va:patrick.kranzlmueller wrote:
> I have a model with blog-postings, assigned to a specific user - the
> user is stored in the table "posting" via foreignkey.
>
> the user is part of a grade, part of a school and part of a state -
> all of which have overview-pages.
> so, to get all the postings for a state I have to do the following:
>
> 1. search for schools in that state
> 2. search for grades in that school
> 3. search for users within that grade
> 4. and finally, get all the postings for that user
>
> seems a little complicated.
Not sure if I understand your models exactly, but you don't need to do
four "searches" (queries), you just need to do one query with the
constraint that spans the four relations. Assuming your models look
something like this:
class State(models.Model):
code = models.CharField(maxlength=2)
class School(models.Model):
state = models.ForeignKey(State)
class Grade(models.Model):
school = models.ForeignKey(School)
class User(models.Model):
grade = models.ForeignKey(Grade)
class Posting(models.Model):
user = models.ForeignKey(User)
Then you can just do this to find all postings for users in grades in
schools in New York:
Posting.objects.filter(user__grade__school__state__code='NY')
Which will translate into one query looking something like this:
select * from posting
join user on posting.user_id = user.id
join grade on user.grade_id = grade.id
join school on grade.school_id = school.id
join state on school.state_id = state.id
where state.code = 'NY'
(abbreviated - the actual Django version of the SQL will be quite a bit
more verbose due to fully qualified column names).
Of course, I may have completely misunderstood your models and this may
be completely off base!
-Dave
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