public void deletePerson(Person_login p) {
   DBObject query = BasicDBObjectBuilder.start().append("_id", new ObjectId(p.getId())).get();
   this.col.remove(query);
 }
 public Person_login readPerson(Person_login p) {
   DBObject query = BasicDBObjectBuilder.start().append("_id", new ObjectId(p.getId())).get();
   DBObject data = this.col.findOne(query);
   return PersonConverter.toPerson(data);
 }
 public void updatePerson(Person_login p) {
   DBObject query = BasicDBObjectBuilder.start().append("_id", new ObjectId(p.getId())).get();
   this.col.update(query, PersonConverter.toDBObject(p));
 }