Thanks a lot (Samuel too).
> On 22. 8. 2016, at 8:29 PM, Chuck Hill <[email protected]> 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: <[email protected]> on behalf
> of OC <[email protected]>
> Date: Monday, August 22, 2016 at 6:36 AM
> To: WebObjects-Dev Mailing List <[email protected]>
> 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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