You're right I sniped the date_time field when pasting in the model
after leaving out some extranous detail. Doh!
Ordering by date_time mean't I had duplicates despite grouping by
site. Like you say printing out the query may actually help me
understand what is going on under the hood.
After posting the message, I did a bit more reading I actually used
annotate(last_date=MAX('date_time')) which seems to work reasonably
well and give me the sort of result I was looking for. Again I'll
print the sql for this and see whats going on.
Extending the use case a bit further however what I'd really like to
do is determine how many days have passed since 'last date' and filter
the objects further. It sort of seems as though I'm getting to the
edge of what the ORM is capable of.
>From doing a quick bit of reading it either seems like I'll have to
use the extra() clause or perhaps look at using a property bound to a
method however at this point you're outside the scope of the ORM.
Any ideas on how I can best acheive this?
I'm trying to stay away from using a foreach and looping over a
potentially large number of records and doing this filtering at the DB/
ORM level.
Thanks in advance.
On 5 July, 07:32, "euan.godd...@googlemail.com"
<euan.godd...@gmail.com> wrote:
> Erm. You don't seem to have specified what to order by. In this case,
> surely you want ... .order_by('date_time') However, this field doesn't
> seem to appear in your models.
>
> One thing I've found handy for debugging Django's ORM to SQL is
> something which I don't think is documented in django docs at all
> (although I maybe wrong about that) is doing:
>
> print qs.query
>
> Where qs is your queryset. It will output the SQL Django sends to the
> DB backend.
>
> Euan
>
> On 3 July, 15:03, MikeHowarth <mikehowar...@googlemail.com> wrote:
>
> > Hi all
>
> > Just coming back to Django after a long time away, and struggling to
> > get my head around what should be a trivial concept using the ORM.
>
> > Essentially I want to do acheive the following SQL:
>
> > SELECT * FROM publisher_history
> > INNER JOIN publisher_publisher ON publisher_publisher.id =
> > publisher_history.publisher_id
> > GROUP BY publisher_id ORDER BY date_time DESC;
>
> > My models look like this:
>
> > class Publisher(models.Model):
> > name = models.CharField(max_length=100, blank=False)
>
> > class History(models.Model):
> > publisher = models.ForeignKey(Publisher, blank=False)
>
> > I've been trying to use object values, but I'm getting duplicate
> > publishers. Code looks like this:
>
> > results = History.objects.values('publisher').distinct()
>
> > If I run:
>
> > results = History.objects.values('publisher').distinct().order_by()
>
> > I don't get duplicates but I don't get the results returned in the
> > order I expect either.
>
> > Any help would be greatly appreciated, I've stared at this for a while
> > now.
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