CSHARP-1326: Fix issue when using IGrouping as IEnumerable.

Author: rstam

src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/NewListExpressionToAggregationExpressionTranslator.cs

@@ -34,13 +34,14 @@ public static AggregationExpression Translate(TranslationContext context, NewExp
             {
                 var argument = arguments[0];
                 var argumentType = argument.Type;
-                if (argumentType.IsConstructedGenericType && argumentType.GetGenericTypeDefinition() == typeof(IEnumerable<>))
+                if (argumentType.IsConstructedGenericType && argumentType.GetGenericTypeDefinition().Implements(typeof(IEnumerable<>)))
                 {
-                    var argumentItemType = argumentType.GetGenericArguments()[0];
+                    var enumerableInterface = argumentType.GetIEnumerableGenericInterface();
+                    var argumentItemType = enumerableInterface.GetGenericArguments()[0];
                     if (argumentItemType == listItemType)
                     {
                         var collectionExpression = argument;
-                        var collectionTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, collectionExpression);
+                        var collectionTranslation = ExpressionToAggregationExpressionTranslator.TranslateEnumerable(context, collectionExpression);
                         var listSerializerType = typeof(EnumerableInterfaceImplementerSerializer<,>).MakeGenericType(listType, listItemType);
                         var listItemSerializer = ArraySerializerHelper.GetItemSerializer(collectionTranslation.Serializer);
                         var listSerializer = (IBsonSerializer)Activator.CreateInstance(listSerializerType, listItemSerializer);

tests/MongoDB.Driver.Tests/Linq/Linq3ImplementationTests/Jira/CSharp1326Tests.cs

@@ -0,0 +1,87 @@
+/* Copyright 2010-present MongoDB Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System.Collections.Generic;
+using System.Linq;
+using FluentAssertions;
+using MongoDB.Bson;
+using MongoDB.Bson.Serialization.Attributes;
+using Xunit;
+
+namespace MongoDB.Driver.Tests.Linq.Linq3ImplementationTests.Jira
+{
+    public class CSharp1326Tests : Linq3IntegrationTest
+    {
+        [Fact]
+        public void Projection_of_ArrayOfDocuments_dictionary_keys_and_values_should_work()
+        {
+            var collection = CreateCollection();
+            var parentIds = new int[] { 1, 2, 3 };
+            var childrenFilter =
+                Builders<Child>.Filter.In(c => c.ParentId, parentIds) &
+                Builders<Child>.Filter.Eq(c => c.Gender, Gender.Male);
+
+            var aggregate = collection
+                .Aggregate()
+                .Match(childrenFilter)
+                .Group(c => c.ParentId, g => new KeyValuePair<int, List<Child>>(g.Key, new List<Child>(g)));
+
+            var stages = Translate(collection, aggregate);
+            AssertStages(
+                stages,
+                "{ $match : { ParentId : { $in : [1, 2, 3] }, Gender : 'Male' } }",
+                "{ $group : { _id : '$ParentId', _elements : { $push : '$$ROOT' } } }",
+                "{ $project : { Key : '$_id', Value : '$_elements', _id : 0 } }");
+
+            var results = aggregate.ToList().OrderBy(x => x.Key).ToList();
+            results[0].Key.Should().Be(1);
+            results[0].Value.Select(x => x.Id).Should().BeEquivalentTo(1, 2);
+            results[1].Key.Should().Be(2);
+            results[1].Value.Select(x => x.Id).Should().BeEquivalentTo(4);
+        }
+
+        private IMongoCollection<Child> CreateCollection()
+        {
+            var collection = GetCollection<Child>("Children");
+
+            CreateCollection(
+                collection,
+                new Child { Id = 1, ParentId = 1, Gender = Gender.Male },
+                new Child { Id = 2, ParentId = 1, Gender = Gender.Male },
+                new Child { Id = 3, ParentId = 1, Gender = Gender.Female },
+                new Child { Id = 4, ParentId = 2, Gender = Gender.Male },
+                new Child { Id = 5, ParentId = 4, Gender = Gender.Male });
+
+            return collection;
+        }
+
+        public class Parent
+        {
+            public int Id { get; set; }
+        }
+
+        public class Child
+        {
+            public int Id { get; set; }
+
+            public int ParentId { get; set; }
+
+            [BsonRepresentation(BsonType.String)]
+            public Gender Gender { get; set; }
+        }
+
+        public enum Gender { Male, Female };
+    }
+}