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With JPA how can I force loading of nested lazy collections?

Brick Riccardi
Greenhorn

Joined: Jun 01, 2008
Posts: 22
(I also posted this on a jboss jpa forum and haven't received a response yet, so trying here as well...)

I'm new to JPA (and Hibernate for that matter. Come from iBATIS background.)

Take a case where you have a Company object which contains a List of Employees, and each Employee object has List of Address objects and List of Preferences (Address and Preference would be another domain models.)

I obviously don't want to to return some of the nested items all of the time, so lazy seems to be fine for the nested collections, and typically I suppose I should use 'join fetch' to pull back some of the nested items. However, in the Employee object there are two Collections and I've read it's not a good idea (if even possible?) to join fetch two different collections within the same object.

My question is how can I force the lazy loading of some objects so that they are all populated without traversing the entire nested structure and having to call the getter on the lazy fields just to get them populated?

It looks like in Hibernate you can call Hibernate.initialize(yourObject.getYourCollection) and it will initialize the lazy load of the objects, which is bit cleaner than yourObject.getYourCollection.size(). But not sure how to accomplish the same thing with just standard JPA syntax?

Also how does this work if you are nested more than one level and I need my nested lazy collections also populated? (For example maybe I need the whole object tree populated before sending it to the web tier or off to some other business process outside of the scope of my EntityManager.)

Maybe I can manually set the fetch type to Eager for those domain models before performing my specific query? I haven't seen an example of that done though.

Thanks for any help.
Daniel Melo
Greenhorn

Joined: Oct 19, 2006
Posts: 3
UP,

Experiencing the very same problem
Kadle Rajesh
Greenhorn

Joined: Jan 16, 2007
Posts: 11
In your case, you need to declare "outer-join=true" on the collections and also set "hibernate.max_fetch_depth" to retrieve the collections.

If collections are declared lazy, we can use the below command to initialize the collections before closing session:



Jigar Naik
Ranch Hand

Joined: Dec 12, 2006
Posts: 751
Upto what extent does this initialize collection ?
What if the object in the collection contains another collection... ?


Jigar Naik


Daniel Melo
Greenhorn

Joined: Oct 19, 2006
Posts: 3
Remember we're using JPA, so there is no Hibernate.initialize.

Let's say, I've the following class design:

Every collection is lazy loaded by default.

I'd like to get all Roles of a particular User. The point is, each single Role returned must have it's Permissions eagerly loaded as well. The JPQL query:
must be changed to accomplish this.
I've tried different combinations with join fetch, with no success.

Any help?

thanks!
samy omar
Greenhorn

Joined: Jul 21, 2007
Posts: 3
I found a solution for what you asked, I know that it will not help you to get answer after around 3 years
But i liked to reply to help other poeple searching for the same solution

You can join fetch option like this example.
createQuery("select c from Category as c" + " left join fetch c.categorizedItems as ci" + " join fetch ci.item as i");


 
I agree. Here's the link: http://aspose.com/file-tools
 
subject: With JPA how can I force loading of nested lazy collections?
 
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