May I retrieve partial columns (properties) only?

hsini_huang · **Joined:** Thu May 04, 2006 12:31 am **Posts:** 3

Hi,
I have one mapping file for a large table, which has more than 100 columns. Is there any way to just retrieve several columns and set other properties null? I hope I can get the collection of objects instead of just a resultset.
Thanks!

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

If you use different classes for each "bit" of the table, then yes. You can't partially load objects, but you can break up tables into multiple classes. Hibernate will handle them correctly.

I do this from time to time. My approach is to put the "important" fields into the main class, then use one-to-ones to other classes that are mapped to the same table for the rarely-loaded/saved columns. To get the other columns, I just have to call myMainClass().getIncidentalObject(), or whatever.

hsini_huang · **Joined:** Thu May 04, 2006 12:31 am **Posts:** 3

Thanks! It's very helpful.
But what if the columns are all important and my usage model is that I may pick part of them to show in one page and another ones to show in another page. Does it mean I have to create many mapping files with classes for each page? Is it worthy to do that? I can forsee there might be some (class + mapping files) management issues after production.
BTW, in my usage model, the classes which map to the same table may be used as data fetching only. It's like database view. I may not do any insert/update/delete. Is there any option in mapping file that I can set to prevent users to do that? Thanks!

bkmr_77 · **Joined:** Tue Apr 25, 2006 12:04 pm **Posts:** 260

hsini_huang wrote:

BTW, in my usage model, the classes which map to the same table may be used as data fetching only. It's like database view. I may not do any insert/update/delete. Is there any option in mapping file that I can set to prevent users to do that? Thanks!

This link http://www.hibernate.org/hib_docs/v3/re ... n-property will help you regarding read-only derived properties by specifying insert="false" and update="false". Dont know if you were looking for something like that.

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

Also, <class mutable="false"> essentally puts insert="false" update="false" on every property, and additionally allows for some minor performance updates when creating entity persisters and derived SQL.

You can put multiple mappings in each file. So you can use one file to set up different classes for different parts of the table. If the "important" class includes lazy associations to the other classes, then you don't have to worry about anything after you've written the mapping file.

hsini_huang · **Joined:** Thu May 04, 2006 12:31 am **Posts:** 3

Thanks! Now I know how to design.