JPA Query misunderstanding

Question

I use JPA (EclipseLink). I have entity class

@Entity
@Table(name = "my_table")
public class MyEntity implements java.io.Serializable {    
  @Id
  @Column(name = "id")
  int id;    
  @Column(name = "name")
  String name;    
  @Lob
  @Column(name = "data")
  byte[] bytes;
  //getters und setters are ommited
}

And I have such query

Query query = entityManager.createQuery("SELECT m FROM MyEntity m WHERE m.name = :name");

After I get result first time, data field in database changed. But when I run this query next times I still get old value. Can anybody explain me such behavior and show me a way how to get updated value

UPD: I call query.getResultList() and get instance of MyEntity. Then other application changes data in DB and commit it (I can run sql statement and I see it's really commited). Then I call query.getResultList() again and get instance of MyEntity that contains old data. My application uses transaction isolation level TRANSACTION_READ_COMMITTED. I've checked this by

Connection c = entityManager.unwrap(Connection.class);
c.getTransactionIsolation();

UPD2: I've noticed that when I invoke the above statement entityManager.unwrap(Connection.class) the behavior is like cache cleared after this call. After this call I get updated instance by calling query.getResultList(). I'm totally confused about this.

You will need to show how the data changes and when (relative to your repeated queries), because your problem is probably related to transaction management. In other words: the change to your data probably hasn't been written to the database. — blagae, Sep 18 '14 at 14:27
I just fixed a caching problem in my app. I am pretty sure you have the same issue. Review the JPA caching - helps a lot. — Jama Djafarov, Sep 18 '14 at 14:57
Do you call first and second query from inside the same entityManager or from 2 different entityManagers? Remember of cache Level 1 that is used implicitly. — przemek hertel, Sep 18 '14 at 15:14
So unless your UPD2 has a performance hit that is significant enough to impact your project, you've likely found your solution — blagae, Sep 19 '14 at 07:15
I don't understand why this action entityManager.unwrap(Connection.class) results in clearing cache — Joel, Sep 19 '14 at 07:28
If you really want to know, go into the EclipseLink sources (you can download them if they're not available in your IDE) and then debug the EntityManagerImpl class: there is an explicit check "if (cls.equals(java.sql.Connection.class))" — blagae, Sep 19 '14 at 10:10

score 0 · Answer 1 · edited May 23 '17 at 10:33

Since there's another application changing the data, your cache is outdated. Therefore, your question is essentially a duplicate of: EntityManager doesn't see changes made in other transactions

Please try the suggestions made in the accepted answer there, and see what that does for your problem.

EDIT: clearing the cache is usually vendor-dependent, so you'll have to search for documentation for your provider. For EclipseLink, this looks promising: http://wiki.eclipse.org/EclipseLink/Examples/JPA/Caching#How_to_refresh_the_cache

EDIT2: Since you use the EntityManager, you could try this directly:

em.getEntityManagerFactory().getCache().evictAll();

Thanks, this helps. Please, read my second UPD, I'm just getting more confused — Joel, Sep 19 '14 at 07:05

score 0 · Answer 2 · answered Sep 19 '14 at 15:55

0

If you don´t want an entity to be cached you can try to mark it as not cacheable: @Cacheable(false)

@Entity
@Table(name = "my_table")
@Cacheable(false)
public class MyEntity implements java.io.Serializable {

answered Sep 19 '14 at 15:55

marcoslop

106
7

JPA Query misunderstanding

2 Answers2