i do not know if is database killing or not, but you could try some of those
Person.objects.select_related(depth=2).get()
or you could make something like
Membership.objects.select_related(depth=1).get()
That will perform a query on the entire membership table and related
tables in order to extract the values
but you could try something like
Membership.objects.distinct('person_id').select_related(depth=1).get()
Alecs
On Mon, Sep 14, 2009 at 11:27 PM, W.P. McNeill <bill...@gmail.com> wrote:
>
> Never mind. Tiago Serafim's reply answered my question for me.
>
> Follow on question: say I want to make a 2-dimensional table of the
> dates when people joined bands. I'd have code that looks like this.
>
> for p in Person.objects.all():
> for g in Group.objects.all():
> date = Membership.objects.get(person=p, group=g).join_date
> ...
>
> Am I making (person x group) database calls here? This is impression
> I get from reading:
>
> http://docs.djangoproject.com/en/dev/ref/models/querysets/#id1
>
> Is this inefficient? Is there a way to do this with a single database
> call?
>
>
> On Sep 14, 11:43 am, "W.P. McNeill" <bill...@gmail.com> wrote:
> > Or maybe another way of asking this, since I don't want to force you
> > to write Python code just to answer my question...
> >
> > If I have the music group model written as shown in the Django
> > documentation is it possible to write a model API statement that gets
> > me this information, or would I have to add fields to the model?
> >
> > Thanks.
> >
> > On Sep 14, 9:46 am, Alexandru-Emil Lupu <gang.al...@gmail.com> wrote:
> >
> >
> >
> > > basically you would have to make a ManyToMany relation thru a class. In
> that
> > > class you make m,n,date field
> > > After that you just use a query to answer the question: Who (Paul)?
> joined
> > > to whom (Beatles), and after that will pop up the ManyToMany date field
> that
> > > will answer to question "when".
> >
> > > I am preety new in django my self .. and i don't know pretty well how
> to do
> > > it...
> >
> > > On Mon, Sep 14, 2009 at 6:21 PM, W.P. McNeill <bill...@gmail.com>
> wrote:
> >
> > > > I can't figure out how to query the values of fields in a ManyToMany
> > > > "through" table.
> >
> > > > For instance, say I'm working with the Beatles database in the Django
> > > > documentation (
> http://docs.djangoproject.com/en/dev/topics/db/models/
> > > > #extra-fields-on-many-to-many-relationships<
> http://docs.djangoproject.com/en/dev/topics/db/models/%0A#extra-field..
> .>).
> > > > I want to be able to
> > > > query the date on which Paul joined the Beatles. (As opposed to when
> > > > Ringo joined the Beatles, or when Paul joined Wings.) Basically I
> > > > want to treat the Group table as a two-dimensional array, look up:
> >
> > > > Group[Beatles][Paul].date_joined
> >
> > > > and have it return:
> >
> > > > date(1960, 8, 1)
> >
> > > > I'd think this would be easy to do, but I've been playing around with
> > > > the command-line database API and I can't figure it out. The
> > > > documentation I've seen describes how to use a Membership field as a
> > > > filter criteria, but not how to look up the actual value.
> >
> > > --
> > > As programmers create bigger & better idiot proof programs, so the
> universe
> > > creates bigger & better idiots!
> > > I am on web: http://www.alecslupu.ro/
> > > I am on twitter:http://twitter.com/alecslupu
> > > I am on linkedIn:http://www.linkedin.com/in/alecslupu
> > > Tel: (+4)0748.543.798
> >
>
--
As programmers create bigger & better idiot proof programs, so the universe
creates bigger & better idiots!
I am on web: http://www.alecslupu.ro/
I am on twitter: http://twitter.com/alecslupu
I am on linkedIn: http://www.linkedin.com/in/alecslupu
Tel: (+4)0748.543.798
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