delete object from collection

Maciekj · **Posted:** Fri Sep 02, 2005 5:01 pm

Hi
I'm working with ejb 3.0 (jboss 4.0.3 rc2).

I have two classess:

Code:

@Entity
@Table(name="parents")
public class Parent implements Serializable {
   private Integer idparent;
   private String name;
   private List<Child> children;
   
   @Id(generate=GeneratorType.AUTO)
   @Column(name="idparent")
   public Integer getIdparent() {
      return idparent;
   }
   public void setIdparent(Integer idparent) {
      this.idparent = idparent;
   }
   
   @Column(name="name")
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
   
   @OneToMany(mappedBy="parent", fetch=FetchType.EAGER)
   public List<Child> getChildren() {
      return children;
   }
   public void setChildren(List<Child> children) {
      this.children = children;
   }
}

Code:

@Entity
@Table(name="children")
public class Child implements Serializable {
   private Integer idchild;
   private String name;
   private Parent parent;
   
   @Id(generate=GeneratorType.AUTO)
   @Column(name="idchild")
   public Integer getIdchild() {
      return idchild;
   }
   public void setIdchild(Integer idchild) {
      this.idchild = idchild;
   }
   
   @Column(name="name")
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
   
   @ManyToOne
   @JoinColumn(name="parent")
   public Parent getParent() {
      return parent;
   }
   public void setParent(Parent parent) {
      this.parent = parent;
   }   
}

I have stateless session bean which contains methods:

Code:

public void updateParent(Parent p) {
  em.merge(p);      // entity manager
}
public List<Parent> getParents() {
  return em.createQuery("from Parent p").getResultList();
}

in my client application there is something like this:

Code:

Context context = new InitialContext();
Information inf = (Information)context.lookup(Information.class.getName());
Parent p = inf.getParents().iterator().next();         
Child c = p.getChildren().iterator().next();
p.getChildren().remove(c);
c.setParent(null);
inf.updateParent(p);

In my opinion it should be OK, but this code doesn't delete anything in DB.
Adding new objects works good.
I was trying cascade (ALL and ORPHAN-DELETE) but i had the same problem.

What should I fix? How to delete object from collection?

Sorry for my english!!

emmanuel · **Posted:** Sat Sep 03, 2005 8:30 am

as is this stuff can't work because, Hibernate has no notion of the removed children since you pass it =back the parent object (wo link to the removed children anymore)

The solution is cascade delete orphan in the @OneToMany

Maciekj · **Posted:** Sat Sep 03, 2005 4:50 pm

Hi,
thanks for your reply.

this is my code: (using delete-orphan)

Code:

@OneToMany(mappedBy="parent", fetch=FetchType.EAGER)
@org.hibernate.annotations.Cascade({CascadeType.ALL, CascadeType.DELETE_ORPHAN})
   public List<Child> getChildren() {
      return children;
   }
   public void setChildren(List<Child> children) {
      this.children = children;
   }
}

And my client code:

Code:

Parent p = inf.getParents().iterator().next();
Child c = p.getChildren().iterator().next();
c.setParent(null)
p.getChildren().remove(c);
inf.updateParent(p);

It still doesn't work properly. On output (show_sql="true") hibernate writes only [STDOUT] Hibernate: select (...)
How to implement it?

Cheers.

emmanuel · **Posted:** Sat Sep 03, 2005 5:34 pm

Check the unit test suite, there is a testCascadeDeleteOrphan() method (see link)
http://cvs.sourceforge.net/viewcvs.py/hibernate/HibernateExt/metadata/src/test/org/hibernate/test/annotations/onetomany/OneToManyTest.java?rev=1.10&view=auto

Maciekj · **Posted:** Sat Sep 03, 2005 7:12 pm

Thanks for reply, and very good link!
but...
It still doesn't work :/

Code:

Troop disney = new Troop();
disney.setName("Disney");
Soldier mickey = new Soldier();
mickey.setName("Mickey");
disney.addSoldier(mickey);
s.persist(disney);

It is such like piece of my code:

Code:

Parent p = new Parent();
p.setName("Krystyna");
Child c = new Child();
c.setName("Andrzej");
p.addChild(c);
inf.saveParent(p);       // stateless session bean where is em.persist(p);

It works good, but... (code from session bean)

Code:

Parent p = em.find(Parent.class, new Integer(9));
Child c = p.getChildren().iterator().next();
p.getChildren().remove(c);
em.merge(p);

It doesn't delete anything, but in my opinion it is quite like:

Code:

Troop troop = (Troop) s.get( Troop.class, disney.getId() );
Soldier soldier = (Soldier) troop.getSoldiers().iterator().next();
troop.getSoldiers().remove(soldier);

I have the same annotations like in Tropp, and Soldier classess.
Any ideas?

greet

morgab · **Joined:** Tue Sep 06, 2005 3:34 am **Posts:** 3

I was seeing this error too, however I found when I removed the cascade attribute completly then it started working fine. I need to test this further but my impression is that the children are being removed and updated properly.

My mappings and code were very similar to the above postings.

morgab · **Joined:** Tue Sep 06, 2005 3:34 am **Posts:** 3

My above posting was incorrect, without the cascade the child objects are not persisted, which is what I expected to happen. I have noticed from the Logs that delete orphans is being called on the collection, however no orphan objects are being found, the log entry looks like this:

Quote:

DEBUG main org.hibernate.engine.Cascades - deleting orphans for collection: -------

DEBUG main org.hibernate.engine.Cascades - done deleting orphans for collection: --------

This implies to me that the parent-child relationship is not setup properly or that there is a hanging reference to the child object that is stopping it from being considered an orphan. Please advise if you have any suggestions for the mapping.

Maciekj · **Posted:** Tue Sep 06, 2005 7:28 pm

Hi

Thanks for reply

I decided to change mappings, and now I have something like this:

Code:

@OneToMany(fetch=FetchType.EAGER,cascade=javax.persistence.CascadeType.ALL)
@org.hibernate.annotations.Cascade(org.hibernate.annotations.CascadeType.DELETE_ORPHAN)
@JoinTable(table=@Table(name="parents_children"),
        joinColumns=@JoinColumn(name="idparent"),
        inverseJoinColumns=@JoinColumn(name="idchild"))
public List<Child> getChildren() {
    return children;
}
    
public void setChildren(List<Child> children){
    this.children = children
}

Code:

@ManyToOne
@JoinColumn(name="parent")
public Parent getParent() {
  return dzialprzemyslu;
}
public void setParent(Parent parent) {
this.parent = parent
}

It works properly, but how to make it without creating join table? (parents_children)

Do you have any ideas?

greet

morgab · **Joined:** Tue Sep 06, 2005 3:34 am **Posts:** 3

I found that my error was that I was not calling Commit and Close after doing my create. Once I added code to Commit and Close after the create of the parent then retrieved the object and removed the orphans it worked fine. Psuedo code for what I did is as follows:

Code:

Create Parent
Commit and Close
Retrieve Parent
Orphan Children
Commit and Close

From my understanding of Hibernate I am guessing that it would have seen the non commited orphaned children as 'dirty' records rather than 'orphaned' records.

Maciekj · **Posted:** Thu Sep 08, 2005 4:46 am

Hi

Is there any way to do it with container-managed EntityManager?
I can't close session...