Dictionary<string, object>-to-BsonDocument conversion omitting _t field

Question

I'm using ToBsonDocument extension method from MongoDB.Bson to convert this Dictionary:

        var dictionary = new Dictionary<string, object> {{"person", new Dictionary<string, object> {{"name", "John"}}}};
        var document = dictionary.ToBsonDocument();

And here's the resulting document:

  { "person" : 
      { "_t" : "System.Collections.Generic.Dictionary`2[System.String,System.Object]", 
        "_v" : { "name" : "John" } } }

Is there a way to get rid of these _t/_v stuff? I would like the resulting document to look like this:

  { "person" : { "name" : "John" } }

---

UPD: I've found the code in DictionaryGenericSerializer:

if (nominalType == typeof(object))
{
    var actualType = value.GetType();
    bsonWriter.WriteStartDocument();
    bsonWriter.WriteString("_t", TypeNameDiscriminator.GetDiscriminator(actualType));
    bsonWriter.WriteName("_v");
    Serialize(bsonWriter, actualType, value, options); // recursive call replacing nominalType with actualType
    bsonWriter.WriteEndDocument();
    return;
}

So, it seems that there are not too many options with this serializer when the value type is object.

Answer 1

You shall first serialize to JSON and then to BSON,

var jsonDoc = Newtonsoft.Json.JsonConvert.SerializeObject(dictionary);
var bsonDoc = MongoDB.Bson.Serialization.BsonSerializer.Deserialize<BsonDocument>(jsonDoc);

Answer 2

That is happen because you specify object type for dictionary values, but actually use Dictionary<string, object> type for the particular record value. Therefore, CSharp driver saves the full name of concrete type to deserialize this document properly in future. You can also read more about it here: Serialize Documents with the CSharp Driver: Polymorphic Classes and Discriminators

To achieve desired result you should specify concrete type for dictionary values:

var dictionary = new Dictionary<string, Dictionary<string, object>>
{
    { "person", new Dictionary<string, object> { { "name", "John" } } }
};
var document = dictionary.ToBsonDocument();