Hi,

I need to write code that would allow for dynamic specification of order-by column for a collection of children of the main object. I tried to add order to criteria object by using the collection alias:

String alias="parent.children.";

Criteria.addOrder(Order.asc(alias+"childColumn"));

But that did not sort the children inside the collection at all.

I found out that I could modify the mapping file (<set order-by="childColumn">), but this is not dynamic. In my case column name ("childColumn" here) can change at runtime.

Do I have any options for implementing this in Hibernate? I would like to do the sorting on the DB side, without writing a custom SQL/HQL query.
Any help on the subject would be appreciated.
Thanks,

Bratek

Sorry if this is a stupid question, but how are you initializing your collection in your POJO ? Hibernate recommends doing something like this:


However, this probably won't work, because the HashSet class doesn't preserve the order of its elements. You can fix this problem by using a LinkedHashSet, instead:

Hi,

I gave it a try, just to make sure, but it didn't work. I think there are a couple of issues here at play. For one, when you load objects from DB, I think Hibernate provides its own containers for Collections (those containers are lazy-load aware, etc.). Secondly, even if the Collection preserves the order, there is no guarantee that child objects will be added to Collection according to any order. Since Hibernate loads children with separate SELECT statements, I don't think that anything added to the criteria would help sorting children either. It would have to be some kind of built-in feature, like filters and the like.

Anyway, thanks for trying to help!

Bratek

Verify if this link helps you in sorting the collection.

http://www.hibernate.org/hib_docs/v3/re ... ons-sorted

Hi,

Thanks for the info. Unfortunately, in my case the search criteria is dynamic (changes between calls), so I can't put it in mapping file, since I don't know which column the collection will be sorted by.

I ran into the createFilter method before, and it looked vaguely promising, but I couldn't figure out how to use it - I'm suspecting it only works for lazy loading, since it seems to make an additional trip to the db to get the collection (and sort it). The catch is that in this example the main object (parent of the collection) must have been already loaded, otherwise where would the collection object reference come from?

Alas, I can't use lazy loading in my project. My code deals with volatile data that can change between calls, so I disabled lazy loading to make sure that I get a 'snapshot' of the data collected all at once.

Bratek