Which collection type for sorted collection?

wpfeiffe · **Posted:** Fri Mar 26, 2004 2:34 pm

A colleague and I are going round and round on trying to figure out which Hibernate collection type will best fit our need for an ordered collection that does NOT have a good candidate column for an index. We have several scenarios where the collections in question use either dates or strings or large integer numbers (abstract keys) to determine their collections's ordering.

Which of the Hibernate collection types (List, Set, Map, Bag) best fit the need for a collection that will return a guaranteed order on interation over the collection?

I have currently settled on using a set with an order-by tag to set the order. I'm not sure that this will guarantee the order of iteration however. My colleague is suggesting that a Bag will maintain order without the need for an explicit "hibernate" index tag.

Can someone clarify this?

Thanks for any help. Using Hibernate 2.1.2 on Oracle 9.2.

gavin · **Posted:** Fri Mar 26, 2004 3:49 pm

Quote:

I'm not sure that this will guarantee the order of iteration however.

What do you mean by this??

wpfeiffe · **Posted:** Sat Mar 27, 2004 5:36 pm

gavin wrote:

What do you mean by this??

I'm not sure that a Set will guarantee a specified order when using the iterator returned from a Hibernate created Set, even though I've specified an "order-by" tag in hibernate.

Overall my general question is what hibernate collection type is the best fit for a list of ordered objects that don't have a good candidate "index" column as required by the Hibernate List type.

Sorry if I'm not being clear but I'm still learning the Hibernate ins and outs.

Thanks for any help

wpfeiffe · **Posted:** Tue Mar 30, 2004 12:01 am

Section 6.6, 6.7 of the reference answered my question.

pvradhakrishna · **Joined:** Tue Feb 19, 2008 6:05 pm **Posts:** 82

Code:

                
                <set name="children" order-by="child_id desc" cascade="none" inverse="true">
         <key column="parent_id" ></key>
         <one-to-many class="Child"/>
      </set>

           private Set<Child> children = new TreeSet<Child>();

A query

Code:

from Parent parent left join fetch parent.children

brings the children in the right order

Interestingly, without the Child object being implementing comparable or any thing I am able to get the set in the correct order I wanted.

After testing many times, but how is this possible and why am I getting the set in the right order I wanted from a set???

I know that I just cannot add to a TreeSet without the class implementing comparable but not only am I able to add to my TreeSet but also get the set elements in the right order??

Code:

select parent.parent_id, child.child_id from Parent left join children child 
order by child_id asc

also brings the children in ascending order