nested list mapping

RedSnapper · **Joined:** Tue Sep 01, 2009 3:22 am **Posts:** 5

Hi,

i have the following classes: MyClass, YourClass and HisClass

MyClass contains a List of YourClass
and
YourClass contains a List of HisClass

so I have a class (MyClass) that contains a List of Objects (YourClass), each of which contains a List of more Objects (HisClass)...

so I map:

Code:

<hibernate-mapping>
   <class name="MyClass" table="myclass">
      ...
      <property name="someproperty" />
      ...
      <list name="yourclass" table="myclass_yourclasses">
         <key column="myclass_id" />
         <list-index column="position" />
         <composite-element class="YourClass">
            ...
            <property name="someproperty" />
            ...
            <list name="hisclass" table="myclass_yourclasses_hisclasses">
               <key column="yourclass_id" />
               <list-index column="position" />
               <composite-element class="HisClass">
                  ...
               </composite-element>
            </list>
         </composite-element>
      </list>
   </class>
</hibernate-mapping>

but Hibernate would NOT let me use this mapping.
How would I do that?

Thanx for some hints.
Cheers
Björn

Cameron McKenzie · **Posted:** Tue Sep 08, 2009 10:48 am

Don't nest the List mappings, but instead, map the objects separately, each with its own contained list.

Masterplan79th · **Joined:** Fri Jun 26, 2009 6:59 am **Posts:** 23

From my own documentation, a piece of note.

The first issue to note when using One-to-Many is that Hibernate cannot fetch multiple ordered collections together, you’ll see the exception:
org.hibernate.HibernateException: cannot simultaneously fetch multiple bags
In order to get around this, you need to define your Collection specifically as a Set, since Set is explicitly unordered, Hibernate can deal with as many multiple sets as you wish to use.

Cameron McKenzie · **Posted:** Tue Sep 08, 2009 5:09 pm

Quote:

cannot simultaneously fetch multiple bags

I believe that if only one of the associated lists is eager, you can get around this. It's largely when there are multiple bags being eagerly loaded that you hit problems.