Additional optimization.

Author: fredericDelaporte

src/NHibernate/Async/Impl/ExpressionQueryImpl.cs

@@ -17,6 +17,7 @@
 using NHibernate.Hql.Ast.ANTLR;
 using NHibernate.Hql.Ast.ANTLR.Tree;
 using NHibernate.Hql.Ast.ANTLR.Util;
+using NHibernate.Linq;
 using NHibernate.Type;
 using NHibernate.Util;
 

src/NHibernate/Impl/ExpressionQueryImpl.cs

@@ -7,6 +7,7 @@
 using NHibernate.Hql.Ast.ANTLR;
 using NHibernate.Hql.Ast.ANTLR.Tree;
 using NHibernate.Hql.Ast.ANTLR.Util;
+using NHibernate.Linq;
 using NHibernate.Type;
 using NHibernate.Util;
 
@@ -27,7 +28,7 @@ protected ExpressionQueryImpl(
 			_isFilter = isFilter;
 		}
 
-		public IQueryExpression QueryExpression { get; private set; }
+		public IQueryExpression QueryExpression { get; }
 
 		protected readonly bool _isFilter;
 
@@ -81,10 +82,15 @@ protected override IQueryExpression ExpandParameters(IDictionary<string, TypedVa
 				return QueryExpression;
 			}
 
-			//TODO: Do we need to translate expression one more time here?
-			// This is not much an issue anymore: ExpressionQueryImpl are currently created only with NhLinqExpression
-			// which do cache their translation.
-			var newTree = ParameterExpander.Expand(QueryExpression.Translate(Session.Factory, _isFilter), map);
+			// Translating expression one more time here is not much an issue anymore: when using the default Linq
+			// provider, ExpressionQueryImpl are created only with NhLinqExpression, which do cache their translation.
+			var newTree = ParameterExpander.Expand(
+				QueryExpression is NhLinqExpression linqExpr ?
+					// Avoid cloning, the parameter expander does (and need to) clone too.
+					linqExpr.Translate(Session.Factory, _isFilter, false) :
+					// A custom Linq provider may supply something else than a NhLinqExpression, support it.
+					QueryExpression.Translate(Session.Factory, _isFilter),
+				map);
 			var key = new StringBuilder(QueryExpression.Key);
 
 			foreach (var pair in map)
@@ -201,7 +207,7 @@ private IASTNode Expand()
 			var parameters = ParameterDetector.LocateParameters(_tree, new HashSet<string>(_map.Keys));
 			var nodeMapping = new Dictionary<IASTNode, IEnumerable<IASTNode>>();
 
-			foreach (IASTNode param in parameters)
+			foreach (var param in parameters)
 			{
 				var paramName = param.GetChild(0);
 				var aliases = _map[paramName.Text];

src/NHibernate/Linq/NhLinqExpression.cs

@@ -67,6 +67,9 @@ public NhLinqExpression(Expression expression, ISessionFactoryImplementor sessio
 		}
 
 		public IASTNode Translate(ISessionFactoryImplementor sessionFactory, bool filter)
+			=> Translate(sessionFactory, filter, true);
+
+		public IASTNode Translate(ISessionFactoryImplementor sessionFactory, bool filter, bool yieldClone)
 		{
 			if (ExpressionToHqlTranslationResults != null)
 			{