Mapping associations

mangrar · **Joined:** Fri Mar 02, 2007 5:01 am **Posts:** 6

Hello. I'm newbie with hibernate. I'm trying to map an association but I'm not sure how to do. I have 3 tables:

USERS( id_usr, name, email....): P.K.: id_usr
USERS_ITEMS( id_usr, id_item, amount): P.K.: (id_usr, id_item)
ITEMS( id_item, name ): P.K.: id_item

As you can see an user can be related with many ITEMS (relation USERS_ITEMS) and an item can be related with many USERS. What I need to do is from Users java class obtain its related ITEMS adding the amount column. I don't know how to perform this relation in the mapping files.

Thanks.

batmat · **Posted:** Wed Apr 25, 2007 1:31 pm

This a special many-to-many case, 'cause there's an additional column. So just create an additional central entity class (or component, that's your prerogative), then map a one-to-many from both sides to this central class.

See reference documentation for this: http://www.hibernate.org/hib_docs/v3/re ... -onetomany or the Java Persistence with Hibernate book.

mangrar · **Joined:** Fri Mar 02, 2007 5:01 am **Posts:** 6

Hi. Thanks for your answer. I can't do that, because there isn't any foreign key from USERS to USERS_ITEMS. USERS_ITEMS have a foreign key to USERS and another one to ITEMS. These foreign keys compose the primary key of USERS_ITEMS. What I want, is from USERS obtaining the ITEMS asociated an adding the amount column in USERS_ITEMS. Let's look an example:

USERS
---------
id_usr | name.....
----------------
00001 | XXXX

ITEMS
-------
id_item | name.......
-----------------
item001| aaaa
item002| bbbb

USER_ITEMS
------------------------------
is_usr | id_item | amount
-----------------------------
00001 | item001| 10
00001 | item002| 25

From an user I'd like to get this:

item001 | aaaa | 10
item002 | bbbb | 25

Do you understand?? At the moment, I've mapped this in USERS.hbm.xml:

<set name="items" table="USER_ITEMS">
<key column="id_usr"/>
<many-to-many column="id_item" class="Item" />
</set>

This association returns the items related to an user, but I need the amount property/column too. The relationship between Users and User_items is 0..n. So, I've thought obtaining a collection of user_items, and then, with each user_items instance, obtain the item. How can I do than?