How to refer to a function in a model?

Question

Django

Hello.
Question for the experts. I want to remove a condition from the template into the model.
models.py

master_promo_count = models.SmallIntegerField(default=0, verbose_name='Количество дней акции',)
 # СЧЕТЧИК АКЦИИ
    def promo(self, *args, **kwargs):
        self.master_promo_count = (self.master_date_end - datetime.today().date()).days
        return self.master_promo_count

    # Замена словаря в шаблоне
    def master_promo_count_day(self, *args, **kwargs):
        if self.promo(self, *args, **kwargs) == 1:
            return f'день'
        elif self.promo(self, *args, **kwargs) == 2:
            return f'дня'
        else:
            return f'дней'

html

<span class="red-text bb f18">{{ obj.promo }} {{ obj.master_promo_count_day }}</span></div>

If you do it like this, then everything works.

# Замена словаря в шаблоне
    def master_promo_count_day(self):
        if self.master_promo_count == 1:
            return f'день'
        elif self.master_promo_count == 2:
            return f'дня'
        else:
            return f'дней'

If you access the column to the table, everything works, if the first function does not.
Who will correct what I'm doing wrong?
Thank you.

Answer 1

You generally have a game with the code ...
This is:

master_promo_count = models.SmallIntegerField(default=0, verbose_name='Количество дней акции',)
 # СЧЕТЧИК АКЦИИ
    def promo(self, *args, **kwargs):
        self.master_promo_count = (self.master_date_end - datetime.today().date()).days
        return self.master_promo_count

easily changed to this:

@property
def master_promo_count(self):
      return (self.master_date_end - datetime.today().date()).days

And then this will work:

def master_promo_count_day(self):
        if self.master_promo_count == 1:
            return f'день'
        elif self.master_promo_count == 2:
            return f'дня'
        else:
            return f'дней'

And generally this:

<span class="red-text bb f18">{{ obj.promo }} {{ obj.master_promo_count_day }}</span></div>

like master_promo_count_day - in general, it is better to do it through templatetags if the regular pluralize does not fit