Question

I was trying to write a user authentication system in Java. So I wrote some DAO class. First I did write a class named Persistence which is abstract. It is responsible for holding some common attributes. And wrote a class named User extending Persistence class. Those classes are –

  public abstract class Persistance {

     private Date createdDate;
     private Date lastUpdatedDate;
     private long version;
     private boolean  isDeleted;


    //getter and setters
 }

and the user class

 public class User extends  Persistance{
   private String username;
   private String password;
   private String passwordConfired;

  // getters and setters

 }

My questions are- what is the best way to write variable name, which one is good, createdDate or dateCreated, deleted or isDeleted etc.

And is this approach is okay or is there more good approach ?
And how to implement data versioning?

Answer 1

You are mixing a DAO (data access object) and a VO (value object) – also known as a DTO (data transfer object) – in the same class.

Example using an interface for DAO behavior (blammy and kpow might be webservice, oracle database, mysql database, hibernate, or anything meaningful):

public interface UserDTO
{
    boolean deleteUser(String userId);
    UserVO readUser(String userId);
    void updateUser(String userId, UserVO newValues);
}

package blah.blammy;
public class UserDTOImpl implements UserDTO
{
  ... implement it based on blammy.
}

package blah.kpow;
public class UserDTOImpl implements UserDTO
{
  ... implement it based on kpow.
}

Example VO:

public class UserVO
{
    String firstName;
    String lastName;
    String middleInitial;

    ... getters and setters.
}

I prefer to identify the target of the delete using an ID instead of a VO object. Also, it is possible that an update will change the target identified by user ID “smackdown” to have user ID “smackup”, so I generally pass an id and a VO.