CODEWITHSUNDEEP
pythondjangodatetimedjango-models
Neighlyd
Neighlyd

Reputation: 352

Django datetime comparison not working as expected in save

I have a custom save routine in one of my models that compares datetime fields and then is supposed to modify a field on another model and save it based on the results. However, the comparison is not working as I would expect it to. Namely, my <= comparison is returning True regardless of the actual comparison.

models.py

class Session(models.Model):
    date = models.DateField()
    # etc...

class Case(models.Model):
    summary = models.TextField(blank=True)
    session = models.ForeignKey(Session, on_delete=models.CASCADE, related_name='cases')
    case_type = models.ForeignKey(CaseType)
    # etc...

class Person(models.Model):
    earliest_case = models.ForeignKey('Case', null=True, blank=True, related_name='person_to_earliest_case+')
    latest_case = models.ForeignKey('Case', null=True, blank=True, related_name='person_to_latest_case+')
    # etc...


class Litigant(models.Model):

    person = models.ForeignKey(Person, on_delete=models.CASCADE, related_name='person_to_case')
    case = models.ForeignKey(Case, on_delete=models.CASCADE, related_name='case_to_person')
    # etc...

    def save(self, *args, **kwargs):
         try:
             person = Person.objects.get(id=self.person_id)
             earliest_case = person.earliest_case
             latest_case = person.latest_case
             if self.case.session.date <= earliest_case.session.date:
                  person.earliest_case = self.case
                  person.save()
             elif self.case.session.date >= latest_case.session.date:
                  person.earliest_case = self.case
                  person.save()
         except:
             pass
         super(Litigant, self).save(*args, **kwargs)

As you can see, when I save a new Litigant, what I want it to do is call up the existing Person instance, compare that instance's entries for earliest_case and latest_case with the new Case instance tied to Litigant and then reassign the fields if necessary.

What is happen instead is that the new case is being added to person.earliest_case regardless of whether it is earlier or later than the existing date there, and I'm not really sure why.

For reference, the dates stored in the Session date field are all Year-Date-Month.

Frustratingly, if I call up two instances of case.session.date in the shell, they compare just fine.

If it matters, the case fk is getting added by my view like so:

views.py

def add_litigant(request, pk):
     case_instance = get_object_or_404(models.Case, pk=pk)
     if request.method == "POST":
         form = forms.LitigantForm(request.POST)
         if form.is_valid():
             new_litigant = form.save(commit=False)
             new_litigant.case = case_instance
             new_litigant.save()
     # etc...

# def edit_litigant works the same way

I would appreciate any guidance or pointers. Thanks in advance!

Upvotes: 0

Views: 98

Answers (1)

kszl
kszl

Reputation: 1213

What is happen instead is that the new case is being added to person.earliest_case regardless of whether it is earlier or later than the existing date there, and I'm not really sure why.

That's why:

if self.case.session.date <= earliest_case.session.date:
    person.earliest_case = self.case  # <- assigned to earliest_case
    person.save()
elif self.case.session.date >= latest_case.session.date:
    person.earliest_case = self.case   # <- assigned to earliest_case. COPYPASTA!
    person.save()

Upvotes: 2

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