private string[][] _columnNames;
 		private readonly List<FromElement> _fromElementsForLoad = new List<FromElement>();
+		private readonly Dictionary<int, int> _entityByResultTypeDic = new Dictionary<int, int>();
+
 		private ConstructorNode _constructorNode;
 		private string[] _aliases;
 		private int[] _columnNamesStartPositions;
@@ -134,19 +136,20 @@ public void InitializeExplicitSelectClause(FromClause fromClause)
 				if (expr.IsConstructor)
 				{
 					_constructorNode = (ConstructorNode)expr;
-					IList<IType> constructorArgumentTypeList = _constructorNode.ConstructorArgumentTypeList;
 					//sqlResultTypeList.addAll( constructorArgumentTypeList );
-					queryReturnTypeList.AddRange(constructorArgumentTypeList);
 					_scalarSelect = true;
 
-					for (int j = 1; j < _constructorNode.ChildCount; j++)
+					var ctorSelectExpressions = _constructorNode.CollectSelectExpressions();
+					for (int j = 0; j < ctorSelectExpressions.Length; j++)
 					{
-						ISelectExpression se = _constructorNode.GetChild(j) as ISelectExpression;
+						ISelectExpression se = ctorSelectExpressions[j];
 
-						if (se != null && IsReturnableEntity(se))
+						if (IsReturnableEntity(se))
 						{
-							_fromElementsForLoad.Add(se.FromElement);
+							AddEntityToProjection(queryReturnTypeList.Count, se);
 						}
+
+						queryReturnTypeList.Add(se.DataType);
 					}
 				}
 				else
@@ -163,10 +166,9 @@ public void InitializeExplicitSelectClause(FromClause fromClause)
 					{
 						_scalarSelect = true;
 					}
-
-					if (IsReturnableEntity(expr))
+					else if (IsReturnableEntity(expr))
 					{
-						_fromElementsForLoad.Add(expr.FromElement);
+						AddEntityToProjection(queryReturnTypeList.Count, expr);
 					}
 
 					// Always add the type to the return type list.
@@ -247,6 +249,12 @@ public void InitializeExplicitSelectClause(FromClause fromClause)
 			FinishInitialization( /*sqlResultTypeList,*/ queryReturnTypeList);
 		}
 
+		private void AddEntityToProjection(int resultIndex, ISelectExpression se)
+		{
+			_entityByResultTypeDic[resultIndex] = _fromElementsForLoad.Count;
+			_fromElementsForLoad.Add(se.FromElement);
+		}
+
 		private static FromElement GetOrigin(FromElement fromElement)
 		{
 			var realOrigin = fromElement.RealOrigin;
@@ -271,6 +279,11 @@ public IList<FromElement> FromElementsForLoad
 			get { return _fromElementsForLoad; }
 		}
 
+		/// <summary>
+		/// Maps QueryReturnTypes[key] to entities from FromElementsForLoad[value]
+		/// </summary>
+		internal IReadOnlyDictionary<int, int> EntityByResultTypeDic => _entityByResultTypeDic;
+
 		public bool IsScalarSelect
 		{
 			get { return _scalarSelect; }

src/NHibernate/Loader/Hql/QueryLoader.cs

@@ -47,6 +47,7 @@ public partial class QueryLoader : BasicLoader
 		private IType[] _cacheTypes;
 		private ISet<ICollectionPersister> _uncacheableCollectionPersisters;
 		private Dictionary<string, string[]>[] _collectionUserProvidedAliases;
+		private IReadOnlyDictionary<int, int> _entityByResultTypeDic;
 
 		public QueryLoader(QueryTranslatorImpl queryTranslator, ISessionFactoryImplementor factory, SelectClause selectClause)
 			: base(factory)
@@ -214,6 +215,7 @@ protected override IDictionary<string, string[]> GetCollectionUserProvidedAlias(
 		private void Initialize(SelectClause selectClause)
 		{
 			IList<FromElement> fromElementList = selectClause.FromElementsForLoad;
+			_entityByResultTypeDic = selectClause.EntityByResultTypeDic;
 
 			_hasScalars = selectClause.IsScalarSelect;
 			_scalarColumnNames = selectClause.ColumnNames;
@@ -401,7 +403,9 @@ protected override object[] GetResultRow(object[] row, DbDataReader rs, ISession
 				resultRow = new object[queryCols];
 				for (int i = 0; i < queryCols; i++)
 				{
-					resultRow[i] = ResultTypes[i].NullSafeGet(rs, scalarColumns[i], session, null);
+					resultRow[i] = _entityByResultTypeDic.TryGetValue(i, out var rowIndex)
+						? row[rowIndex]
+						: ResultTypes[i].NullSafeGet(rs, scalarColumns[i], session, null);
 				}
 			}
 			else