JPA: How to get Id after persist in standalone java app

Question

This is a standalone java application, not web application. So when I persist the object like this

public <T> T create(T t) {
    em.getTransaction().begin();
    em.persist(t);
    em.flush();
    em.getTransaction().commit();
    return t;
}

The id inside the T t object is still null, even though a new row with correct data and id is created correctly inside the database. Usually in my web app that utilize @EJB, the id available right after I persist, since it persist the entity object into my persistence context, I am not sure if I have my persistence context here?

This is how I mapped my id inside my @Entity Class

@Id
@Basic(optional = false)
@Column(name = "ID")
private Long id;

also I make the id of this table in the database AUTO_INCREMENT, like this

CREATE TABLE Config
(
    ID int NOT NULL AUTO_INCREMENT,
    PRIMARY KEY (ID)
)

This is how I obtain my EntityManager

EntityManagerFactory emf = Persistence.createEntityManagerFactory("CorePU");
em = emf.createEntityManager();

Here is what inside my persistence.xml

<persistence-unit name="CorePU" transaction-type="RESOURCE_LOCAL">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>    
<class>com.wf.docsys.core.model.Config</class>    
<properties>
  <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/XNINFODB"/>
  <property name="javax.persistence.jdbc.password" value="xxx"/>
  <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
  <property name="javax.persistence.jdbc.user" value="xxx"/>
</properties>

Please help, I am not sure what I did wrong here.

Answer 1

Try adding a @GeneratedValue on your id field.

Answer 2

As I found on this post the EntityManager have a method called refresh that will update your object after you persist him.

So your code will probably looks like this:

public <T> T create(T t) {
    em.getTransaction().begin();
    em.persist(t);
    em.refresh(t);
    em.flush();
    em.getTransaction().commit();
    return t;
}

I haven't tested this, so I'm not sure where exactly to put the refresh method call, there, after the commit, after the flush, etc.

Hope it can help you.

Good luck.