SkipAndTake (#15)

Author: StefH

src/System.Linq.Dynamic.Core/ExpressionParser.cs

@@ -183,6 +183,8 @@ interface IEnumerableSignatures
             void OrderBy(object selector);
             void OrderByDescending(object selector);
             void Contains(object selector);
+            void Skip(int count);
+            void Take(int count);
 
             //Executors
             void Single();
@@ -1389,7 +1391,7 @@ Expression ParseAggregate(Expression instance, Type elementType, string methodNa
 
             _parent = _it;
 
-            if (methodName == "Contains")
+            if (methodName == "Contains" || methodName == "Skip" || methodName == "Take")
             {
                 //for any method that acts on the parent element type, we need to specify the outerIt as scope.
                 _it = outerIt;
@@ -1426,7 +1428,7 @@ Expression ParseAggregate(Expression instance, Type elementType, string methodNa
                 typeArgs = new[] { elementType };
             }
 
-            if (signature.Name == "Contains")
+            if (signature.Name == "Contains" || signature.Name == "Take" || signature.Name == "Skip")
             {
                 args = new[] { instance, args[0] };
             }

test/System.Linq.Dynamic.Core.Tests/ExpressionTests.cs

@@ -8,6 +8,34 @@ namespace System.Linq.Dynamic.Core.Tests
 {
     public class ExpressionTests
     {
+        [Fact]
+        public void ExpressionTests_SkipAndTake()
+        {
+            //Arrange
+            var samples = User.GenerateSampleModels(3);
+            samples[0].Roles = null;
+            samples[1].Roles = new List<Role> { new Role(), new Role() };
+
+            var sampleQuery = samples.AsQueryable();
+
+            //Act
+            var expectedResult = sampleQuery.Select(x => new { SecondRole = x.Roles != null ? x.Roles.Skip(1).Take(1) : null }).ToArray();
+
+            var result = sampleQuery.Select("new ( iif(Roles != null, Roles.Skip(1).Take(1), null) as SecondRole )");
+
+            //Assert
+            var resultArray = result.ToDynamicArray();
+            for (int i = 0; i < expectedResult.Count(); i++)
+            {
+                var expectedEntry = expectedResult[i];
+                var entry = resultArray[i];
+                if (expectedEntry.SecondRole == null)
+                    Assert.Null(entry.SecondRole);
+                else
+                    Assert.Equal(expectedEntry.SecondRole.ToString(), entry.SecondRole.ToString());
+            }
+        }
+
         [Fact]
         public void ExpressionTests_StringConcatenation()
         {