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.
Here is my answer. Tested
When mapping your Id, switch from what I have above, which is
@Id
@Basic(optional = false)
@Column(name = "ID")
private Long id;
to
@Entity
public class Person {
@Id
@TableGenerator(name="TABLE_GEN", table="SEQUENCE_TABLE", pkColumnName="SEQ_NAME",
valueColumnName="SEQ_COUNT", pkColumnValue="PERSON_SEQ")
@GeneratedValue(strategy=GenerationType.TABLE, generator="TABLE_GEN")
private long id;
...
}
Since I use microsoft SQL server, I have to use @TableGenerator
. More information can be found here http://en.wikibooks.org/wiki/Java_Persistence/Identity_and_Sequencing#Table_sequencing
Try adding a @GeneratedValue
on your id field.
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.
@SequenceGenerator
, I use @TableGenerator with
@GeneratedValueand it works. However, will calling
flush()` every time cause performance problem, DataNucleus - Thang Pham 2012-04-06 13:05
I know it's not a persist but the merge will do the same thing more simply. I wrap my persist in an actual merge operation which will save the entity if it does not exist.
public T persist(T obj) {
EntityManager em = ThreadLocalPersistenceManager.getEntityManager();
EntityTransaction tx = em.getTransaction();
try {
tx.begin();
obj = em.merge(obj);
} finally {
if (! tx.getRollbackOnly()) {
tx.commit();
}
}
return obj;
}
/**
* This will save the object and return the id of the persisted object.
*
* @param obj
* @return The id of the persisted object.
*/
public Long save(T obj) {
persist(obj);
return obj.getId();
}