Re: Subquery specification update

[Craig L Russell]

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.

Craig

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

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?

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 >


Christiaan,


Regards Michael

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 AVG(e.weeklyhours) FROM Employee e WHERE e.manager == this.manager) yes, I think the query code you added to your email returns the same result.

-matthew

On Oct 25, 2007, at 5:07 AM, Christiaan wrote:

Hi Craig,

for candidateCollectionExpression

this query that represent the candidates over which the subquery is
evaluated. "

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
--

the examples are very informative. I must say that I find the description "The candidateCollectionExpression is the expression using tokens from 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 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
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P.S. A good JDO? O, Gasp!

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