hi there!
I've been searching for ways to optmize my HQL queries. I was able to reduce the number of selects with the "left join fetch", but not like in the examples I found. They [the examples] shows the query in the form "select <columns> from <table> where <condition> left join fetch <relation>", but always I did like this I got the syntax error , now my queries are like "from <table> left join fetch <relation> where condition>" - I wander if the two forms are equivalent.

tutorial site: http://www.javalobby.org/articles/hiber ... e=archives

Now I want to reduce the number of columns retrivied with the "select new" type of query. But I've some doubts I haven't been able to elucidate.

1) The queries are based on DAO's classes - what I would like to do is instantiate the constructors on the concrete classes - the POJO's - of course, remebering of the empty constructor Hibernate needs to creat the objects, - there is a way to do this or I need to create new (simple - just the fields that representing the columns I need) POJO's and new DAO's classes? or just the creation of a POJO is enough?

2)How a reference the class in the constructor on the HQL string query? I use the getClassName followed by an alias to reference the class in my string queries - so it would by like "select <alias>(<alias>.field1,...,<alias>.fieldn) from getClassName() <alias>"?

3) Can I create as many constructor as I need in the same class to use in the HQL query? Or do I really need to create a class for each constructor used in the query? This sucks, besides, i will loose on efficiency - There are any paper comparing the efficiency of the various form of querying?
Thanks for all.

You can specify as many constructors as you wish. Hibernate uses the default constructor for basic use, and whatever constructor fits the query for the others.



I think there is an issue preventing the use of Collections in the constructor. So you couldn't do something like



In this case, I believe you would have to do


But I haven't tried this in a few months so it might have been added. Or I could just be remembering it wrong.

ok - but i have to mapping the MyObject class?

Nope, the MyObject class doesn't have to be mapped, you just need the required constructors.

sorry, I forgot to say, I've been using the spring framework with hibernate - thats why i think the MyObject class need to be maped, cos' I've tried it before, and I get "no class found" exception triggered by spring.

That sounds like a classpath issue rather than a mapping issue to me, but then again I've never used Spring.

it was a path mistake, I forgot to inform the path of the package of MyObject class. This solution is very straightforward for me, that have to optmize the whole HQL queries, since the system is ready, I don't need to do big changes in its code.

I was wandering - Isn't enough setting hibernate.use_outer_join to true the same as using left join fetch?Cos "left join fetch" is as good as "select new" in some circustances.

Hello!

Could you tell me how you solved your problem?
Indeed, I'm working under Eclipse and I created my object in a new package but in the source folder src.

I have the following exception net.sf.hibernate.QueryException: class not found and I don't know what to do...

hi there!!!
It was needed to write the whole path ( package way) that the class is into.
( yes, I finished a sentence with a preposition :P )
something like:

select new br.srv.dao.concreteclass.MyObject(....) from ....

Hello!

Ok I understood now!

Thankx a lot, it works!

If you are Portuguese (because of your name) , I would say "Obrigado!", otherwise "Thank You!" :D

de nada :)