Is it possible to dynamically change Fetch types?

fdasprom · **Joined:** Sat Mar 10, 2007 2:43 am **Posts:** 4

Is it possibly to dyamically change Fetch.type? I have an entity that is used in a high transaction application and I want to optionally retrieve associations. ie. Either the associations will be all used or none at all. Lazy loading is not an option because it will result in too many atomic queries being executed.

I guess what I really want is to use is FetchType.EAGER (always creates an efficient single query) with the option to dynamically disable the Fetching of assocations.

batmat · **Posted:** Sat Mar 10, 2007 10:56 am

It is obviously possible. This kind of choices are what is called a "fetch plan". What is in your mappings is only the default behaviour.

Maybe you could show the query you tried. I don't know JPA very well as I'm using Hibernate directly. But with the criteria API, forcing a join is just a matter of calling setFetchMode("theRelation", FetchMode.JOIN);.

With HQL, just add "left join theRelation" to your expression, and you're done.

pledge · **Joined:** Sun Jan 14, 2007 2:52 pm **Posts:** 19

I am trying to use a FetchMode.join in a criteria as you have described. I think I may be misunderstanding what the result should be.

My simple classes are Account and User, where an Account can have many users and and user can have one account.

Account:

Code:

public class Account implements Serializable {
...
@OneToMany(mappedBy="account", cascade = { CascadeType.PERSIST, CascadeType.MERGE })
private Set<User> users = new HashSet<User>();
...
}

User:

Code:

public class User implements Serializable {
...
@ManyToOne (targetEntity=org.martingilday.webapp.domain.Account.class)
@JoinColumn (name="FK_AccountID", nullable=false)
private Account account;
...
}

My query is as so

Code:

return session.createCriteria(getPersistentClass()).setFetchMode("users", FetchMode.JOIN).list();

I am trying to load all accounts and have each of their user collections constructed using just one sql statement. However when I use FetchMode.JOIN I end up with more results than anticipated. If I have two accounts each with three users then the size of my list will be six. It was my understanding that Hibernate would translate the resultset into 2 account objects with the correct users attached. Is this not the case?

pledge · **Joined:** Sun Jan 14, 2007 2:52 pm **Posts:** 19

Answering my question : http://forum.hibernate.org/viewtopic.ph ... 13#2343613

batmat · **Posted:** Sun Mar 11, 2007 5:45 pm

Yes. Indeed.

Try this instead, it should do what you were expecting at first:

Code:

return session.createCriteria(getPersistentClass()).setFetchMode("users", FetchMode.JOIN).setResultTransformer(ICriteria.DISTINCT_ROOT_ENTITY).list();

HTH :-)