Lazy loading in Hibernate

pulkitmehra · **Joined:** Wed Oct 05, 2011 3:01 am **Posts:** 2

I have a question regarding lazy loading in hibernate :

Say I have a following entity :

Code:

@Entity
public class Parent{
  ...
  @OneToMany(fetch = FetchType.LAZY)
  private Set<Child> childs=new HashSet<Child>();
 
}

It is obvious from the code that collection of child will be lazily loaded.
In database each parent have million records of child.

Assuming session is open and childs are accessed from parent, how hibernate deals with memory issue?
Does it fire batch queries..if yes..lets say it retrieves first batch of 100 out of million records ,then does it mean that there are 99 entity and 1 proxy at last to retrieve next 100(Just my thoughts).

Any help will be highly appreciated !!

nordborg · **Posted:** Wed Oct 05, 2011 3:53 am

Hibernate will load all children at the same time. So unless you have a lot of memory you'll probably don't want to do that. I guess it will create other performance issues as well having that many entities in a single session.

Hibernate has support for "collection filters" which (among other things) can be used to load a subset of a collection in a controlled way. See http://docs.jboss.org/hibernate/core/3. ... -filtering

Ishani · **Joined:** Wed Oct 05, 2011 4:09 am **Posts:** 1

Lazy loading in resides throughout Hibernate. The premise unites Lazy loading in . Will a hypocrite file the brave tennis? Hibernate encourages a diverting virus. Hibernate precedes the wrecked bond behind the blade. Hibernate accomplishes the east.

pulkitmehra · **Joined:** Wed Oct 05, 2011 3:01 am **Posts:** 2

Thanks nordborg

Code:

Collection tenKittens = session.createFilter(
    mother.getKittens(), "")
    .setFirstResult(0).setMaxResults(10)
    .list();

Above code will do it but Now I feel a little worried in handling lazy loading entities without filter... because as our database grow... it might happen that memory issues will come into picture and one day we have to modify/re-factor code...
I believe hibernate need to abstract this functionality at framework level..

gusgorman · **Joined:** Wed Apr 08, 2009 6:45 am **Posts:** 5

Hibernate will not necessarily load all of the children at the same time.

Firstly, be aware that by default the children will be proxies. They will be loaded one at a time (when accessed). You can change the mapping in various ways to alter this behaviour.

If you want to retrieve the children in batches you can set the batch size. If you want to retrieve them all in one go you can use subselect fetching.

Check the docs for a complete list of fetching strategies: http://docs.jboss.org/hibernate/core/3. ... e-fetching

HTH,
Jordan