Many-to-one associated entities save problem

Darbic · **Posted:** Sat Jan 13, 2007 2:13 pm

Hi, please help with the following issue.

I have two entities:

Code:

@Entity
@Table(name="SHOPPING_SESSIONS")
public class ShoppingSession {
  ...
  @ManyToOne(cascade={CascadeType.PERSIST, CascadeType.MERGE}, fetch=FetchType.LAZY)
  @JoinColumn(name="WEB_SESSION_ID", nullable=false)
  private WebSession webSession;
  ...
}

@Entity
@Table(name="WEB_SESSIONS")
public class WebSession {
  @Id
  @Column(name="WEB_SESSION_ID", updatable=false)
  private String id;
  ...
  @OneToMany(mappedBy="webSession" cascade=CascadeType.REFRESH, fetch=FetchType.LAZY)
  @JoinColumn(name="WEB_SESSION_ID")
  private Set<ShoppingSession> shoppingSessions;
  ...
}

Now, this is typical code performed when new shopping cart is created in eshop (unlimited shopping session may be created in one web session):

Code:

ShoppingSession shoppingSession = new ShoppingSession();
if (webSession == null) {
  webSession = new WebSession();
  webSession.setId(request.getSession().getId());
}
shoppingSession.setWebSession(webSession);

When shopping cart is being saved the persist() method is called for save ShoppingSession to the DB. Hibernate calls INSERT on both SHOPPING_SESSIONS and WEB_SESSIONS tables.

Now, the new shopping cart (ShoppingSession entity) is created in the same web session and the first above code is perfomed again. In this time the once saved WebSession is set to the newlly created ShoppingSession. When I try to save the new ShoppingSession, Hibernate calls INSERT on WEB_SESSIONS again. This call fails because unique WEB_SESSION_ID constraint.

Please help me with this situation and advice correct solution.

Thank you very much.

mmrath · **Joined:** Mon Jan 15, 2007 3:53 am **Posts:** 2

I am facing the same problem. This can be done in the following way

Code:

ShoppingSession shoppingSession = new ShoppingSession(); 
 if (webSession == null) { 
  // If WebSession with id already exists get that 
  // Else create a new one.
} 
shoppingSession.setWebSession(webSession); 

Darbic · **Posted:** Mon Jan 15, 2007 7:55 am

Thank you. A similar solution I used too. But now, I know a matter of this issue. It is very important thing when using Hibernate with Spring framework.

In Hibernate, the above situation becames when the entity changes state to detached between the both persist() callings. I couldn't enter why this happens in my application. Now I know why thanks to my friend Milan Cecrdle. In my Spring web application I'am using the OpenSessionInViewFilter filter. It ensures that all persistent entities changes their state to detached after rendering a view.
Milan, thank you for explanation.

mmrath · **Joined:** Mon Jan 15, 2007 3:53 am **Posts:** 2

Can u please tell me the solution.

Darbic · **Posted:** Thu Jan 18, 2007 8:36 am

Solution 1
You can break association in domain objects and store only webSessionId (instead reference to webSession object) in the ShoppingSession. Then you must manage WebSession and ShoppingSession separately.

Solution 2
Before saving new shoppingSession (with reference to already stored webSession) you must call the merge() on webSession object what changes its state to persistent.