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
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