def oid(v = nil)
      return BSON::ObjectId.new if v.nil?; BSON::ObjectId.from_string(v) rescue v
    end
def oid(v = nil)
      return BSON::ObjectId.new if v.nil?; BSON::ObjectId.from_string(v) rescue v
    end
Convert to BSON ObjectId or make a new one