Re: Inheritance: One Table

[Tino Sch�llhorn]

Hi,
unfortunately I still have one problem:
I use a xml-parser to pre-validate the repository.xml-file. This Parser 
now complains that field-descriptors cannot be used when using extent. I 
checked that with the DTD and I think it is correct:

<!ELEMENT class-descriptor
        ((documentation?, extent-class+, attribute*) |
        (documentation?, object-cache?, extent-class*, field-descriptor+,
         reference-descriptor*, collection-descriptor*,
     index-descriptor*, attribute*,
     insert-procedure?, update-procedure?, delete-procedure?))>
But the thing is: OJB works correctly. So what do I do now? Should I 
ignore this warning? Or do I have to create a not-persistent abstract
superclass?

Tino

Thomas Dudziak wrote:
Tino Sch�llhorn wrote:
Hi,
I have I inheritance-problem. I want to map two classes to one table. 
They are defined as followed:

class A {
    int id;
    protected String ojbConcreteClass;
    // some attributes   }
class B extends A {
    // some additional attributes
}
I created class-descriptors for each of the table:
<class-descriptor class="A" table="table">
    // field-descriptors for A inluding ojbConcreteClass
</class>
and
<class-descriptor class="B" table="table" extends="A">
    // additional field-descriptors for B
</class>
So: When I try to store an instance of Type A everything is fine. But 
when I try to store an instance of Type B OJB complains:

Caused by: 
org.apache.ojb.broker.metadata.ClassNotPersistenceCapableException: 
OJB needs at least one primary key attribute for class 
objectsRealClass=class kos.wnetz.om.RelationHistoryEvent, 
objectTopLevelClass=class kos.wnetz.om.RelationHistoryEvent
    at 
org.apache.ojb.broker.Identity.checkForPrimaryKeys(Identity.java:245)
    at org.apache.ojb.broker.Identity.init(Identity.java:121)

So I also tried to include the field-descriptors of the superclass in 
the class-descriptor for class B. But then I get an even worse error:

Caused by: java.sql.SQLException: Parameter index out of range (8 > 7).

I don't know where this exception comes from, but in order to describe a 
super-subtype relationship you should use something like:

<class-descriptor class="A" table="table">
    <extent-class class-ref="B"/>
    // field-descriptors for A inluding ojbConcreteClass
</class>
and
<class-descriptor class="B" table="table">
    // field-descriptors for B including ojbConcreteClass
</class>
The extent-class is inverse to the extends/implements in Java (i.e. 
specified at the supertype), and also note that the class-descriptor for 
B contains all attributes of A (there is no automatic 'inheritance' of 
the descriptors in the repository.xml file) including the 
ojbConcreteClass attribute.

Tom

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