Deleting objects from a collection

danieltaylor.nz · **Joined:** Wed Feb 15, 2012 12:11 am **Posts:** 2

I would like to ask for your help on a hibernate question.

We have a system where we load an object from our relational database and serialize it into JSON.
Our Class looks like this:

Code:

@Entity
@Table(name = "mytable")
public class MyClass implements Serializable {
    @Id
    @NotNull
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id = 0L;

    @OneToMany(fetch=FetchType.EAGER)
    @JoinColumn(name = "parent_id", updatable = false)
    private List<ChildObject>  collection = new ArrayList<ChildObject>();
}

The object serialized into json might look a little like:

Code:

{
    "id" :"12",
    "collection": [
        {
            "id": 1,
            "parent_id": "12"
        },
        {
            "id": 2,
            "parent_id": "12"
        }
    ]
}

We modify the json in the client, and then send it back to the server. The json gets deserialized back into an object, and the database is updated via hibernate.

Code:

MyClass myObject = new JSONDeserializer< MyClass >().deserializeInto(json, new  MyClass());

sessionFactory.getCurrentSession().update(myObject);

This works fine when updating properties, and adding objects to the collection. My only problem comes when I want to remove an object from the collection, and have it deleted from my database. I have looked for the solution to this everywhere and have tried many variations on Cascade annotations and the deleteOrphan = true annotation without success.

I recieve the following JSON from the client, and notice that the client has removed the first element in the collection:

Code:

{
    "id" :"12",
    "collection": [
        {
            "id": 2,
            "parent_id": "12"
        }
    ]
}

I deserialize the json back into my object and update via hibernate. The missing element is ignored, and remains in the database.

Code:

MyClass myObject = new JSONDeserializer< MyClass >().deserializeInto(json, new  MyClass());

sessionFactory.getCurrentSession().update(myObject);

Perhaps I am going about this the wrong way, can someone please help me out.

Many thanks,

Dan

danieltaylor.nz · **Joined:** Wed Feb 15, 2012 12:11 am **Posts:** 2

If anyone else was stuck on this, it turns out the issue was not the hibernate annotations, but the method for persisting the data.

With the following annotation:

Code:

    @OneToMany(fetch=FetchType.EAGER, orphanRemoval = true)
    @JoinColumn(name = "parent_id", updatable = false)
    private List<ChildObject>  collection = new ArrayList<ChildObject>();

I changed the following line:

Code:

sessionFactory.getCurrentSession().update(myObject);

to

Code:

sessionFactory.getCurrentSession().merge(myObject);

And it worked fine.

Here is a post by someone with the same issue and a discussion on the difference between update() and merge()
viewtopic.php?f=1&t=987543

strjames · **Joined:** Fri Feb 17, 2012 8:20 am **Posts:** 18

Yeah i too agree....

Difference Between Merge And Update Methods In Hibernate

xiaotuanzi · **Joined:** Tue Feb 21, 2012 12:57 am **Posts:** 5

I also agree.