Many-to-many deletes wrong relationship rows upon save

djzeel · **Posted:** Wed Feb 01, 2006 9:15 pm

Dear Hibernate Gurus!

I am migrating a code that worked with XDoclet tags (and HBM file) to annotations, and I am running into a problem with many-to-many relationship.

I have A mapped to B as a unidirectional many-to-many, with a relationiship table AB (A_id, B_id), and A being the owning (and only) side of this relationship. Save of A should cascade save of B and the relationship.

Code:

  
  a1 = new A();
  a1.addB(new B());
  a1.addB(new B());
  session.save(a1);

This correctly saves two Bs, and two rows in AB table, and row in A table (A1).

Now, I fetch A1 and reset it's ID to null (thus converting it into a 'new' instance), which is still linked to the set of Bs. What I want is to save this modified A (with null ID), linking it with the same set of B rows, without affecting relationship between A1 and B.

This works when mapped as follows using XDoclet/XML, but when mapped using annotations (see below), the relationship rows for A1 get deleted when I save (what now should be) A2. It almost looks like the sets that were fetched for A1 were "tagged" with A1, so when the same sets are found to be linked to another instance A2, hibernate decides to delete them.

Here is a summary of what happens:

Start with this:

Code:

 A1 ->  A1_id, B1_id -> B1
    ->  A1_id, B2_id -> B2

Here is what I want to see after I fetch A1 and call A1.setId(null) and then save it:

Code:

 A1 ->  A1_id, B1_id -> B1
    ->  A1_id, B2_id -> B2
 A2 ->  A2_id, B1_id -> B1
    ->  A2_id, B2_id -> B2

Instead, with annotations, i am seeing this:

Code:

 A1  
 A2 ->  A2_id, B1_id -> B1
    ->  A2_id, B2_id -> B2

Here is XML mapping code that works this way:

Code:

 ... mapping for A ...

       <set
           name="B"
           table="AB"
           lazy="false"
           cascade="save-update"
           sort="unsorted"
           access="property" >

           <key column="A_id"/>

           <many-to-many
               class="B"
               column="B_id"
               outer-join="auto"
            />
       </set>

And here is the broken annotations mapping:

Code:

@javax.persistence.Entity(access = AccessType.FIELD)
@Table(name = "A")
@org.hibernate.annotations.Proxy(lazy = false)

class A {

    @ManyToMany(
        targetEntity = B.class,
        cascade = {},
        fetch = FetchType.EAGER)
    @JoinTable(
        table = @Table(name = "AB"),
        joinColumns = {@JoinColumn(name = "A_id")},
        inverseJoinColumns = {@JoinColumn(name = "B_id")})
    @org.hibernate.annotations.Cascade(
        {org.hibernate.annotations.CascadeType.SAVE_UPDATE})
    private Set<B> networkPorts = new HashSet<B>();

Is there any way to prevent Hibernate from EVER deleting from my relationship table? My classes are essentially immutable, and the reason I need to do the above, is to save a new version of the object... If I could somehow tell hibernate that the many-to-many should never be deleted...

Anyone?

Thank you in advanace,
Zeel.

djzeel · **Posted:** Thu Feb 02, 2006 3:34 pm

I think I may know what's going on.... The old XDoclet code used "property" access type on the setters for the relationship, and did this:

Code:

  public void setBs(Set bs) {
     this.bs = new HashSet(bs);
  }

What I think this did, is replace Hibernate's set with HashSet. I suspect that Hibernate's set implementation holds on to the IDs of the entity it was originally from.. Replacing the set with HashSet clears this information, and so the rows do not get deleted.

I am going to try to upgrade to beta8 so that I can override access type on a per property level and see if that helps...

emmanuel · **Posted:** Wed Feb 08, 2006 1:25 pm

your assumptions were rights.
The @AccessType should solve your problem

djzeel · **Posted:** Wed Feb 08, 2006 2:43 pm

emmanuel wrote:

your assumptions were rights.
The @AccessType should solve your problem

Indeed overriding @AccessType on my collections fixed the issue.

Thanks,
Zeel.