Re: derived attribute to sum a relationship?
Re: derived attribute to sum a relationship?
- Subject: Re: derived attribute to sum a relationship?
- From: Hugi Thordarson <email@hidden>
- Date: Tue, 23 Aug 2016 14:50:02 +0000
Have you checked out ERXEOControlUtilities.aggregateFunctionWithQualifier? Sounds like it might suit your needs.
- hugi
> On 23. ágú. 2016, at 14:34, email@hidden wrote:
>
> Thanks a lot (Samuel too).
>
>> On 22. 8. 2016, at 8:29 PM, Chuck Hill <email@hidden> wrote:
> ...
>> I can’t think of a way to do that that isn’t a lot of code and prone to inconsistencies with the relationship data.
>
> Hmmm... is there at least some WO or WOnder trick, which would fetch at SQL-level a sum for relationship on-demand, i.e., something like this fetchSumForAttributeInRelationsip hypothetical method:
>
> ClassA eo=...; // an enterprise object of entity A
> Number sum=eo.fetchSumForAttributeInRelationsip("x","ab")
>
> which would _not_ fire the "ab" relationship fault; instead, it would generate and perform an SQL similar to "SELECT SUM(C_X) FROM B_TABLE WHERE ..." (with appropriate WHERE to get those rows of B which are in the 1:N relationship "ab" from "eo")?
>
> Or do I have do go explicitly create and run the SQL expression programmatically?
>
> Thanks,
> OC
>
>> From: <webobjects-dev-bounces+chill=email@hidden> on behalf of OC <email@hidden>
>> Date: Monday, August 22, 2016 at 6:36 AM
>> To: WebObjects-Dev Mailing List <email@hidden>
>> Subject: derived attribute to sum a relationship?
>>
>> Hello there,
>>
>> is there a way to define a derived attribute to sum a relationship's attribute?
>>
>> Presumed I have
>>
>> - entity A with PK column C_ID, relationship:N "ab" leading to entity B
>> - entity B with FK column C_A_ID (which forms the relationship) and integer column C_X representing attribute "x"
>>
>> is it possible to define a derived attribute "abSum" of A, which would sum all "x"'s of those B rows, which are -- through their C_A_ID foreign key -- related to a row in A?
>>
>> Normally, of course, I would implement it Java-side, like this
>>
>> ===
>> class AEntityClass ... {
>> int abSum() {
>> int s=0; for (b in ab()) s+=b.x; return s
>> }
>> }
>> ===
>>
>> but this time, I would need to do that SQL-side, for (a) speed, (b) memory (so that all B rows do not need to be fetched), (c) so that the attribute can be used in qualifiers when fetching, e.g.,
>>
>> ===
>> NSArray objs=ec.objectsWithFetchSpecification(new EOFetchSpecification("A",EOQualifier.qualifierWithQualifierFormat("abSum > 100",null),null))
>> ===
>>
>> I have tried to define it as the most obvious "select sum(bt.C_X) from B_TABLE bt where bt.C_A_ID = C_ID", but I bumped into numerous problems, from ambiguity of C_ID up to the fact that EOF caches the fetched value and does not recache when the relationship objects change, and thus I am getting obsolete values.
>>
>> Is there a way to do that properly?
>>
>> Thanks,
>> OC
>>
>>
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