THE way to delete child objects using JPA + Hibernate

gunderr · **Joined:** Tue Feb 03, 2009 11:23 am **Posts:** 4

Hi

I've been fighting with how to delete child objects in a OneToMany all day. At first I didnt realise that JPA does not (yet) support delete-orphan, so although the link between my parent and child(ren) was being severed, the child was still in the Database.

Then I ran into all sorts of concurrent modification issues because I was using my collection in a for(Child c: children).... loop, and of course, calling children.remove(c) in this case will cause that problem.

So, based on the other posts I've read, I think I have the solution, which is shown below in case it's helpful to other people who are beginners like me

Code:

        FileType fileType = findFileType(fileTypeId);
        Iterator it = fileType.getFields().iterator();
        while(it.hasNext()) {
            Field f = (Field)it.next();
            if(fieldIds.contains(f.getFieldId())) {
                it.remove();
                entityManager.remove(f);  // this bit required because JPA doesnt support delete-orphan
            }            
        }

Here's my mapping btw - it uses the default cascade behaviour (ALL) and uses a join table

Code:

@OneToMany(fetch=FetchType.LAZY)
    @JoinTable(
            name="FILE_TYPE_FIELD",
            joinColumns = @JoinColumn(name="FILE_TYPE_ID", referencedColumnName="FILE_TYPE_ID"),
            inverseJoinColumns = @JoinColumn(name="FILE_FIELD_ID", referencedColumnName="FILE_FIELD_ID")
    )

What I would really appreciate is if someone could just say yeah (or no), this is the standard way of doing things, because I struggled a bit finding good examples, and I am going to be writing a whole load of these soon so I want to do them right :)

Also, for bonus points, the docs recommend using a join table, even though a simple foreign key would suffice. Why is this?

Thanks

mmerder · **Posted:** Wed Feb 04, 2009 12:47 pm

Was it not possible for you to use
@org.hibernate.annotations.Cascade(CascadeType.DELETE_ORPHAN) or do you want to use JPA-Annotations only?

gunderr · **Joined:** Tue Feb 03, 2009 11:23 am **Posts:** 4

Hmm, yeah that works. I did try it earlier but because I was tying myself in knots because of the loop issue, I took it out again.

So, changing the mapping to the following works (as long as I also add CascadeType=ALL)

@OneToMany(fetch=FetchType.LAZY, cascade=CascadeType.ALL)
@org.hibernate.annotations.Cascade(org.hibernate.annotations.CascadeType.DELETE_ORPHAN)
@JoinTable(
name="BULK_UPLOAD_FILE_TYPE_FIELD",
joinColumns = @JoinColumn(name="BULK_UPLOAD_FILE_TYPE_ID", referencedColumnName="BULK_UPLOAD_FILE_TYPE_ID"),
inverseJoinColumns = @JoinColumn(name="BULK_UPLOAD_FILE_FIELD_ID", referencedColumnName="BULK_UPLOAD_FILE_FIELD_ID")
)

I don't mind using the Hibernate-specific annotations since the problem is JPA limitation.

Thanks

angeldude · **Posted:** Thu Feb 05, 2009 11:42 am

I've recently find out that by using Hibernate mapping:

org.hibernate.annotations.CascadeType.DELETE_ORPHAN

changes the fetching type to LAIZY.

So if you have something like:

@OneToMany(fetch=FetchType.DELETE_ORPHAN, cascade=CascadeType.ALL)
@org.hibernate.annotations.Cascade(org.hibernate.annotations.CascadeType.DELETE_ORPHAN)

and you modify an entity like:

main entity with 2 children entities

by removing one child, when you merge the changes the fetch goes to LAIZY.

Hope this helps.

P.S.
I'm still struggling to find a solution on moving fetch=EAGER again as I don't want to manually remove orphan children just for using JPA annotation sake. So if anyone has an idea then please document it.