I need to serialize a BsonDocument using the DataContractSerializer.
I have a class Play that has a BsonDocument (see stub below).

[BsonIgnoreExtraElements]
[DataContract(Namespace="f1")]
public class Play
{
...
[DataMember][BsonElement] public BsonDocument OD

}

Note: the first element in the BsonDocument is a BsonInt32.

When using the DataContractSerializer, I get the following error:
Type 'MongoDB.Bson.BsonInt32' with data contract name 'BsonInt32:http://schemas.datacontract.org/2004/07/MongoDB.Bson' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.