Re: Difficultity with abstract mapping

[Armin Waibel]

[EMAIL PROTECTED] wrote:
Hi Armin,
yes - I tried defining an extent and the appropriate 
class-descriptor's - I also experimented with 
"super".  I assume that I am correct in assuming 
that it "is" possible to build such a structure with 
an abstract class?

yep, I wrote a test case (using "extent" and different tables, as 
described on my last post) on my local machine and it work without 
problems (store/delete graph of objects).
Pay attention not to mix different mapping strategy, e.g. use "extent" 
and "super" for the same classes, this could cause side-effects.

It should also be possible store the whole graph in one table using 
"ojbConcreteClass" feature.

regards,
Armin
regards,
Marcus


Hi Marcus,
did you try to declare class-descriptor's for B and C (including all 
fields and references) and define an extent for class A:

<class-descriptor class="A">
  <extent-class class-ref="B" />
  <extent-class class-ref="C" />
</class-descriptor>
regards,
Armin
Marcus Young wrote:

Hi,
I have just been working an issue related to mapping abstract classes.  
I've read quite a lot about it but I'm still unclear.  The structure I 
have is as follows:

Abstract Class A which can hold a collection of  'A' objects.
Classes B and C which extend A
Each class is mapped to a separate table.
I am  hoping to be able to retreive records in such a way as to 'build' 
an 'A' class object including the objects collection which may include 
objects of class B and C.   So far I have been working with 'super' and 
'extents' - but to be honest I'm not really sure how to get it working.  
Most commonly I'm getting exceptions of "InstantiationException". -  
this appears to be related to the abstract 'A' class?  I can resolve 
this particular exception by using a concrete class, however I 
particularly wanted to use an abstract class.  Any assistance would be 
greatly appreciated.

I end up with something like this:
public abstract class A extends TransferObject
{     protected Long _id;
}
public class B extends A
{
  private String _name;
  private String _description;
*}
*public class C extends A
{
  private String _name;
  private String _description;
*}
*   <class-descriptor
    class="com.eclipsej.permission.A" table="A">
       <field-descriptor
          name="_id"
          column="ID"
          jdbc-type="BIGINT"
          primarykey="true"
          autoincrement="true"
       />
       <!-- extent-class class-ref="com.eclipsej.user.B" / -->
  </class-descriptor>  
<!-- Defnitions for com.eclipsej.user.B -->
 <class-descriptor class="com.eclipsej.user.B" table="roles">
    <field-descriptor name="_id" column="ID" jdbc-type="BIGINT" 
primarykey="true" autoincrement="true"/>
    <field-descriptor name="_name" column="NAME" jdbc-type="VARCHAR"/>
    <field-descriptor name="_description" column="DESCRIPTION" 
jdbc-type="VARCHAR"/>         <reference-descriptor name="super" 
class-ref="com.eclipsej.permission.A"
       auto-retreive="true" auto-update="true" auto-delete="true">
       <foreignkey field-ref="_id"/>
    </reference-descriptor>    </class-descriptor>*
*

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