Modification to allow Linq subqueries to have paging (OrderBy/Take) (#2480)

Fixes #2479

Author: ngbrown

src/NHibernate.Test/Async/Linq/WhereSubqueryTests.cs

@@ -11,9 +11,10 @@
 using System;
 using System.Linq;
 using System.Linq.Expressions;
+using NHibernate.Dialect;
 using NHibernate.DomainModel.Northwind.Entities;
-using NUnit.Framework;
 using NHibernate.Linq;
+using NUnit.Framework;
 
 namespace NHibernate.Test.Linq
 {
@@ -465,6 +466,27 @@ where subquery.Any(x => x.OrderId == order.OrderId)
 			Assert.That(query.Count, Is.EqualTo(61));
 		}
 
+		[Test(Description = "GH2479")]
+		public async Task OrdersWithSubquery11Async()
+		{
+			if (Dialect is MySQLDialect)
+				Assert.Ignore("MySQL does not support LIMIT in subqueries.");
+			if (Dialect is MsSqlCeDialect)
+				Assert.Ignore("MS SQL CE does not support sorting on a subquery.");
+
+			var ordersQuery = db.Orders
+			                    .OrderByDescending(x => x.OrderLines.Count).ThenBy(x => x.OrderId)
+			                    .Take(2);
+
+			var orderLineQuery = ordersQuery.SelectMany(x => x.OrderLines);
+			var productsNotInLargestOrders = await (db.Products
+			                                   .Where(x => orderLineQuery.All(p => p.Product != x))
+			                                   .OrderBy(x => x.ProductId)
+			                                   .ToListAsync());
+
+			Assert.That(productsNotInLargestOrders.Count, Is.EqualTo(49), nameof(productsNotInLargestOrders));
+		}
+
 		[Test(Description = "NH-2654")]
 		public async Task CategoriesWithDiscountedProductsAsync()
 		{

src/NHibernate.Test/Linq/WhereSubqueryTests.cs

@@ -1,7 +1,9 @@
 using System;
 using System.Linq;
 using System.Linq.Expressions;
+using NHibernate.Dialect;
 using NHibernate.DomainModel.Northwind.Entities;
+using NHibernate.Linq;
 using NUnit.Framework;
 
 namespace NHibernate.Test.Linq
@@ -509,6 +511,74 @@ where subquery.Any(x => x.OrderId == order.OrderId)
 			Assert.That(query.Count, Is.EqualTo(61));
 		}
 
+		[Test(Description = "GH2479")]
+		public void OrdersWithSubquery9()
+		{
+			if (Dialect is MySQLDialect)
+				Assert.Ignore("MySQL does not support LIMIT in subqueries.");
+
+			var ordersQuery = db.Orders
+			                    .Where(x => x.Employee.EmployeeId > 5)
+			                    .OrderBy(x => x.OrderId)
+			                    .Take(2);
+
+			var orderLinesFuture = db.OrderLines
+			                         .Where(x => ordersQuery.Any(o => o == x.Order))
+			                         .OrderBy(x => x.Id)
+			                         .ToFuture();
+
+			var orders = ordersQuery.ToFuture().ToList();
+			var orderLines = orderLinesFuture.ToList();
+
+			Assert.That(orders.Count, Is.EqualTo(2), nameof(orders));
+			Assert.That(orderLines.Count, Is.EqualTo(6), nameof(orderLines));
+		}
+
+		[Test(Description = "GH2479")]
+		public void OrdersWithSubquery10()
+		{
+			if (Dialect is MySQLDialect)
+				Assert.Ignore("MySQL does not support LIMIT in subqueries.");
+
+			var ordersQuery = db.Orders
+			                    .Where(x => x.Employee.EmployeeId > 5)
+			                    .OrderBy(x => x.OrderId)
+			                    .Take(2);
+
+			var productsQuery = ordersQuery.SelectMany(x => x.OrderLines).Select(x => x.Product);
+			var productsFuture = db.Products
+			                       .Where(x => productsQuery.Contains(x))
+			                       .OrderBy(x => x.ProductId)
+			                       .ToFuture();
+
+			var orders = ordersQuery.ToFuture().ToList();
+			var products = productsFuture.ToList();
+
+			Assert.That(orders.Count, Is.EqualTo(2), nameof(orders));
+			Assert.That(products.Count, Is.EqualTo(6), nameof(products));
+		}
+
+		[Test(Description = "GH2479")]
+		public void OrdersWithSubquery11()
+		{
+			if (Dialect is MySQLDialect)
+				Assert.Ignore("MySQL does not support LIMIT in subqueries.");
+			if (Dialect is MsSqlCeDialect)
+				Assert.Ignore("MS SQL CE does not support sorting on a subquery.");
+
+			var ordersQuery = db.Orders
+			                    .OrderByDescending(x => x.OrderLines.Count).ThenBy(x => x.OrderId)
+			                    .Take(2);
+
+			var orderLineQuery = ordersQuery.SelectMany(x => x.OrderLines);
+			var productsNotInLargestOrders = db.Products
+			                                   .Where(x => orderLineQuery.All(p => p.Product != x))
+			                                   .OrderBy(x => x.ProductId)
+			                                   .ToList();
+
+			Assert.That(productsNotInLargestOrders.Count, Is.EqualTo(49), nameof(productsNotInLargestOrders));
+		}
+
 		[Test(Description = "NH-2654")]
 		public void CategoriesWithDiscountedProducts()
 		{

src/NHibernate/Linq/GroupBy/PagingRewriter.cs

@@ -28,7 +28,7 @@ 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)
@@ -53,7 +53,8 @@ private static void FlattenSubQuery(SubQueryExpression subQueryExpression, Query
 				var where = new WhereClause(new SubQueryExpression(newSubQueryModel));
 				queryModel.BodyClauses.Add(where);
 
-				if (!queryModel.BodyClauses.OfType<OrderByClause>().Any())
+				if (!queryModel.BodyClauses.OfType<OrderByClause>().Any() && 
+					!(queryModel.ResultOperators.Count == 1 && queryModel.ResultOperators.All(x => x is AnyResultOperator || x is ContainsResultOperator || x is AllResultOperator)))
 				{
 					var orderByClauses = subQueryModel.BodyClauses.OfType<OrderByClause>();
 					foreach (var orderByClause in orderByClauses)