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List:       ojb-user
Subject:    Re: Problem with Mapping Inheritance Hierarchies
From:       Björn_Voigt <bvoigt () hs-harz ! de>
Date:       2004-03-26 12:43:14
Message-ID: c418b4$q9k$1 () sea ! gmane ! org
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Hello again,

I have still problems with mapping inheritance hierarchies.
I solved my first problem with nonfilled extend fields in the
subclass, but I still recieve two instances of one row.

My tables contains the following rows

select * from a;
  id | some_value_from_a
----+-------------------
   1 |              1000
   2 |              1000

select * from b;
  id | a_id | some_value_from_b
----+------+-------------------
   1 |    2 |              2000


A query has the this result ( there are two instances of B for one Row)

class test.B id:2 a_value:1000 b_value:2000
class test.B id:2 a_value:1000 b_value:2000
class test.A id:2 a_value:1000



Björn Voigt schrieb:
> Hello OJB'lers,
> 
> I have a problem to map Inheritance Hierarchies, I'am the using the third
> proposal of the tutoriala and mapping each class to a distinct table.
> 
> I have the following Classes:
> 
> 1. A and B implements ABInterface
> 2. B extends A
> 
> public class A implements ABInterface{
>   int id;
>   int someValueFromA;
> 
>   public String toString() {
>      return this.getClass() + " id:" +id +" a_value:" + someValueFromA;
>   }
> }
> 
> public class B extends A {
>   int id;
>   int someValueFromB;
> 
>   public String toString() {
>      return super.toString() + " b_value:" + someValueFromB;
>   }
> }
> 
> My Mapping looks so:
> 
> <class-descriptor class="test.ABInterface">
>   <extent-class class-ref="test.A"/>   
>   <extent-class class-ref="test.B"/>   
> </class-descriptor>
> 
> <class-descriptor class="test.A" table="a">
>   <field-descriptor name="id" column="id" jdbc-type="INTEGER" 
> primarykey="true" autoincrement="true" />
>   <field-descriptor name="someValueFromA" column="some_value_from_a" 
> jdbc-type="INTEGER" />
>   <extent-class class-ref="test.B"/>   
> </class-descriptor>
> 
> <class-descriptor class="test.B" table="b">
>   <field-descriptor name="id" column="a_id" jdbc-type="INTEGER" 
> primarykey="true" autoincrement="true" />
>   <field-descriptor name="someValueFromB" column="some_value_from_b" 
> jdbc-type="INTEGER" />
>   <reference-descriptor name="super" class-ref="test.A">
>     <foreignkey field-ref="id" />
>   </reference-descriptor>
> </class-descriptor>
> 
> And the table looks:
> 
> CREATE TABLE A ( ID   INT PRIMARY KEY, SOME_VALUE_FROM_A  INT)
> CREATE TABLE B ( A_ID INT NOT NULL,    SOME_VALUE_FROM_B  INT)
> 
> Table A contains to rows:
> 
>  id | some_value_from_a
> ----+-------------------
>   1 |              1000
>   2 |              1000
> 
> Table B cointains a refenrence to the second row in B
> 
>  a_id | some_value_from_b
> ------+-------------------
>   2   |              2000
> 
> 
> Ok, what I want is to query the ABInterface and get two objects,
> one instance of A and one of B (because id=2 and a_id=2) but what I get 
> is one
> instance of A (OK thats right), but two instaces of B. And the b instances
> cointains no value for the some_value_from_a field. A query have 
> following result:
> 
>     [...]
> 
>     Query q = QueryFactory.newQuery(ABInterface.class, c);
>     Iterator iter = broker.getCollectionByQuery(q).iterator();
>     while (iter.hasNext()) {
>         ABInterface element = (ABInterface) iter.next();
>         System.out.println(element.toString());
>     }
> 
>     [...]
> 
> class test.B id:0 a_value:0 b_value:2000
> class test.A id:1 a_value:1000
> class test.B id:0 a_value:0 b_value:2000
> 
> What I want is:
> class test.A id:1 a_value:1000
> class test.B id:2 a_value:1000 b_value:2000
> 
> Could anyone tell what I do wrong or is it possible what want to do? ;-)
> 
> Thank you for help
> 
> Björn Voigt



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