I have this situation:

public class User {
 private String email;
 private String name;
 private String surname;
 private String username;
 private String password;
 /* getter and setter*/
}
/* ------- */
public T getByUniqueKey(String key, Object value) throws ArangoException {
String query = "FOR t IN " + getCollectionName() + " FILTER t." + key + " == @" + key + " RETURN t";
Map<String, Object> bindVars = new MapBuilder().put(key, value).get();
 return getConnection().executeQuery(query,
 bindVars, clazz, false, 0).getUniqueResult();
 }
/* ------ */

After calling the getByUniqueKey method, I would do like update the User object.
I cannot use the updateDocument method because I do not have the _id field. In fact,
_id and _key fields are available only when call method that returns DocumentEntity<T> or extends BaseDocument class.
If extends BaseDocument other fields like properties are serialized and saved to DB.
I've used recently this object mapper where each class extends ArangoDbDocument.
I could use this approach, however, would be redundant if the same class is used in a method that returns a DocumentEntity<T>

Any suggestions?