aspose file tools*
The moose likes Object Relational Mapping and the fly likes How to lazily load references when the object is detached from session ? Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login
JavaRanch » Java Forums » Databases » Object Relational Mapping
Bookmark "How to lazily load references when the object is detached from session ?" Watch "How to lazily load references when the object is detached from session ?" New topic
Author

How to lazily load references when the object is detached from session ?

Kumar Raja
Ranch Hand

Joined: Mar 18, 2010
Posts: 518
    
    2

Hi All,

I have read that in order to lazily load objects and its references, the object and its references should always be attached to a session. This makes sense as, the proxies are associated with the session and out of session proxies does not have any value and can not be used. However, in most of the cases, especially in a multitier environment, a client's request may pass through many layers and at some where below the stack, the objects are retrieved under a session and returned back to calling object. In the calling object, there may/may not be having any references to session (may be that is completely unaware of a thing called Hibernate). In such cases, how can the objects and its references be still loaded lazily. I may better explain my question using an example.

Assume, I have two entities Person and Event.
Every Person can attain one or more events and I'm having a one-many unidirectional association between Person and Event.

Person.java


Person.hbm.xml


Event.java


Event.hbm.xml


After defining these files, I'm using a client application to persist Events and Persons and establishing associations between these two. I'm successful till here.

Now, I'm attempting to retrieve objects and my method is as follows


As you can see from this method this is returning only the proxies as I'm using load method instead of get. But when I try to invoke the method


on the reference I get for these objects, I get exception [b]1203 [main] ERROR org.hibernate.LazyInitializationException - could not initialize proxy - no Session. [b]. I can understand the reason for this exception, as at this point, object being referred by "e" is not associated with any session.

I can quickly overcome this issue, if I use "get" instead of "load", though I'm more interested in using load.

But what if, Event has references to some other entities, say "Address". How can I call
e.getAddress() like method, when I'm completely out of session control, except that I mention the reference retrieval as eager loading.

Is there any work around, where I can access objects and their references lazily, but yet outside a hibernate session.

Thanks

Regards
KumarRaja

David Newton
Author
Rancher

Joined: Sep 29, 2008
Posts: 12617

No, you need to be attached to a Hibernate session--this seems self-evident to me.

Options include using an OSiV-style filter or loading more data earlier in the process.
 
jQuery in Action, 2nd edition
 
subject: How to lazily load references when the object is detached from session ?