Field from chield table as a key of Map on many-to-many RS.

lamaral · **Posted:** Wed Sep 26, 2007 2:07 pm

Hi,

I have a special requirement for a mapping that I can't found how to do after more than 10 hours of "Googling". I will try to explain here to see if anyone can help.

Quote:

I have these tables:

What I would like to map to the objects as follow:

1- The first level class represents the first table "Equipment" what have one Map attribute that I need to use the OperationName as the key (here is the problem).

2- The second level class in the map, what represents the table "Operations", have a List o commands and command are mapped on another class (third). But here, I need to order the List according the field CommandOrder from the COMMANDS table. (It's ok if I need to move this field to the n:m table, but not the first one.)

Then, the main problem for me is the first item. What I can do to map the field from a chield table to be a key of the Map on a many-to-many relation?

Please, any help is welcome.

Thanks,
Luis Amaral.

Need help with Hibernate? Read this first:
http://www.hibernate.org/ForumMailingli ... AskForHelp

Hibernate version:

Mapping documents:

Code between sessionFactory.openSession() and session.close():

Full stack trace of any exception that occurs:

Name and version of the database you are using:

The generated SQL (show_sql=true):

Debug level Hibernate log excerpt:

Problems with Session and transaction handling?

Read this: http://hibernate.org/42.html

wolle78 · **Joined:** Fri Nov 16, 2007 10:42 am **Posts:** 6

You can use the "formula" tag for selecting a secondary field as the map key from the child table. That is also my current solution.
However, I think this is not very efficient. If anyone has got a better solution I, please share thoughts.

Here's what I'd do (in class Equipment):

Code:

      <map name="operations" table="equipment_operation" cascade="none" lazy="false" fetch="subselect" >
         <key column="equipmentId" not-null="true" />
         <map-key type="string" formula="(select o.operationName from operations o where o.operationId = operationId )" />
         <many-to-many column="operationId" class="Operation" />
      </map>