does anybody know how i can fetch only part of the information in hql
in the following scenario:

class A has a collection of class B.

class A
{
Collection<B> bees;
}

and i want to check an equality on the "bees" part.

something like the following:

================

function: isEqual
-------------------
A a1;
A a2;

if(a1.bees.size() != a2.bees.size())
return false;

Iterator<B> b1 = a1.getBees();
Iterator<B> b2 = a2.getBees();
while(b1.hasNext())
{
if(b1.next().getId() != b2.next().getId())
return false;
}

return true;

==========================


and the HQL is something like the followings:

select a from A a where a.id=8

- i dont want to fetch all the "bees" part in the HQL.
B is very big one (even when i get only the primitive part)
- i just want to compare the ids.
- the "size()" part also causes for lazy loading.
- comment: the id will always exist in the equal function.


thanks.

I am a little lost here. what do you want the HQL do for you? get two As and tell you whether they have the same B collections?


Farzad-

i want the HQL return all the ids of the "bees",
so no additional query will be when i perform the following:
b1.next().getId() != b2.next().getId()

The bees part is "lazy".

i also dont want all the bees data to return in the query.


and of course the "size()" part will not fetch also the "bees" data.
i dont need it.

The only thing that comes across my mind is that you force fetching the collection by doing a fetch join as shown below:



and for B you set all the attributes except the identifier to be lazy loaded. Therefore, when that query runs it loads the collection but only the ids for bees and it all executes in one query. Note you will have to instrument your compiled code so that property lazy loading works. Refer to "19.1.7. Using lazy property fetching" of hibernate document if you need more information on property lazy loading.


Farzad-

Wouldn't the "extra-lazy" fetching strategy be helpfull in this instance?
I'm not sure, but it might be usefull to check out the Primer On Fetching Strategies for details on the subject.

thanks !

is there a way to fetch something in HQL with "extra data" on some field,
like i can do with "eager" (and the field is mapped as "lazy") ?