Problems with PersistentSet

anderson.araujo · **Joined:** Thu Apr 06, 2006 4:01 pm **Posts:** 7

Hi all,

Is there any way to not use PersistentSet in set mappings ?

My setter method has to iterate over the set, so when Hibernate call the method, an LazyInitializationException is thrown.

The Exception:
12:59:25,832 ERROR [LazyInitializationException] illegal access to loading collection
org.hibernate.LazyInitializationException: illegal access to loading collection
at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:341)
at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:86)
at org.hibernate.collection.PersistentSet.iterator(PersistentSet.java:138)
at java.util.AbstractCollection.addAll(AbstractCollection.java:316)

The method:

Code:

   @SuppressWarnings("unused") private void setInterfaceAttributeList(Set<InterfaceAttribute> interfaceAttributeList) {
      this.interfaceAttributeList = new LinkedHashSet<InterfaceAttribute>();
      if (interfaceAttributeList != null)
         this.interfaceAttributeList.addAll(interfaceAttributeList);
   }

tks

hlfsousa · **Posted:** Wed Jun 28, 2006 2:20 pm

I believe PersistentSet maintains iteration order constant -- it behaves just like a LinkedHashSet, so I suggest you declare the property as a java.util.Set and just assume iteration order is constant.
If you are going to close the session before iterating over this lazy collection just call size() on the collection before closing the session.

batmat · **Posted:** Wed Jun 28, 2006 5:27 pm

Well, in fact there's no point doing it...

Where are you receiving the LazyInitializationException ? Did you close the Hibernate Session before trying to access the collection ?

You should read about the N+1 syndrom with mapping O/R. Typically, here you say that you want to access the collection. You have to understand the principles behind lazy loading.

In fact, lazy loading is quite simple. It's using kind of a java proxy : instead of doing things directly, something is put between. Concerning persisitent collections, even if you weren't using PersistentSet, you'd meet the problem : you get the exception because you're trying to access data which hasn't been loaded yet, while the Hibernate Session is closed. You should iterate once on the collection before this session is closed not to get the exception anymore (that's why hlfsousa tells you to call size() : same result => to know the set size, the set has to be completely iterated over, so it's also wholy loaded).

To illustrate this, and THIS IS Very important when you develop with Hibernate : activate the display of the SQL queries sent to the db (show_sql => true). If you do this, you'll see that iterating on your collection (before session is closed, obviously) triggers a select for each element of the collection.

Is it a bit clearer with this explanation ? Do you have other questions about this ?