Hi,

I have the problem of ordering a set using a property defined in a joined class (Hibernate 2.1.3).


I'd like to retrieve Groups with their Items ordered by the Type's Description, specifying this in the mapping files.

I'd like to avoid to specify a sort attribute and a comparator for the items, to save CPU cycles (items can be numerous, order of 10,000), and also because the comparator must compare the whole item state, not only the field I'd like to use for ordering (otherwise calling add() to the set will behave strangely).

I have searched this forum and google, but I could not find any solution for this.
Is it possible to tell hibernate to order the items like described ? Or it is a missing feature ? Or am I going the wrong way ?
Has anyone had this problem before, solved it and willing to share the solution ?

Something on the lines of this, maybe ?



Thanks in advance,

Simon

I have the same problem.
If anyone one can point the right direction.....

Tks
Felipe

You can specify to sort a set using a comparator class - see the sort attribute shown at http://www.hibernate.org/hib_docs/reference/en/html/collections.html#collections-mapping.

Sorry, I really should stop posting when I'm tired.

If you want to avoid using a comparator, then you can use the order-by attribute, where you specify the columns to order by. Since your item-type will be pulled out in the same query as your item, through a join, you should be able to specify that your items sort by their item-type description.

Hi sdknott,

thanks for the suggestion; but AFAIK, order-by takes a SQL expression that refers to a column of the table where Items are stored, where instead I need a column of the table where Types are stored.

Regards,

Simon

Hmm, so it seems! I assumed you could order-by on the joined table columns as well, but it seems not.

You might want to have a look at using filters at the bottom of the sorting section on file://localhost/C:/code/java/osource/hibernate-2.1/doc/reference/en/html/collections.html#collections-sorted. If you lazily load your collection and then use a filter, it might give you what you're after.

Hmm try this URL which doesn't point to my local harddisk :)

http://www.hibernate.org/hib_docs/reference/en/html/collections.html#collections-sorted

Hi sdknott,

Yes, I have read that section. My understanding is that it returns a new sorted set, but it does not order the one in the object graph.



After this, group.getItems() is still unordered, isn't it ?

Simon

I am still clueless on this issue, so should I open a JIRA request for enhancement ?

Or is it possible to achieve it in Hibernate already ?

Thanks

Its possible; use a query or a filter.

I also have as a TODO: "enhance order-by to support embedded subselects"

Am I correct in saying that the filter will create an ordered copy and leave unordered the set attached to the main object ?

And that using the Query API I should put the order-by clause in the HQL statement ?

I hoped it was possible to specify the ordering in the mapping, like it is possible now with the order-by attribute.



Okay, so I won't file a JIRA item.

Thanks for your time Gavin.