Hi,
I have an entity bean with a collection of items.
| @OneToMany(cascade = { CascadeType.ALL}, fetch = FetchType.LAZY, mappedBy
="invoice")
| @BatchSize( size = 10)
| public List<Item> getItems()
| {
| return items;
| }
|
Everything works fine in everyday use. But ocassionaly I would like to perform
statistics, which is done through selecting all the entities and performing
operation on their items.
Because there is a large number of objects I have to page through them in order
to not to run out of memory. I made two attempts to solve this problems but
both are unefficient and my method timeouts.
First approach.
My query looks like:
| "select e from Example join fetch e.items where ..."
|
Then I page through the result set and make my computations on result objects:
| int resIt = 0;
| List<Example> rl = null;
| do
| {
|
| rl = q.setMaxResults(
1000).setFirstResult(resIt).getResultList();
|
| for (Example e: (List<Example>) rl)
| {
| //my code
| }
|
| resIt += rl.size();
| entityManager.clear();
|
| } while (rl.size() > 0);
|
But then I got a warning "firstResult / maxResults specified with collection
fetch ; applying in memory". I uderstand that when collection is fetched,
Hibernate cannot use sql "limit" because number of rows is not equal to number
of objects, and "in memory" means additional selects.
Second approach.
I removed join fetch from query. But then items collection are fetched ( in
batch of 10) during computatins, which is also slow. I dont want to change the
value of batch in mapping.
Do you see any solution to my problem? Maybe there is a way to temporarily
increase the batch size of the collection (for the duration of my statistics
method)?
Thanks in advance
Pawel Miniewicz
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