Re: Mapping fields to subclasses in XML schema

[Gabriel Bauman <ga...@bravenet.com>]

I don't suppose anyone can enlighten me on the below message? I didn't 
hear from anyone. Sorry for the spam, I won't ask again. ;)

Gabe

Gabriel Bauman wrote:
> Hi there. I understand that classes and their subclasses are mapped onto 
> a single table under Torque. What I don't understand is how to specify 
> that a field should only be retrieved in a subclass.
> 
> =====
> public class SuperClass
> {
>    public int FOO;
> }
> 
> public class SubClass extends SuperClass
> {
>    public int BAR;
> }
> =====
> 
> <table name="superclass" javaName="SuperClass">
>   <column name="FOO" type="int" />
>   <column name="BAR" type="int" />
>   <column name="inheritance" inheritance="single" type="CHAR">
>     <inheritance
>        class="SubClass"
>        extends="SuperClass"
>        key="A"
>        />
>   </column>
> </table>
> 
> =====
> I want to be sure that field BAR does not exist in instances of 
> SuperClass, given the fact that they're both mapped on the same table. 
> How should my XML schema look in this situation? I must be missing 
> something simple here.
> 
> Thanks in advance...
> 
> Gabe
> 
> 
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Re: Mapping fields to subclasses in XML schema

[Gabriel Bauman <ga...@bravenet.com>]

Hmm...

> Since you want BAR in SubClass but not in SuperClass, define your schema 
> as below.
> 
> <table name="superclass" javaName="SuperClass">
>   <column name="FOO" type="INTEGER" inheritance="single">
>     <inheritance key="SubClass" class="SubClass" extends="SuperClass" />
>   </column>
> </table>
> 
> <table name="subclass" javaName="SubClass">
>   <column name="BAR" type="INTEGER" />
> </table>

See, this was what I would have thought, but since Torque's 
documentation says it stores superclasses and subclasses in the same 
table, I don't think what you're saying will actually work. The Torque 
Inheritance Guide (http://db.apache.org/torque/inheritance-guide.html) 
does not mention 'subclass' tables.

Can anyone else who uses inheritance in Torque please settle this? Is 
the above mthod actually correct?

Gabe

Re: Mapping fields to subclasses in XML schema

[Eric Emminger <er...@ericemminger.com>]

I'll take a stab at this! :)

 >>> I want to be sure that field BAR does not exist in instances of
 >>> SuperClass, given the fact that they're both mapped on the same
 >>> table. How should my XML schema look in this situation? I must be
 >>> missing something simple here.

Since you want BAR in SubClass but not in SuperClass, define your schema 
as below.

<table name="superclass" javaName="SuperClass">
   <column name="FOO" type="INTEGER" inheritance="single">
     <inheritance key="SubClass" class="SubClass" extends="SuperClass" />
   </column>
</table>

<table name="subclass" javaName="SubClass">
   <column name="BAR" type="INTEGER" />
</table>

So you know, all I did was generate the OM and look at the Java files. 
Everything looks correct, but that's all I did, so I may have missed 
something.

Please, let me know whether or not this works for you.

Eric

Re: Mapping fields to subclasses in XML schema

[Travis McCauley <tw...@virginia.edu>]

I asked a similar question last Wednesday and also got no replies. 
I've also seen similar questions unanswered in the archives. I don't 
think it's possible to map this in the schema. If it was, either 
someone would say or it would be in the tutorial.

I set up a simple interface to maintain the subclass-to-column 
relationships. If a subclass tries to access an inappropriate field I 
just throw an exception. I also had to override the copy() method to 
allow casting back to the subclass.

Please someone let us know if there is an easier way.

Sincerely,
Travis McCauley
Snowy Virginia




>I don't suppose anyone can enlighten me on the below message? I 
>didn't hear from anyone. Sorry for the spam, I won't ask again. ;)
>
>Gabe
>
>Gabriel Bauman wrote:
>>Hi there. I understand that classes and their subclasses are mapped 
>>onto a single table under Torque. What I don't understand is how to 
>>specify that a field should only be retrieved in a subclass.
>>
>>=====
>>public class SuperClass
>>{
>>    public int FOO;
>>}
>>
>>public class SubClass extends SuperClass
>>{
>>    public int BAR;
>>}
>>=====
>>
>><table name="superclass" javaName="SuperClass">
>>   <column name="FOO" type="int" />
>>   <column name="BAR" type="int" />
>>   <column name="inheritance" inheritance="single" type="CHAR">
>>     <inheritance
>>        class="SubClass"
>>        extends="SuperClass"
>>        key="A"
>>        />
>>   </column>
>></table>
>>
>>=====
>>I want to be sure that field BAR does not exist in instances of 
>>SuperClass, given the fact that they're both mapped on the same 
>>table. How should my XML schema look in this situation? I must be 
>>missing something simple here.
>>
>>Thanks in advance...
>>
>>Gabe
>>
>>
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>>
>
>
>
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