NH-3944 - preliminary work, Nh clauses eliminated.

Author: fredericDelaporte

src/NHibernate/Linq/Clauses/NhHavingClause.cs

@@ -2,7 +2,6 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Linq.Expressions;
-using NHibernate.Linq.Clauses;
 using NHibernate.Linq.ReWriters;
 using NHibernate.Linq.Visitors;
 using Remotion.Linq;
@@ -43,29 +42,26 @@ public static class AggregatingGroupByRewriter
 				typeof (CacheableResultOperator)
 			};
 
-		public static void ReWrite(QueryModel queryModel)
+		public static void ReWrite(QueryModel queryModel, VisitorParameters parameters)
 		{
-			var subQueryExpression = queryModel.MainFromClause.FromExpression as SubQueryExpression;
-
-			if (subQueryExpression != null)
+			if (queryModel.MainFromClause.FromExpression is SubQueryExpression subQueryExpression)
 			{
 				var operators = subQueryExpression.QueryModel.ResultOperators
 					.Where(x => !QueryReferenceExpressionFlattener.FlattenableResultOperators.Contains(x.GetType()))
 					.ToArray();
 
 				if (operators.Length == 1)
 				{
-					var groupBy = operators[0] as GroupResultOperator;
-					if (groupBy != null)
+					if (operators[0] is GroupResultOperator groupBy)
 					{
-						FlattenSubQuery(queryModel, subQueryExpression.QueryModel, groupBy);
+						FlattenSubQuery(queryModel, subQueryExpression.QueryModel, groupBy, parameters);
 						RemoveCostantGroupByKeys(queryModel, groupBy);
 					}
 				}
 			}
 		}
 
-		private static void FlattenSubQuery(QueryModel queryModel, QueryModel subQueryModel, GroupResultOperator groupBy)
+		private static void FlattenSubQuery(QueryModel queryModel, QueryModel subQueryModel, GroupResultOperator groupBy, VisitorParameters parameters)
 		{
 			foreach (var resultOperator in queryModel.ResultOperators.Where(resultOperator => !AcceptableOuterResultOperators.Contains(resultOperator.GetType())))
 			{
@@ -81,11 +77,9 @@ private static void FlattenSubQuery(QueryModel queryModel, QueryModel subQueryMo
 				clause.TransformExpressions(s => GroupBySelectClauseRewriter.ReWrite(s, groupBy, subQueryModel));
 
 				//all outer where clauses actually are having clauses
-				var whereClause = clause as WhereClause;
-				if (whereClause != null)
+				if (clause is WhereClause whereClause)
 				{
-					queryModel.BodyClauses.RemoveAt(i);
-					queryModel.BodyClauses.Insert(i, new NhHavingClause(whereClause.Predicate));
+					parameters.AddHavingClause(whereClause);
 				}
 			}
 

src/NHibernate/Linq/Clauses/NhJoinClause.cs

@@ -9,17 +9,16 @@ namespace NHibernate.Linq.GroupBy
 {
 	internal static class PagingRewriter
 	{
-		private static readonly System.Type[] PagingResultOperators = new[]
-																		  {
-																			  typeof (SkipResultOperator),
-																			  typeof (TakeResultOperator),
-																		  };
+		private static readonly System.Type[] PagingResultOperators =
+			new[]
+			{
+				typeof (SkipResultOperator),
+				typeof (TakeResultOperator),
+			};
 
 		public static void ReWrite(QueryModel queryModel)
 		{
-			var subQueryExpression = queryModel.MainFromClause.FromExpression as SubQueryExpression;
-
-			if (subQueryExpression != null &&
+			if (queryModel.MainFromClause.FromExpression is SubQueryExpression subQueryExpression &&
 				subQueryExpression.QueryModel.ResultOperators.All(x => PagingResultOperators.Contains(x.GetType())))
 			{
 				FlattenSubQuery(subQueryExpression, queryModel);
@@ -28,7 +27,7 @@ public static void ReWrite(QueryModel queryModel)
 
 		private static void FlattenSubQuery(SubQueryExpression subQueryExpression, QueryModel queryModel)
 		{
-			// we can not flattern subquery if outer query has body clauses.
+			// we can not flatten subquery if outer query has body clauses.
 			var subQueryModel = subQueryExpression.QueryModel;
 			var subQueryMainFromClause = subQueryModel.MainFromClause;
 			if (queryModel.BodyClauses.Count == 0)
@@ -46,9 +45,12 @@ private static void FlattenSubQuery(SubQueryExpression subQueryExpression, Query
 			{
 				var cro = new ContainsResultOperator(new QuerySourceReferenceExpression(subQueryMainFromClause));
 
+				// Cloning may cause having/join/with clauses listed in VisitorParameters to no more be matched.
+				// Not a problem for now, because those clauses imply a projection, which is not supported
+				// by the "new WhereClause(new SubQueryExpression(newSubQueryModel))" below.
 				var newSubQueryModel = subQueryModel.Clone();
 				newSubQueryModel.ResultOperators.Add(cro);
-				newSubQueryModel.ResultTypeOverride = typeof (bool);
+				newSubQueryModel.ResultTypeOverride = typeof(bool);
 
 				var where = new WhereClause(new SubQueryExpression(newSubQueryModel));
 				queryModel.BodyClauses.Add(where);