Hi all,

I have been struggling with lazy loading exceptions.

I am developing desktop application, so open session in view filter is not applicable to me.


I thought that, i can open the session at the start of the program and close when the program ends. Every save/update is flushed-commited. Every query result objects are refreshed by calling refresh() on every individual object.

Transaction is independent of session lifetime.

The program is multi-user application with no app. server. A client-db application.


What problems do you think i can encounter with this design?

Bear in mind that a session, object, for as long as it exists, will hold a database connection.

Moreover, if the application is multiuser, the unflushed sessions of 2 different users will continue to grow, likely holding different data. Even if you flush often, your session will differ, unless you were constantly merging everything all the time.

In my opinion, you should painfully work with events (buttons pushed, windows activated, windows closed, lists clicked) and quickly open/close new, short sessions as needed.

The problems you will get:
- a big memory leak: The session keeps every entity in a big map after it touches it once. So after some time you will have the complete database in memory (assuming you have that much memory)
- stale data problems: By default the session keeps the original state of an entity. If you want to see the current state (changed by a different instance of your app for example) you'll have to refresh manually ... and I personally hate everything with 'manually' in it, because it is error prone
- inconsistent data: Now if you refresh part of your objects, you might work with some objects from the beginning of the day, and other from just now ... not a nice situation

The single session aproach works if your application gets restartet often and doesn't use to much data in a single run.

I'd recommend using one session per Dialog/Frame, except for modal Dialogs which use the session of their parent Dialog/frame. Use a Director pattern to control the Frames and their respective Sessions. I wrote a blog article about Hibernate in 2-tier applications (it's german, but maybe it is of some help anyway)[/url]

thank you very much

I actually just created a english version of that article:

http://blog.schauderhaft.de/2008/09/28/ ... lications/