CSHARP-1470: propogate embedded array field prefixes correctly.

Author: craiggwilson

src/MongoDB.Driver.Tests/Linq/MongoQueryableTests.cs

@@ -864,6 +864,29 @@ from y in x.G
                 "{ $project: { F: '$C.E.F', Other: '$G.D', _id: 0 } }");
         }
 
+        [Test]
+        public void SelectMany_followed_by_a_group()
+        {
+            var first = from x in CreateQuery()
+                        from y in x.G
+                        select y;
+
+            var query = from f in first
+                        group f by f.D into g
+                        select new
+                        {
+                            g.Key,
+                            SumF = g.Sum(x => x.E.F)
+                        };
+
+            Assert(query,
+                4,
+                "{ $unwind: '$G' }",
+                "{ $project: { G: 1, _id: 0 } }",
+                "{ $group: { _id: '$G.D', __agg0: { $sum : '$G.E.F' } } }",
+                "{ $project: { Key: '$_id', SumF: '$__agg0', _id: 0 } }");
+        }
+
         [Test]
         public void Single()
         {

src/MongoDB.Driver/Linq/Processors/EmbeddedPipeline/EmbeddedPipelineBinder.cs

@@ -85,9 +85,18 @@ protected override Expression BindNonMethodCall(Expression node)
                 BsonSerializationInfo itemSerializationInfo;
                 if (arraySerializer != null && arraySerializer.TryGetItemSerializationInfo(out itemSerializationInfo))
                 {
-                    return new PipelineExpression(
-                        node,
-                        new DocumentExpression(itemSerializationInfo.Serializer));
+                    if (itemSerializationInfo.ElementName == null)
+                    {
+                        return new PipelineExpression(
+                            node,
+                            new DocumentExpression(itemSerializationInfo.Serializer));
+                    }
+                    else
+                    {
+                        return new PipelineExpression(
+                            node,
+                            new FieldExpression(itemSerializationInfo.ElementName, itemSerializationInfo.Serializer));
+                    }
                 }
             }
             else if (node.NodeType == ExpressionType.Constant)

src/MongoDB.Driver/Linq/Processors/Pipeline/MethodCallBinders/GroupByBinder.cs

@@ -62,13 +62,17 @@ private Expression BindKey(PipelineExpression pipeline, PipelineBindingContext b
 
         private Expression BuildProjector(PipelineBindingContext bindingContext, Expression idSelector, Expression elementSelector)
         {
+            var elementSerializer = bindingContext.GetSerializer(elementSelector.Type, elementSelector);
+            var elementFieldName = (elementSelector as IFieldExpression)?.FieldName;
+
             var serializerType = typeof(GroupingDeserializer<,>).MakeGenericType(
                 idSelector.Type,
                 elementSelector.Type);
             var serializer = (IBsonSerializer)Activator.CreateInstance(
                 serializerType,
                 bindingContext.GetSerializer(idSelector.Type, idSelector),
-                bindingContext.GetSerializer(elementSelector.Type, elementSelector));
+                bindingContext.GetSerializer(elementSelector.Type, elementSelector),
+                elementFieldName);
 
             return new DocumentExpression(serializer);
         }
@@ -100,13 +104,15 @@ System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
 
         private class GroupingDeserializer<TKey, TElement> : SerializerBase<IGrouping<TKey, TElement>>, IBsonDocumentSerializer, IBsonArraySerializer
         {
+            private readonly string _elementFieldName;
             private readonly IBsonSerializer _elementSerializer;
             private readonly IBsonSerializer _idSerializer;
 
-            public GroupingDeserializer(IBsonSerializer idSerializer, IBsonSerializer elementSerializer)
+            public GroupingDeserializer(IBsonSerializer idSerializer, IBsonSerializer elementSerializer, string elementFieldName)
             {
                 _idSerializer = idSerializer;
                 _elementSerializer = elementSerializer;
+                _elementFieldName = elementFieldName;
             }
 
             public override IGrouping<TKey, TElement> Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
@@ -144,7 +150,7 @@ public bool TryGetMemberSerializationInfo(string memberName, out BsonSerializati
 
             public bool TryGetItemSerializationInfo(out BsonSerializationInfo serializationInfo)
             {
-                serializationInfo = new BsonSerializationInfo(null, _elementSerializer, typeof(TElement));
+                serializationInfo = new BsonSerializationInfo(_elementFieldName, _elementSerializer, typeof(TElement));
                 return true;
             }
         }