Make sure 'top' doesn't apply on a null collection

Author: ificator

src/Microsoft.AspNet.OData.Shared/Query/Expressions/SelectExpandBinder.cs

@@ -978,8 +978,12 @@ private Expression GetNullCheckExpression(IEdmNavigationProperty propertyToExpan
 
         // new CollectionWrapper<ElementType> { Instance = source.Select((ElementType element) => new Wrapper { }) }
         [SuppressMessage("Microsoft.Maintainability", "CA1502:AvoidExcessiveComplexity", Justification = "These are simple conversion function and cannot be split up.")]
-        private Expression ProjectCollection(Expression source, Type elementType,
-            SelectExpandClause selectExpandClause, IEdmStructuredType structuredType, IEdmNavigationSource navigationSource,
+        private Expression ProjectCollection(
+            Expression source,
+            Type elementType,
+            SelectExpandClause selectExpandClause,
+            IEdmStructuredType structuredType,
+            IEdmNavigationSource navigationSource,
             OrderByClause orderByClause,
             long? topOption,
             long? skipOption,
@@ -1005,9 +1009,10 @@ private Expression ProjectCollection(Expression source, Type elementType,
             //      (ElementType element) => new Wrapper { }
             LambdaExpression selector = Expression.Lambda(projection, element);
 
+            Expression modifiedSource = source;
             if (orderByClause != null)
             {
-                source = AddOrderByQueryForSource(source, orderByClause, elementType);
+                modifiedSource = AddOrderByQueryForSource(modifiedSource, orderByClause, elementType);
             }
 
             bool hasTopValue = topOption != null && topOption.HasValue;
@@ -1033,7 +1038,7 @@ private Expression ProjectCollection(Expression source, Type elementType,
                         bool alreadyOrdered = false;
                         foreach (var prop in properties)
                         {
-                            source = ExpressionHelpers.OrderByPropertyExpression(source, prop.Name, elementType, alreadyOrdered);
+                            modifiedSource = ExpressionHelpers.OrderByPropertyExpression(modifiedSource, prop.Name, elementType, alreadyOrdered);
                             if (!alreadyOrdered)
                             {
                                 alreadyOrdered = true;
@@ -1046,14 +1051,14 @@ private Expression ProjectCollection(Expression source, Type elementType,
             if (hasSkipvalue)
             {
                 Contract.Assert(skipOption.Value <= Int32.MaxValue);
-                source = ExpressionHelpers.Skip(source, (int)skipOption.Value, elementType,
+                modifiedSource = ExpressionHelpers.Skip(modifiedSource, (int)skipOption.Value, elementType,
                     _settings.EnableConstantParameterization);
             }
 
             if (hasTopValue)
             {
                 Contract.Assert(topOption.Value <= Int32.MaxValue);
-                source = ExpressionHelpers.Take(source, (int)topOption.Value, elementType,
+                modifiedSource = ExpressionHelpers.Take(modifiedSource, (int)topOption.Value, elementType,
                     _settings.EnableConstantParameterization);
             }
 
@@ -1066,12 +1071,12 @@ private Expression ProjectCollection(Expression source, Type elementType,
                     {
                         if (_settings.PageSize.HasValue)
                         {
-                            source = ExpressionHelpers.Take(source, _settings.PageSize.Value + 1, elementType,
+                            modifiedSource = ExpressionHelpers.Take(modifiedSource, _settings.PageSize.Value + 1, elementType,
                                 _settings.EnableConstantParameterization);
                         }
                         else if (_settings.ModelBoundPageSize.HasValue)
                         {
-                            source = ExpressionHelpers.Take(source, modelBoundPageSize.Value + 1, elementType,
+                            modifiedSource = ExpressionHelpers.Take(modifiedSource, modelBoundPageSize.Value + 1, elementType,
                                 _settings.EnableConstantParameterization);
                         }
                     }
@@ -1081,7 +1086,7 @@ private Expression ProjectCollection(Expression source, Type elementType,
             // expression
             //      source.Select((ElementType element) => new Wrapper { })
             var selectMethod = GetSelectMethod(elementType, projection.Type);
-            Expression selectedExpresion = Expression.Call(selectMethod, source, selector);
+            Expression selectedExpresion = Expression.Call(selectMethod, modifiedSource, selector);
 
             // Append ToList() to collection as a hint to LINQ provider to buffer correlated subqueries in memory and avoid executing N+1 queries
             if (_settings.EnableCorrelatedSubqueryBuffering)

test/UnitTest/Microsoft.AspNet.OData.Test.Shared/Query/Expressions/SelectExpandBinderTest.cs

@@ -289,6 +289,38 @@ public void ProjectAsWrapper_NullExpandedProperty_HasNullValueInProjectedWrapper
             Assert.Null(projectCustomer.Instance);
         }
 
+        [Fact]
+        public void ProjectAsWrapper_Collection_TopOnNullExpand()
+        {
+            // Arrange
+            _settings.HandleNullPropagation = HandleNullPropagationOption.True;
+
+            IEdmEntityType vipCustomer = _model.SchemaElements.OfType<IEdmEntityType>().First(c => c.Name == "QueryVipCustomer");
+            IEdmNavigationProperty specialOrdersNav = vipCustomer.DeclaredNavigationProperties().Single(c => c.Name == "SpecialOrders");
+            ExpandedNavigationSelectItem expandItem = new ExpandedNavigationSelectItem(
+                new ODataExpandPath(new NavigationPropertySegment(specialOrdersNav, navigationSource: _orders)),
+                _orders,
+                selectAndExpand: null,
+                filterOption: null,
+                orderByOption: null,
+                topOption: 10,
+                skipOption: null,
+                countOption: null,
+                searchOption: null,
+                levelsOption: null);
+            SelectExpandClause selectExpand = new SelectExpandClause(new SelectItem[] { expandItem }, allSelected: true);
+
+            QueryVipCustomer customer = new QueryVipCustomer();
+            Expression source = Expression.Constant(customer);
+
+            // Act
+            Expression projection = _binder.ProjectAsWrapper(source, selectExpand, vipCustomer, _customers);
+
+            // Assert
+            IEnumerable<SelectExpandWrapper<QueryOrder>> projectedOrders = Expression.Lambda(projection).Compile().DynamicInvoke() as IEnumerable<SelectExpandWrapper<QueryOrder>>;
+            Assert.Null(projectedOrders);
+        }
+
         [Fact]
         public void ProjectAsWrapper_Collection_ProjectedValueNullAndHandleNullPropagationTrue()
         {