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Re: Subquery specification update
by Michael Bouschen-2
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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.
>>
--
Tech@Spree Engineering GmbH Tel.: +49/(0)30/235 520-33
Buelowstr. 66 Fax.: +49/(0)30/217 520-12
10783 Berlin mailto:mbo.tech@...
Geschaeftsfuehrung: Anna-Kristin Proefrock
Sitz Berlin, Amtsgericht Charlottenburg, HRB 564 52
> 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.
>>
--
Tech@Spree Engineering GmbH Tel.: +49/(0)30/235 520-33
Buelowstr. 66 Fax.: +49/(0)30/217 520-12
10783 Berlin mailto:mbo.tech@...
Geschaeftsfuehrung: Anna-Kristin Proefrock
Sitz Berlin, Amtsgericht Charlottenburg, HRB 564 52
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