Hi!
How should i get the details from B and some content of A using that
foreign key?
Thanks
Madhu
On Saturday, January 31, 2009 10:37:58 PM UTC+5:30, Daniel Roseman wrote:
>
> On Jan 31, 12:27 pm, Markus <mkn...@gmail.com> wrote:
> > Hi
> >
> > just starting to use Django, am stuck with the following problem:
> >
> > Given
> >
> > class A(models.Model):
> > ...some fields...
> >
> > class B(models.Model):
> > A = models.ForeignKey(A)
> > ....some fields...
> >
> > I would like to generate a Queryset that returns values from both
> > tables, ie in SQL
> >
> > SELECT A.field1, A.field2, B.field1, B.field2
> > FROM A, B
> > WHERE A.id = B.A_id AND some filter on A AND .. some further
> > conditions to ensure only one row from table B is matched
> >
> > So far, I found a way to achieve this using the extra operator:
> >
> > A.objects.filter(..some filter on A..).extra(select={'field1': "select
> > B.field1 from B ...", 'field2': 'select B.field2 from B ..."})
> >
> > This quickly becomes clumsy as the number of fields in table B
> > increases. There must be a better way? As I couldnt find anything in
> > the documentation, I would appreciate a nudge in the right direction.
> >
> > Thanks
> > Markus
>
> You haven't explained exactly what you want from B - all the values,
> or just the ones that have values in A, or just the ones for a single
> value of A?
>
> If you just want all the associated B for each value of A, then a
> simple queryset will do the trick.
> qs = A.objects.all()
> for a in qs:
> print a.b_set.all()
>
> You can make this a bit more efficient by calling the initial queryset
> with select_related.
> qs = A.objects.all().select_related()
>
> I would suggest reading the section on related objects again:
> http://docs.djangoproject.com/en/dev/topics/db/queries/#related-objects
> --
> DR.
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