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From Craig L Russell <Craig.Russ...@Sun.COM>
Subject Re: Subquery specification update
Date Thu, 25 Oct 2007 16:03:43 GMT
Currently, parameters are only specified to work in the result,  
filter, ordering, grouping, or range parts of a query, not in the  
FROM part.  This is in both the single string version (from  
CandidateClassName ExcludeClause opt) and API version where the  
setCandidates takes either Extent or Collection, not parameter name.

I'm not necessarily opposed to adding the ability to use parameters  
as the candidate collection, but I'd like to hear more details as to  
how a parameter can be used as a candidate collection, and from the  
implementation engineers to see if this change could be done.

The only problem I have with including single string JDOQL to the  
examples is that it would be before the single string JDOQL topic was  
introduced. Would it be better to move all the subquery examples down  
to the examples section?

Craig

On Oct 25, 2007, at 8:37 AM, Michael Bouschen wrote:

> Hi Matthew, hi Christiaan,
>> I agree that the candidateCollectionExpression description is a  
>> bit cryptic.
> Do you have an idea for a better description? The reason to include  
> something like "tokens from this query" is that we have to define  
> the scope for identifiers used in the  
> candidateCollectionExpression. So in "this.department.employees"  
> this denotes the candidate instance of the outer query and NOT of  
> the subquery.
>>
>> Boy, it's been a long time since I thought about subqueries.  Can  
>> we also provide single-string versions of the examples?  That  
>> would be helpful.
> Do you mean add single string JDOQL of the examples to the spec or  
> provide them for this email discussion? I agree it would be useful  
> to add them to the spec. If you are just interested for right now:
> - employees who work more than the average of all employees
> SELECT FROM Employee WHERE this.weeklyhours > (SELECT AVG 
> (e.weeklyhours) FROM Employee e)
> - employees who work more than the average of their department  
> employees
> SELECT FROM Employee WHERE this.weeklyhours > (SELECT AVG 
> (e.weeklyhours) FROM this.department.employees e)
> - employees who work more than the average of the employees in  
> their department having the same manager:
> SELECT FROM Employee WHERE this.weeklyhours >
>   (SELECT AVG(e.weeklyhours) FROM Employee e WHERE e.manager ==  
> this.manager)
>
> Christiaan,
> yes, I think the query code you added to your email returns the  
> same result.
>
> Regards Michael
>
>> -matthew
>>
>> On Oct 25, 2007, at 5:07 AM, Christiaan wrote:
>>
>>>
>>> Hi Craig,
>>> the examples are very informative. I must say that I find the  
>>> description
>>> for candidateCollectionExpression
>>> "The candidateCollectionExpression is the expression using tokens  
>>> from
>>> this query that represent the candidates over which the subquery is
>>> evaluated. "
>>> a little bit cryptic (I actually find the paramater name more  
>>> descriptive
>>> than the description). Especially "tokens from this query" (is  
>>> tokens a
>>> common word for this and may be it should be stressed that this  
>>> query is the
>>> outer query?) and "over which the subquery is evaluated", but may  
>>> be this is
>>> needed for the spec.
>>>
>>> Anyway, do I understand it correctly that it is the same as:
>>> ....
>>> sub.setFilter(":departmentEmployees.contains(this)");
>>> Query q = pm.newQuery(Employee.class);
>>> q.setFilter("this.weeklyHours > averageWeeklyhours");
>>> q.addSubquery(sub, "double averageWeeklyhours",  null,
>>> "this.department.employees");
>>>
>>> kind regards,
>>> Christiaan
>>> -- 
>>> View this message in context: http://www.nabble.com/Subquery- 
>>> specification-update-tf4686785.html#a13405438
>>> Sent from the JDO - Development mailing list archive at Nabble.com.
>>>
>
>
> -- 
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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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