Fix SelectMany when using JArray (#585)

Author: StefH

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

@@ -1927,11 +1927,13 @@ private static IQueryable SelectManyInternal(IQueryable source, ParsingConfig co
                 // lambda.Body.Type.GetGenericArguments()[0] when used over an array as GetGenericArguments() returns an empty array.
                 if (lambda.Body.Type.IsArray)
                 {
+                    // In case of an Array, get the type via GetElementType().
                     resultType = lambda.Body.Type.GetElementType();
                 }
                 else
                 {
-                    resultType = lambda.Body.Type.GetGenericArguments()[0];
+                    var genericArguments = lambda.Body.Type.GetGenericArguments();
+                    resultType = genericArguments.Any() ? genericArguments[0] : typeof(object);
                 }
             }
 

test/System.Linq.Dynamic.Core.Tests/QueryableTests.SelectMany.cs

@@ -1,6 +1,8 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.Linq.Dynamic.Core.Tests.Helpers.Models;
+using FluentAssertions;
+using Newtonsoft.Json.Linq;
 using Xunit;
 
 namespace System.Linq.Dynamic.Core.Tests
@@ -103,6 +105,22 @@ public void SelectMany_Dynamic_IntoType()
             Assert.Equal(queryNormal, queryDynamic);
         }
 
+        [Fact]
+        public void SelectMany_Dynamic_OverJArray_TResult()
+        {
+            // Arrange
+            var array1 = JArray.Parse("[1,2,3]");
+            var array2 = JArray.Parse("[4,5,6]");
+
+            // Act
+            var expectedResult = new[] { array1, array2 }.SelectMany(it => it).ToArray();
+            var result = new[] { array1, array2 }.AsQueryable().SelectMany("it").ToDynamicArray<JToken>();
+
+            // Assert
+            result.Should().BeEquivalentTo(expectedResult);
+            // result.Should().HaveCount(6).And.Subject.Select(j => j.Value).Should().ContainInOrder(new[] { 1, 2, 3, 4, 5, 6 });
+        }
+
         [Fact]
         public void SelectMany_Dynamic_OverArray_TResult()
         {
@@ -119,6 +137,21 @@ public void SelectMany_Dynamic_OverArray_TResult()
             Assert.Equal(expectedResult, result);
         }
 
+        [Fact]
+        public void SelectMany_Dynamic_OverArray_Int()
+        {
+            var testList = new[]
+            {
+                new[] { 1, 2, 3 },
+                new[] { 4, 5, 6 }
+            };
+
+            var expectedResult = testList.SelectMany(it => it).ToList();
+            var result = testList.AsQueryable().SelectMany<int>("it").ToList();
+
+            Assert.Equal(expectedResult, result);
+        }
+
         [Fact]
         public void SelectMany_Dynamic_OverArray_IntoType()
         {