BsonClassMapSerializer already registered for AbstractClassSerializer

Question

I'm using the Mongo c# driver 2.0 and am running into BsonSerializer registration issues when registering AbstractClassSerializers for my Id value objects.

MongoDB.Bson.BsonSerializationException: There is already a serializer registered for type HistoricalEventId.

When I peek into the BsonSerializer I'm seeing that a BsonClassMapSerializer is already registered for my type.

I'm assuming that a BsonClassMapSerializer is being created for my entity types and it's also creating a BsonClassMapSerializer for the Id field as well. Has anyone run into this before? The Bson serializer code is shown below if that helps.

Sorry if the formatting is wrong, c# doesn't seem to be showing up well.

HistoricalEventIdBsonSerializer

public class HistoricalEventIdBsonSerializer : ToObjectIdBsonSerializer<HistoricalEventId>
{
    public override HistoricalEventId CreateObjectFromObjectId(ObjectId serializedObj)
    {
        HistoricalEventId parsedObj;
        HistoricalEventId.TryParse(serializedObj, out parsedObj);
        return parsedObj;
    }
}

ToObjectIdBsonSerializer

public abstract class ToObjectIdBsonSerializer<T> : AbstractClassSerializer<T> where T : class
{
    private static readonly Type _convertibleType = typeof(IConvertible<ObjectId>);
    public abstract T CreateObjectFromObjectId(ObjectId serializedObj);

    public override T Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
    {
        var bsonType = context.Reader.GetCurrentBsonType();
        ObjectId value;
        switch (bsonType)
        {
            case BsonType.Undefined:
                value = ObjectId.Empty;
                context.Reader.ReadUndefined();
                break;
            case BsonType.Null:
                value = ObjectId.Empty;
                context.Reader.ReadNull();
                break;
            case BsonType.ObjectId:
                value = context.Reader.ReadObjectId();
                break;
            case BsonType.String:
                value = new ObjectId(context.Reader.ReadString());
                break;
            default:
                throw new NotSupportedException("Unable to create the type " + 
                    args.NominalType.Name + " from the bson type " + bsonType + ".");
        }
        return this.CreateObjectFromObjectId(value);
    }

    public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args, T value)
    {
        if (value == null)
        {
            context.Writer.WriteObjectId(ObjectId.Empty);
        }
        else
        {
            if (!_convertibleType.IsAssignableFrom(args.NominalType))
            {
                throw new NotSupportedException("The type " + args.NominalType.Name + 
                    " must implement the " + _convertibleType.Name + " interface.");
            }
            var typedObj = (IConvertible<ObjectId>)value;
            context.Writer.WriteObjectId(typedObj.ToValueType());
        }
    }

}

IConvertible

public interface IConvertible<out T>
{
    T ToValueType();
}

Answer 1

My assumption must have been correct because I just fixed this by doing the BsonSerializer registration before creating the MongoClient and getting the database. Hopefully this will help someone else.