CSHARP-1604: support downcasting.

Author: craiggwilson

src/MongoDB.Driver.Tests/UpdateDefinitionBuilderTests.cs

@@ -1,4 +1,4 @@
-/* Copyright 2010-2015 MongoDB Inc.
+/* Copyright 2010-2016 MongoDB Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
@@ -509,6 +509,18 @@ public void Set_Typed()
             Assert(subject.Set("Age", 1), "{$set: {age: 1}}");
         }
 
+        [Test]
+        public void Set_Typed_with_cast()
+        {
+            var subject = CreateSubject<Message>();
+
+            Assert(subject.Set(x => ((SmsMessage)x).PhoneNumber, "1234567890"), "{$set: {pn: '1234567890'}}");
+
+            var subject2 = CreateSubject<Person>();
+
+            Assert(subject2.Set(x => ((SmsMessage)x.Message).PhoneNumber, "1234567890"), "{$set: {'m.pn': '1234567890'}}");
+        }
+
         [Test]
         public void SetOnInsert()
         {
@@ -576,12 +588,25 @@ private class Person
             public DateTime LastUpdated { get; set; }
             [BsonElement("pets")]
             public List<Pet> Pets { get; set; }
+
+            [BsonElement("m")]
+            public Message Message { get; set; }
         }
 
         private class Pet
         {
             [BsonElement("name")]
             public string Name { get; set; }
         }
+
+        private abstract class Message
+        {
+        }
+
+        private class SmsMessage : Message
+        {
+            [BsonElement("pn")]
+            public string PhoneNumber { get; set; }
+        }
     }
 }

src/MongoDB.Driver/Linq/Expressions/FieldAsDocumentExpression.cs

@@ -1,4 +1,4 @@
-/* Copyright 2015 MongoDB Inc.
+/* Copyright 2015-2016 MongoDB Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
@@ -60,7 +60,7 @@ public override IBsonSerializer Serializer
 
         public override Type Type
         {
-            get { return _expression.Type; }
+            get { return _serializer.ValueType; }
         }
 
         public override string ToString()

src/MongoDB.Driver/Linq/Processors/SerializationBinder.cs

@@ -187,10 +187,44 @@ protected override Expression VisitUnary(UnaryExpression node)
             var newNode = (UnaryExpression)base.VisitUnary(node);
             if (newNode.NodeType == ExpressionType.Convert || newNode.NodeType == ExpressionType.ConvertChecked)
             {
+                // handle unnecessary convert expressions
                 if (newNode.Method == null && !newNode.IsLiftedToNull && newNode.Type.IsAssignableFrom(newNode.Operand.Type))
                 {
                     return newNode.Operand;
                 }
+
+                // handle downcast convert expressions
+                if (newNode.Operand.Type.IsAssignableFrom(newNode.Type))
+                {
+                    var serializationExpression = newNode.Operand as SerializationExpression;
+                    if (serializationExpression != null)
+                    {
+                        var serializer = _bindingContext.GetSerializer(newNode.Type, newNode);
+                        switch (serializationExpression.ExtensionType)
+                        {
+                            case ExtensionExpressionType.ArrayIndex:
+                                return new ArrayIndexExpression(
+                                    ((ArrayIndexExpression)serializationExpression).Array,
+                                    ((ArrayIndexExpression)serializationExpression).Index,
+                                    serializer);
+                            case ExtensionExpressionType.Collection:
+                                return new CollectionExpression(
+                                    ((CollectionExpression)serializationExpression).CollectionNamespace,
+                                    serializer);
+                            case ExtensionExpressionType.Document:
+                                return new DocumentExpression(serializer);
+                            case ExtensionExpressionType.Field:
+                                return new FieldExpression(
+                                    ((FieldExpression)serializationExpression).FieldName,
+                                    serializer);
+                            case ExtensionExpressionType.FieldAsDocument:
+                                return new FieldAsDocumentExpression(
+                                    ((FieldAsDocumentExpression)serializationExpression).Expression,
+                                    ((FieldAsDocumentExpression)serializationExpression).FieldName,
+                                    serializer);
+                        }
+                    }
+                }
             }
 
             return newNode;