How to implement update () method in DAO using EntityManager (JPA)?

java jpa entitymanager
Roman picture Roman · Nov 27, 2009 · Viewed 78.8k times · Source

What is the standard way to implement simple update?

Example: we have User with phone number NNNNNN and now we want to set it to YYYYYY.

@PersistenceContext
private EntityManager em;

public void update (User transientUser) {
    what should be here?
}

User entity is as simple as possible:

@Entity
@Table (name = "USER")
public class User {

    @Id
    @GeneratedValue
    private Integer id;

    @Column (nullable = false, unique = true)
    private String login;
    private String phone;

    public User () { }

    ... //some setters and getters
}

Answer

Pascal Thivent picture Pascal Thivent · Nov 27, 2009

According to the JPA specifications, EntityManager#merge() will return a reference to another object than the one passed in when the object was already loaded in the current context. So, I'd rather return the result of the merge() and write the update() method like this:

@PersistenceContext
private EntityManager em;

public User update (User transientUser) {
    return em.merge(transientUser);
}

Then, use it like this (skipping the initialization part):

user.setPhone("YYYYYY");
user = dao.update(user);

Related questions

What does EntityManager.flush do and why do I need to use it?

I have an EJB where I am saving an object to the database. In an example I have seen, once this data is saved (EntityManager.persist) there is a call to EntityManager.flush(); Why do I need to do this? …

Read More
What is the best way to update the entity in JPA

I am doing some CRUD operations using JPA. For updating an object which is the right way to do? Through update query or through the find method of EntityManager? I have one Employee object I need to update. Which is …

Read More
JPA merge vs. persist

So far, my preference has been to always use EntityManager's merge() take care of both insert and update. But I have also noticed that merge performs an additional select queries before update/insert to ensure record does not already exists …

Read More