Is there a way in Hibernate to represent the behavior of a LinkedHashSet?

I have the following situation:
An instance of Class A contains a Set of instances of Class B, but the set must be arbitrarily ordered by the user (i.e: it is not "sorted", but "ordered").
So, I need a mix of List and Set, which is precisely what LinkedHashSet gives.

My DB table to represent the association looks like:

Please note:
- ORDER column is not represented in either of the two original classes (A and B) since the usage of a LinkedHashSet in A is representative enough.
- There is a Unique constraint on (CLASS_A_ID, CLASS_B_ID), and this is correct since it is a Set: I don't want users to post twice the same B object.

Now, here is the thing:

* If I use a Set, then I will not be able to represent ORDER column.
* If I use a List (and set index column to ORDER) then Hibernate fails to update the table because it breaks the Unique Key (since it relies on non-uniqueness of the List - other posts in the forum talk about that).

What should I do? I know I can create another association class to store this but I really would like to have this issue solved by the persistence framework instead.

Are you try make equals method and user simple List

regrads

I'm not sure if that'll work. I am currently using a List, and my equals method is defined correctly in class B, the problem is that when I remove an item from the list, and it's not the last one, Hibernate generates a constraint error when updating the table.

Here is an example:

Suppose that I remove B1 from the list (order 0), then the table should end up having B3 in order 0 and B2 in order 1.
Hibernate performs the following steps:
1) DELETE row with order 2
2) UPDATE row with order 0 to refer to B3
3) UPDATE row with order 1 to refer to B2

The problem is that in step (2) the unique key constraint is violated (because both row with order 0 and that with order 1 refer to B3 in that particular point in time).

You may refer to http://forum.hibernate.org/viewtopic.php?t=932149 for a discussion on this issue.

This is because Hibernate assumes that the list does not contain unique items (i.e: It is not a Set). I am Ok with that, but then using a List does not work for me (unless of course I remove all items and re-add all of them every time I want to delete a single item, but I'd rather search for other alternatives first).

Is there any other way around that I could use to solve my problem?

Hi ,

I am facing exact same problem . Is there any collections supported by hibernate for this purpose ?

Regards,
lalrow