Deleting an entity from another entity?

[rbenko]

This might be a stupid question, but I can't seem to find the answer to it. I'm fairly new to JBoss/Hibernate/EJB3.0, but I have a good deal of experience using TopLink. I have a collection of entity objects contained in another entity object. When I remove an entity from the collection (via a method on the owning entity) I would like to remove it from the datastore - how do I go about it? Do I need to get a handle to the EntityManager and call remove()? If so, what is the best way to get a handle to the EntityManager inside an Entity Bean?

TopLink has a setting called 'Private Owned', which would automatically delete an object if you removed it from the owning entity's collection. I see that Hibernate does this for simple collections (Strings and the like), but not for Entity collections. Thanks for any help.

[jacekolszak]

Hmm... maybe you should addnotate the collection with Cascade.REMOVE ?

For example:

public class Container {
private List<Item> items;

@OneToMany(cascade=CascadeType.REMOVE)
public List<Item> getItems();
}

When you remove an item from the list, you removed the entity from the datastore too.

getItems().remove(0);
em.merge(container);

I think it should work, but not sure for 100%.

[rbenko]

Thanks for the reply. Collection is already annotated with Cascade.REMOVE - merge() doesn't work in this instance. I think I need a way to get to the EntityManager inside my Entity Bean. For example:

@Entity
public class Container {
 private List<Item> items;

 @OneToMany(mappedBy="security", cascade=CascadeType.ALL)
 @MapKey (name="key")
 public Map<String, SecProperty>getProperties();

 ...

 public void removeProperty(String key) {
 if (getProperties().containsKey(key)) {
 Object obj = getMyProperties().remove(key);
 //
 // This is where I think I could use the EntityManager
 // to delete from database:
 //
 em.remove(obj);
 }
 }
}

What is the best way to inject the EntityManager into an Entity Bean? Or is there is another way to accomplish this without using the EntityManager?

[rbenko]

Okay - more searching led to a 'workaround' using Hibernate's native CascadeTyp.DELETE_ORPHAN setting. I'm not quite sure why a facility like this or like TopLink's 'Private Owned' flag is left out of the EJB spec - it seems like a fairly common mechanism.