After a preliminary reading of your answer, the second solution seems
like what I am trying to do. Basically this is a simple Track and
Field competition manager, and one year a student will compete as a
midget and get a result for the 100m dash, and the next year compete
as a junior and get a result for the 100m dash.
Thank you for your time and effort.
On Jan 22, 5:15 pm, Russell Keith-Magee <freakboy3...@gmail.com>
wrote:
> On Thu, Jan 22, 2009 at 10:57 PM, jason.t.stein <jason.t.st...@gmail.com>
> wrote:
>
> > Perhaps this is an sql question, and not a Django question so please
> > have patience. I am writing a student management app that keeps track
> > of student events. The relevant tables are:
>
> > class Student(models.Model):
> > first_name = models.CharField(max_length=32)
> > last_name = models.CharField(max_length=32)
> > birth_date = models.DateField('Student Birth Date')
> > gender = models.CharField(max_length=1, choices = GENDER_CHOICES)
> > school = models.ForeignKey(School)
>
> > class Competitor(models.Model):
> > student = models.ForeignKey(Student)
> > track_meet = models.ForeignKey(TrackMeet)
> > age_category = models.CharField(max_length=1, choices =
> > AGE_CATEGORY_CHOICES)
> > event = models.CharField(max_length=16, choices = EVENT_CHOICES)
>
> > I want to set age_category, based on the age of a student on a certain
> > date. I can calculate the appropriate age, but am interested how to
> > set the age_category based on this calculation.
>
> > Any help is greatly appreciated. Thank you for your time.
>
> Hi Jason,
>
> There are several possible answers to your question, depending on how
> and when you want to set the age_category.
>
> Are you looking to do this as a bulk SQL operation (i.e., update every
> object at once)? In which case, the best way will be in raw SQL - you
> will need to investigate the CASE operator on your database of choice.
>
> Alternatively, if you are looking to set the initial age category when
> the competitor record is saved to the database, then all you need to
> do is override the save() method on your competitor. The following
> code is untested (and not particularly accurate as an age
> calculation), but should give you an idea of the approach:
>
> def save(self, *args, **kwargs):
> age = (date.today() - self.student.birth_date) / 365
> if age > 10:
> self.age_category = AGE_CATEGORY.SENIOR
> else:
> self.age_category = AGE_CATEGORY.JUNIOR
> super(Competitor, self).save(*args, **kwargs)
>
> It's also worth asking whether the age category needs to be in the
> database at all. If it is purely derived from the age of the student,
> there may be an argument for not storing it in the database at all,
> and computing the age category whenever it is required.
>
> Hope this helps,
>
> Yours,
> Russ Magee %-)
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