Re: Merging results from two tables
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 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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Re: Merging results from two tables
Thanks, that did the trick!!
On Jan 31, 6:07 pm, Daniel Roseman
wrote:
> On Jan 31, 12:27 pm, Markus 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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Re: Merging results from two tables
On Jan 31, 12:27 pm, Markus 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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Merging results from two tables
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
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"Django users" group.
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