1:1 query using an extent

[Andrew Geery <ge...@doc.state.sc.us>]

I am having trouble with the following 1:1 query.

Class AB is a super-class of class A (A is derived from AB). Classes A 
and AB map to the same table.
Class C stores a reference to an object of class A (in an instance 
variable named a).

The problem is that when I attempt to instantiate class C, an object of 
class AB is created, not of type A (from watching the debug output). 
Then I get an exception because an object of class AB is being assigned 
to a variable of class A.

My question is: How do I get an object of class A rather than class AB 
instantiated? I'm confused as to why it is not, given that in the 
reference-descriptor element I am explicitly requesting an object of 
type A. I suspect that I am missing an extent somewhere, but I just 
don't see where it is.

Any help would be greatly appreciated.
Andrew

===================================================

The error looks like this:
[org.apache.ojb.broker.metadata.fieldaccess.PersistentFieldDefaultImpl] 
ERROR: while set field:
object class[ C
target field: a
target field type: A
object value class: AB
object value: AB@...
[org.apache.ojb.broker.accesslayer.RsIterator] ERROR: Error setting 
field:a in object:C

===================================================

In my repository.xml file, I have the following:

<class-descriptor
     class="AB" ...
  >
  <extent-class class-ref="A" />
  <field-descriptor
        name="z"
        column="Z"
        jdbc-type="VARCHAR"
        primarykey="true"
     />...
</class-descriptor>


<class-descriptor
        class="A"...
 >
<field-descriptor
        name="z"
        column="Z"
        jdbc-type="VARCHAR"
        primarykey="true"
     />...
</class-descriptor>


<class-descriptor
        class="C"...
  >
  <field-descriptor
        name="z"
        column="Z"
        jdbc-type="VARCHAR"
        primarykey="true"
     />
     <reference-descriptor
        name="a"
        class-ref="A"
     >
       <foreignkey field-ref="z"/>
     </reference-descriptor>
</class-descriptor>

Re: 1:1 query using an extent

[Thomas Mahler <th...@web.de>]

Hi Andrew,

1.
remove the line
   <extent-class class-ref="A" />

from the AB class-descriptor.

2. If you do not like 1. you have to define the mapping of AB<-A 
hierarchie to one table properly. Follow the steps in tutorial3.html 
(mapping an inheritance hierarchie to one table). You will have to use a 
special attribute ojbConcreteClass to help OJB to instantiate the proper 
class.

cheers,
thomas

Andrew Geery wrote:
> I am having trouble with the following 1:1 query.
> 
> Class AB is a super-class of class A (A is derived from AB). Classes A 
> and AB map to the same table.
> Class C stores a reference to an object of class A (in an instance 
> variable named a).
> 
> The problem is that when I attempt to instantiate class C, an object of 
> class AB is created, not of type A (from watching the debug output). 
> Then I get an exception because an object of class AB is being assigned 
> to a variable of class A.
> 
> My question is: How do I get an object of class A rather than class AB 
> instantiated? I'm confused as to why it is not, given that in the 
> reference-descriptor element I am explicitly requesting an object of 
> type A. I suspect that I am missing an extent somewhere, but I just 
> don't see where it is.
> 
> Any help would be greatly appreciated.
> Andrew
> 
> ===================================================
> 
> The error looks like this:
> [org.apache.ojb.broker.metadata.fieldaccess.PersistentFieldDefaultImpl] 
> ERROR: while set field:
> object class[ C
> target field: a
> target field type: A
> object value class: AB
> object value: AB@...
> [org.apache.ojb.broker.accesslayer.RsIterator] ERROR: Error setting 
> field:a in object:C
> 
> ===================================================
> 
> In my repository.xml file, I have the following:
> 
> <class-descriptor
>     class="AB" ...
>  >
>  <extent-class class-ref="A" />
>  <field-descriptor
>        name="z"
>        column="Z"
>        jdbc-type="VARCHAR"
>        primarykey="true"
>     />...
> </class-descriptor>
> 
> 
> <class-descriptor
>        class="A"...
>  >
> <field-descriptor
>        name="z"
>        column="Z"
>        jdbc-type="VARCHAR"
>        primarykey="true"
>     />...
> </class-descriptor>
> 
> 
> <class-descriptor
>        class="C"...
>  >
>  <field-descriptor
>        name="z"
>        column="Z"
>        jdbc-type="VARCHAR"
>        primarykey="true"
>     />
>     <reference-descriptor
>        name="a"
>        class-ref="A"
>     >
>       <foreignkey field-ref="z"/>
>     </reference-descriptor>
> </class-descriptor>
> 
> 
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