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From Craig Russell <Craig.Russ...@Sun.COM>
Subject Re: Question on TCK11
Date Sat, 21 May 2005 21:57:21 GMT
Hi Geoff,

On May 21, 2005, at 12:53 PM, Geoff hendrey wrote:

> Department.hashCode method is using a persistent field
> to compute the value of the hashcode, in TCK11. Note
> that in the Sun version of the TCK, which JDOMax
> passes, hashCode is NOT overidden for Department.
> I think it is wrong to override hashCode and equals
> for any class using datastore identity.

The decision to override hashCode and equals belongs to the 
application, not to the JDO implementation. These methods implement the 
application's notion of equality, which as is well-described in the JDO 
specification, is different from both identity (the JVM's way of 
distinguishing whether two instances are the same) and JDO identity. 
That's why we have JDO identity.

> This was the
> subject of 35 or so emails on the experts group, and
> this was the position espoused by Craig.
> Craig laid down the law:
> "If you don't have a set of fields that uniquely form
> an application identity, then you should not implement
> equals. You *should* delegate to Object.equals"

The classes in question have a set of fields that uniquely form an 
application identity, and hashCode and equals use these fields. I don't 
see the issue.
> Please let me know if an implementation is expected to
> handle cases when the user overides equals and
> hashCode for datastore identity?

Yes. The three forms identity, equality, and JDO identity are given 
equal weight in the Java specification, the java.util classes, and the 
JDO specification. Identity belongs to the VM; equality belongs to the 
application; JDO identity belongs to the implementation.


> Certainly, JDOMax
> does NOT, and is failing a good bit of the Apache
> TCK11 because of it!
> -geoff
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Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:Craig.Russell@sun.com
P.S. A good JDO? O, Gasp!

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