Make previously HQL:ed expressions automatic candidates in SELECT

src/NHibernate/Linq/Visitors/QueryModelVisitor.cs

@@ -111,6 +111,7 @@ public static ExpressionToHqlTranslationResults GenerateHqlQuery(QueryModel quer
 		}
 
 		private readonly IntermediateHqlTree _hqlTree;
+		private readonly HashSet<Expression> _hqlCandidates;
 		private readonly NhLinqExpressionReturnType? _rootReturnType;
 		private static readonly ResultOperatorMap ResultOperatorMap;
 		private bool _serverSide = true;
@@ -165,6 +166,7 @@ private QueryModelVisitor(VisitorParameters visitorParameters, bool root, QueryM
 			_root = root;
 			_rootReturnType = root ? rootReturnType : null;
 			_hqlTree = new IntermediateHqlTree(root, _queryMode);
+			_hqlCandidates = new HashSet<Expression>();
 		}
 
 		private void Visit()
@@ -476,7 +478,7 @@ public override void VisitSelectClause(SelectClause selectClause, QueryModel que
 
 		private HqlSelect GetSelectClause(Expression selectClause)
 		{
-			var visitor = new SelectClauseVisitor(typeof(object[]), VisitorParameters);
+			var visitor = new SelectClauseVisitor(typeof(object[]), VisitorParameters, _hqlCandidates);
 
 			visitor.VisitSelector(selectClause, !_root);
 
@@ -537,7 +539,7 @@ private void VisitDeleteClause(Expression expression)
 				return;
 
 			// We only need to check there is no unexpected select, for avoiding silently ignoring them.
-			var visitor = new SelectClauseVisitor(typeof(object[]), VisitorParameters);
+			var visitor = new SelectClauseVisitor(typeof(object[]), VisitorParameters, new HashSet<Expression>());
 			visitor.VisitSelector(expression);
 
 			if (visitor.ProjectionExpression != null)
@@ -566,6 +568,7 @@ public override void VisitOrderByClause(OrderByClause orderByClause, QueryModel
 					: (HqlDirectionStatement)_hqlTree.TreeBuilder.Descending();
 
 				_hqlTree.AddOrderByClause(orderBy, direction);
+				_hqlCandidates.Add(clause.Expression);
 			}
 		}
 

src/NHibernate/Linq/Visitors/SelectClauseVisitor.cs

@@ -16,14 +16,22 @@ public class SelectClauseVisitor : RelinqExpressionVisitor
 		private HashSet<Expression> _hqlNodes;
 		private readonly ParameterExpression _inputParameter;
 		private readonly VisitorParameters _parameters;
+		private readonly HashSet<Expression> _hqlCandidates;
 		private int _iColumn;
 		private List<HqlExpression> _hqlTreeNodes = new List<HqlExpression>();
 		private readonly HqlGeneratorExpressionVisitor _hqlVisitor;
 
-		public SelectClauseVisitor(System.Type inputType, VisitorParameters parameters)
+		// Since v5.6
+		[Obsolete("Use overload providing expressions to be executed with HQL.")]
+		public SelectClauseVisitor(System.Type inputType, VisitorParameters parameters) :
+			this(inputType, parameters, new HashSet<Expression>())
+		{ }
+
+		public SelectClauseVisitor(System.Type inputType, VisitorParameters parameters, HashSet<Expression> hqlCandidates)
 		{
 			_inputParameter = Expression.Parameter(inputType, "input");
 			_parameters = parameters;
+			_hqlCandidates = hqlCandidates;
 			_hqlVisitor = new HqlGeneratorExpressionVisitor(_parameters);
 		}
 
@@ -69,9 +77,9 @@ public void VisitSelector(Expression expression, bool isSubQuery)
 
 			if (distinct != null)
 			{
-				var treeNodes = new List<HqlTreeNode>(_hqlTreeNodes.Count + 1) {_hqlTreeBuilder.Distinct()};
+				var treeNodes = new List<HqlTreeNode>(_hqlTreeNodes.Count + 1) { _hqlTreeBuilder.Distinct() };
 				treeNodes.AddRange(_hqlTreeNodes);
-				_hqlTreeNodes = new List<HqlExpression>(1) {_hqlTreeBuilder.ExpressionSubTreeHolder(treeNodes)};
+				_hqlTreeNodes = new List<HqlExpression>(1) { _hqlTreeBuilder.ExpressionSubTreeHolder(treeNodes) };
 			}
 		}
 
@@ -82,7 +90,7 @@ public override Expression Visit(Expression expression)
 				return null;
 			}
 
-			if (_hqlNodes.Contains(expression))
+			if (_hqlNodes.Contains(expression) || _hqlCandidates.Contains(expression))
 			{
 				// Pure HQL evaluation
 				_hqlTreeNodes.Add(_hqlVisitor.Visit(expression).AsExpression());