Another thing, which was solved in my group_by patch, is count()'ing
those rows. I haven't looked at any of the aggregate code but did you
solve that?
Here's the query in Curse's ORM:
MyModel.objects.filter(Q(tags__tag='test') |
Q(tags__tag='test2')).extra(having=['count(1) =
2']).group_by('id').count()
On Mar 24, 6:12 pm, "Russell Keith-Magee" <[EMAIL PROTECTED]>
wrote:
> On Mon, Mar 24, 2008 at 7:19 AM, David Cramer <[EMAIL PROTECTED]> wrote:
>
> > So we're not going to support group by at all, even though is
> > extremely simple? I don't understand why everyone says mine (and
> > Curse's and many other peoples) use of SQL is so uncommon. I'd
> > guarantee almost every developer and I know who writes any kind of
> > scalable code (and I've seen what they've written) uses GROUP BY in
> > SQL much more than just for SUM, or COUNT, or any of those operations.
>
> And yet, the example you give is a count on related objects.
>
> > SELECT my_table.* FROM my_table JOIN my_other_table WHERE my_other
> > table.my_table_id = my_table.id GROUP BY my_table.id HAVING COUNT(1) >
> > 1;
>
> > How do you ever hope to achieve something like this in the ORM without
> > patches like mine?
>
> Lets see if I can make myself clearer by using your example.
>
> You have provided some sample SQL. However, that wasn't the start
> point. Once upon a time, you had a problem you needed to solve: "I
> need to find all the MyTable objects that have more than one related
> OtherTable objects". Notice that this question doesn't use the phrase
> "GROUP BY".
>
> Django's ORM didn't support aggregates, so you hand crafted some SQL,
> and since aggregates were involved, you needed to use a GROUP BY
> clause. This is because GROUP BY is the way SQL handles aggregation.
>
> Now, we're talking about adding aggregates to Django. So, we need to
> find a way to express your original question as Django syntax. The
> solution to this problem isn't "add GROUP BY to Django Syntax" - it's
> to find an elegant way to represent the underlying problem as an
> object-based syntax. Based on the discussions so far, something like
> this would seem appropriate:
>
> MyTable.objects.aggregate(othertable__count='related_count').filter(related_count__gt=1)
>
> Notice that this query doesn't require the use of the phrase GROUP BY
> in the ORM syntax. When this hits the database, GROUP BY will
> certainly be required. However, the terms for the GROUP BY can be
> entirely implied from the rest of the query. There is no need to
> expose GROUP BY into the ORM syntax.
>
> Your original question wasn't "How do I perform a GROUP BY over a
> MyTable" - it was a real-world question that needed an object-based
> answer. The goal of the Django ORM is to solve your _actual_ problem,
> not your SQL problem.
>
> > My main argument is there's no reason to *not* include the
> > functionality except that a few select people say "we dont need it".
>
> There is a very good reason, which I have told you several times. The
> Django ORM does not provide an alternate syntax for SQL. It provides a
> way of interrogating an object model that happens to be backed by a
> database. As a result, the external APIs are not SQL specific - they
> encompass broader object-based use-cases. "Just adding GROUP BY"
> doesn't achieve any of the Django design goals.
>
> Now, if you can present a use case that isn't satisfied by the
> discussions we are currently having - that is, a usage of GROUP BY
> that steps outside the bounds of what could be implied from other
> parts of an ORM query - let us know. We want to be able to cover as
> many potential queries as possible. However, even then, I doubt that
> the solution will be "add GROUP BY" - there will be another class of
> object-based queries that we haven't considered, for which we will
> need a new _object based_ syntax.
>
> Yours,
> Russ Magee %-)
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