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From Craig Russell <Craig.Russ...@Sun.COM>
Subject Re: JDO TCK Conference Call Friday, Aug 12, 9 am PST
Date Sat, 13 Aug 2005 00:14:47 GMT
Hi Andy,

On Aug 12, 2005, at 12:16 PM, Andy Jefferson wrote:

>> Issue 106 is the biggest single problem. It is about mapping Object
>> fields, which are covered in the specification. Section 6.4.3 says
>> the implementation must support Object fields as First Class Objects.
> OK, but the wording of that part of the spec was discussed in the  
> EG back on
> 02 April 2005 (thread titled "updates to tck11 project", for those  
> with EG
> access) and the general conclusion was that it was totally vague,  
> and maybe a
> JDO implementation should be able to map "some PC type" to that  
> Object field
> but how it can be testable by the TCK is open to debate. How does  
> the JDO
> impl know that this Object field can only be a "SimpleClass" PC object
> maybe ? There's no info that I can see in the metadata to define this.

Good point. I was thinking perhaps we should use the same technique  
that we have already used to good effect with collections and maps.

What if we define a new attribute on field called field-type, and for  
the TCK we put in "...SimpleClass"? Would that allow you to map it?

The issue is that Object types need to be supported, but as you point  
out, there's not enough metadata to give an implementation a clue how  
to do it.

What do you think? If it's doable, I can raise it to the jdo-experts.

Thanks for your quick feedback!


> It's the same problem space as interfaces. With those we have the  
> "implements"
> attribute which tells us which actual types we can store there.  
> Consequently
> JPOX models an interface field as being one FK for each  
> implementation type
> (so if there are 3 possible implementations, then the schema has 3  
> FKs). With
> "Object" we have nothing to go on, so at the time of mapping the  
> schema we
> know that we may have to map something. Clearly the JDO  
> implementation could
> define an extension tag (akin to the JPOX "implementation-classes"  
> that we
> had for interfaces) that defines that this Object field can be  
> represented by
> these 2 PC types, but that becomes not testable by the TCK at that  
> point.
> If there's some action on JPOX from this, just let us know so we  
> can work out
> what is needed.
> -- 
> Andy

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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