mapping: two object types in one set - to two tables

ffvanderlaan · **Joined:** Wed Sep 07, 2005 6:01 am **Posts:** 4

I have a set with two different kinds of objects (different classes, inherit the same class though).

How do you map this set into two different tables? (each object type has its own table)

Frank

matt_mcgill · **Joined:** Wed Jul 13, 2005 2:18 pm **Posts:** 44

Sounds like you have a 'table-per-concrete class' situation. Refer to sections 10.1.5 and 10.1.6 of the hibernate user manual for more information.

ffvanderlaan · **Joined:** Wed Sep 07, 2005 6:01 am **Posts:** 4

It seems I haven't been very clear. I already store my objects correctly, but need to change something to them when they're in a group. This is my group mapping file, which has to be changed:

Code:

   <hibernate-mapping>
    <class name="project.beer.group.Group" table="groups" lazy="false">
        <id name="id" column="group_id">
          <generator class="increment"/>
       </id>
<set name="grolsches" table="grolsches">
           <key column="gr_group_id"/>
            <one-to-many class="project.beer.grolsch.Grolsch"/>   
       </set>
      <set name="heinekens" table="heinekens">
           <key column="he_group_id"/>
            <one-to-many class="project.beer.heineken.Heineken"/>   
       </set>       </class>

</hibernate-mapping>  

As you can see I have a java class "Group" with a set of Grolsch objects and a set of Heineken objects.

I want them in one set with "Beer" objects (they extend the Beer class), but in that case I will have to seperate them in the mapping file I guess? (because they change something in different tables) How can I do so?

(I do not prefer the workaround : making a "groupId" in the Group.java)

ffvanderlaan · **Joined:** Wed Sep 07, 2005 6:01 am **Posts:** 4

(I do not prefer the workaround : making a "groupId" in the Beer, or Heineken+Grolsch class)

I mistyped.

sdknott · **Joined:** Tue Oct 07, 2003 10:20 am **Posts:** 77

Do the beers have a common super-class? If so, then you can change the mapping to something like the following:

Code:

<hibernate-mapping>
   <class name="project.beer.group.Group" table="groups" lazy="false">
      <id name="id" column="group_id">
         <generator class="increment"/>
      </id>
      <set name="beers">
         <key column="gr_group_id"/>
         <one-to-many class="project.beer.BeerSuperClass"/>
      </set>
   </class>
</hibernate-mapping>

You may find the following section of the documentation useful: http://www.hibernate.org/hib_docs/v3/reference/en/html_single/#inheritance

Looking at your current mapping files, the Table per class hierarchy looks like it will fit well.

Also, you don't need to specify a table in your set mappings if the association is a one-to-many, as it will be placing a foreign-key in the table of the associated class automatically. The table attribute is only necessary with many-to-many mappings.

sdknott · **Joined:** Tue Oct 07, 2003 10:20 am **Posts:** 77

Seems there have been a few replies since I first opened the post, so matt_mcgill is correct in his suggestion.

You just need to map your Beer super-class, along with its sub-classes correctly.

ffvanderlaan · **Joined:** Wed Sep 07, 2005 6:01 am **Posts:** 4

Yes, I changed my "Table per concrete class, using implicit polymorphism" to "Table per class hierarchy" and it works fine. Thanx!