On 12/4/06 3:30 PM, DavidA wrote:
> I think it quickly gets more complicated than that syntax would
> support.
Oh, of *course* it does -- that's why I want to discuss it more!
I think, though, that we should be able to find a 80/20 point for aggregates
and support most of the common use cases. That's pretty consistent with the
rest of Django's ORM: we don't try to model *everything* you can do with SQL,
just most of the common stuff.
I'm totally OK with making complex queries be written in SQL; it actually
turns out that SQL's a really good language for handing lots of data :)
As long as the syntax is nice, it seems that any aggregate support would be
better than none.
> For example, how would you ask for more than one aggregate
> value in that syntax? My common use case is grouping a bunch of
> financial positions, where the SQL would look something like:
>
> select account, count(*), sum(quantity), sum(total_pnl) from
> position
> group by account
>
> Would I have to call queryset.groupby(account) three times: once for
> count(), once for sum(quantity) and once for sum(total_pnl)?
My gut would be that that particular case wouldn't be supported, but::
quantity, total_pnl =
Position.objects.groupby("account").sum("quantity",
"total_pnl")
would work. So maybe you can only do one aggregate operation at once? That
seems to mesh OK with the majority of aggregate usage *I* do...
> And what exactly does queryset.groupby() return?
I was thinking it would return some proxy object that supports .sum(), .avg(),
etc. methods. By itself I don't think it would be very useful.
> My idea was a queryset.groupby() could return some sort of dynamic
> Django model class where the attributes where the aggregated fields
> plus the fields you were grouping by and if you were grouping by a
> relation field, it would magically work like any other model relation.
I don't think I follow here - can you give me an idea of what you're talking
about?
> But I don't know how complicated that would be and I haven't thought of
> a syntax that works nicely for the more complex cases.
Again, I'm OK with just supporting the simple-ish cases if that's all we can
work out.
Jacob
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