public Person_login createPerson(Person_login p) {
   DBObject doc = PersonConverter.toDBObject(p);
   this.col.insert(doc);
   ObjectId id = (ObjectId) doc.get("_id");
   p.setId(id.toString());
   return p;
 }
 public List<Person_login> readAllPerson() {
   List<Person_login> data = new ArrayList<Person_login>();
   DBCursor cursor = col.find();
   while (cursor.hasNext()) {
     DBObject doc = cursor.next();
     Person_login p = PersonConverter.toPerson(doc);
     data.add(p);
   }
   return data;
 }
  public Person_login getPerson(String email) {

    DBObject query = BasicDBObjectBuilder.start().append("email", email).get();

    DBObject data = this.col.findOne(query);
    if (data == null) {
      return null;
    } else {

      return PersonConverter.toPerson(data);
    }
  }
 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));
 }