how to write a use defined function inside django models.py?

Question

I had written a function inside models.py which will calculate percentage. But it not showing the calculated values.

I have written a function called 'cal_amount' in models.py performed the calculation. return the value to the model field. But it showing None when i called.

class Course(models.Model):
        price = models.FloatField("Price", blank=True, null=True)
        voucher_id = models.CharField(max_length=255,blank=True, null=True)
        voucher_amount = models.IntegerField(blank=True, null=True)
        discounted_amount = models.IntegerField(blank=True, null=True)
        def __str__(self):  
            return self.course_name

        def cal_amount(self):
             self.discounted_amount = (self.voucher_amount/100)*self.price
             return self.discounted_amount

What i want is calculated amount to be stored in discounted_amount. so i can use {{ obj.discounted_amount }} in html to view it along with actual price. Please suggest me a way.

thanks for the reply. you mean like this? data = Course.objects.get(course_name=self.course_name) data.discounted_amount = self.discounted_amount data.save() — Saran Prasad
– Saran Prasad, Commented Apr 25, 2019 at 7:35
data = Course.objects.get(course_name=self.course_name) after this data. cal_amount() and then data.save() — Max
– Max, Commented Apr 25, 2019 at 8:15
Why do you want to save this to a field? Just calling a method which returns this calculation when required seems like it would be fine. — Daniel Roseman
– Daniel Roseman, Commented Apr 25, 2019 at 8:17

grouchoboy · Accepted Answer · 2019-04-25 08:21:35Z

1

Instead of a field in the model, you can use a property.

class Course(models.Model):
        price = models.FloatField("Price", blank=True, null=True)
        voucher_id = models.CharField(max_length=255,blank=True, null=True)
        voucher_amount = models.IntegerField(blank=True, null=True)

        def __str__(self):  
            return self.course_name

        @property
        def discounted_amount(self):
             return (self.voucher_amount/100)*self.price


course = Course.objects.get(id=1)
course.discounted_amount # returns the calculated discount

Keep in mind that you are mixing integers with floats to do the calculation

answered Apr 25, 2019 at 8:21

grouchoboy

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