#3587: filter() and order_by()
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Reporter: [EMAIL PROTECTED] | Owner: adrian
Status: new | Component: Database wrapper
Version: 0.95 | Resolution:
Keywords: | Stage: Unreviewed
Has_patch: 0 | Needs_docs: 0
Needs_tests: 0 | Needs_better_patch: 0
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Comment (by [EMAIL PROTECTED]):
More readable version of the code follows (sorry about that)
Models :
{{{
class Cadet(models.Model):
sqn = models.ForeignKey?(Squadron)
enrollment_date = models.DateField?(help_text="YYYY-MM-DD")
date_of_birth = models.DateField?(help_text="YYYY-MM-DD")
class Camp(models.Model):
name = models.CharField?(maxlength=40)
min_training_level = models.PositiveIntegerField?("Minimum training
level", default=0)
min_age = models.FloatField?("Minimum age", max_digits=3,
decimal_places=1, default=0)
class Application(models.Model):
cadet = models.ForeignKey?(Cadet, edit_inline=models.STACKED,
num_extra_on_change=1, num_in_admin=1)
year = models.IntegerField?(maxlength=4, core=True, help_text="4-digit
year", validator_list=[year_validator])
camp = models.ForeignKey?(Camp, core=True) training_level =
models.PositiveIntegerField?("current training level")
}}}
Here's the function I ended up with after trying to get it going with
filter() :
{{{
def exception_age(request, year_filter):
"""Lists cadets that might not be the right age for the course they
applied for."""
this_june = date(int(year_filter), 6, 1)
this_sept = date(int(year_filter), 9, 1)
apps = list(Application.objects.filter(year=year_filter))
# filter out any that are definitely the right age
apps = [a for a in apps if (a.cadet.age_on(this_june) <
float(a.camp.min_age)) or (a.cadet.ages_out() < this_sept)]
}}}
I don't have the filter() versions that I tried along the way, but it was
based on comparing the application.cadet.date_of_birth field.
This one involves comparing the values in two tables :
{{{
def exception_eligibility(request, year_filter):
"""Lists cadets not in the right level for the course they applied
for."""
apps = list(Application.objects.filter(year=year_filter))
# filter out any that are in the right level
apps = [a for a in apps if a.training_level <
a.camp.min_training_level]
# Sort the list by squadron number
apps.sort(key=sqn_of_app)
return render_to_response('camps/exception_eligibility.html',
{'object_list' : apps,})
}}}
and this one requires doing a calculation on the difference between two
fields (cadet.date_of_birth and cadet.enrollment_date) :
{{{
def exception_enrollment(request, year_filter):
"""Lists cadets enrolled too young who've applied this year."""
apps = list(Application.objects.filter(year=year_filter))
# filter out any that joined old enough
cdts = [a.cadet for a in apps if a.cadet.age_at_enrollment() < 12]
# Sort the list by squadron number
cdts.sort(key=sqn_of_cdt)
return render_to_response('camps/exception_enrollment.html',
{'object_list' : cdts,})
}}}
As for the dot syntax, http://www.djangoproject.com/documentation/db_api/#
order-by-fields says :
{{{To order by a field in a different table, add the other table's name
and a dot, like so}}}
which lends the idea some legitimacy...
--
Ticket URL: <http://code.djangoproject.com/ticket/3587#comment:5>
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