How to persist an Object

[Pramod Kumar]

Hi,

I need to modify a record in db, I have class with getters and setters and I am persisting this Object to db, I am able to insert data thru em.persist(user);

user is the object of that class, now I need to update the data in db I am using em.merge(user); now throwing IllegalArgumentException and think that object need to be persisted before doing update. How to persist this object.

Thanks,

[Paul Sturrock]

Is this Hibernate we are talking about? Or another ORM?

[Pramod Kumar]

This is in Hibernate EntityManager and JPA

[Cameron Wallace McKenzie]

Given this simple JPA annotated POJO:

  @Entity
@Table (name="user", schema="examscam")
public class User {
 
  private int id;
  private String password;
  private String loginName;
 
  @Id
  @GeneratedValue 
  @Column (name="id")
  public int getId() {return id;}
  public void setId(int id) {this.id = id;}
 
  @Column (name="login_name")
  public String getLoginName() {return loginName;}
  public void setLoginName(String loginName) {
    this.loginName = loginName;
  }
 
  @Column (name="password")
  public String getPassword() {return password;}
  public void setPassword(String password) {
    this.password = password;
  }
  
  public static void main(String args[]){  &&&  }
 
}
  

It can be persisted to the database, updated, retrieved and deleted with the following code which focusses on the basic CRUD operations:

 
public class CrudRunner {
 public static void main(String[] args) {
  CrudRunner.create();CrudRunner.retrieve();
  CrudRunner.retrieveFromId(1);CrudRunner.updateAll();
  CrudRunner.deleteAll();
 }
 public static void create() {
  AnnotationConfiguration config = new AnnotationConfiguration();
  config.addAnnotatedClass(User.class);
  SessionFactory factory= config.configure().buildSessionFactory();
  Session session = factory.getCurrentSession();
  session.beginTransaction();
  User user = new User();
  user.setLoginName("mj");user.setPassword("abc123");
  session.save(user);
  session.getTransaction().commit();
 }
 
 public static void retrieve() {
  AnnotationConfiguration config = new AnnotationConfiguration();
  config.addAnnotatedClass(User.class);
  SessionFactory factory= config.configure().buildSessionFactory();
  Session session = factory.getCurrentSession();
  session.beginTransaction();
  Query queryResult = session.createQuery("from User");
  java.util.List allUsers;
  allUsers = queryResult.list();
  for (int i = 0; i < allUsers.size(); i++) {
   User user = (User) allUsers.get(i);
  }
 System.out.println("Database contents delivered..."); 
 }
 
 public static User retrieveFromId(int idValue) {
  AnnotationConfiguration config = new AnnotationConfiguration();
  config.addAnnotatedClass(User.class);
  SessionFactory factory= config.configure().buildSessionFactory();
  Session session = factory.getCurrentSession();
  session.beginTransaction();/*lets hope an id of 1 exists!*/
  String queryString = "from User where id = :id";
  Query query = session.createQuery(queryString);
  query.setInteger("id", idValue);
  Object queryResult = query.uniqueResult();
  User user = (User)queryResult;session.getTransaction().commit();
  return user;
 }
 
 
 public static void updateAll() {
  AnnotationConfiguration config = 
                           new AnnotationConfiguration();
  config.addAnnotatedClass(User.class);
  SessionFactory factory= 
                  config.configure().buildSessionFactory();
  Session session = factory.getCurrentSession();
  session.beginTransaction();
  List allUsers;
  System.out.println("Updating all records...");
  Query queryResult = session.createQuery("from User");
  allUsers = queryResult.list(); 
  System.out.println("# of rows: "+ allUsers.size());
  for (int i = 0; i < allUsers.size(); i++) {
   User user = (User) allUsers.get(i);
   System.out.println(user);
   user.setPassword("password");
   session.update(user);
  }
  System.out.println("Database contents updated...");
  session.getTransaction().commit();
 }
 public static void deleteAll() {
  AnnotationConfiguration config =  new AnnotationConfiguration();
  config.addAnnotatedClass(User.class);
  SessionFactory factory=config.configure().buildSessionFactory();
  Session session = factory.getCurrentSession();
  List allUsers;
  session.beginTransaction();
  Query queryResult = session.createQuery("from User");
  allUsers = queryResult.list(); 
  for (int i = 0; i < allUsers.size(); i++) {
   User user = (User) allUsers.get(i);
   System.out.println(user);
   session.delete(user);
  }
  session.getTransaction().commit();
 }
}
   

Is that what you were looking for?
[ October 25, 2007: Message edited by: Cameron McKenzie ]

[Mark Spritzler]

Ouch.

In Cameron's example he is creating a SessionFactory in each method. In a production application you will want to only create it once and have the entire application share that one and only one instance. As SessionFactory objects are heavy-weight objects. Now Session objects are light-weight.

And in defense of Cameron's example, there really is only one mapped class, so the SessionFactory isn't as heavy as it would be in a real application.

Mark

[Cameron Wallace McKenzie]

Good point, Mark. There's actually a chapter in my Hibernate book that explores just that point, along with other optimizations around the SessionFactory, Session, and the Hibernate Core in general.

The example is purely for andragogical purposes. Each method is contains all of the information needed to perform the database interaction, without calling any helper classes or singleton methods or anything like that.

When you're learning, I think it's good to see as much of the plumbing as possible. In production, it's another story.

-Cameron McKenzie