How to add a calculation in Django model? - django

Question

I just want to be Per Amount to Paid Amount and result will be posted in balance automatic
this is my admin.py
#admin.register(StudentPaymentSchedules)
class StudentPaymentSchedulesAdmin(admin.ModelAdmin):
list_display = ('Fullname','Grade_Level','Payment_Schedule','Amount','Student_Payment_Date','Paid_Amount','Balance','Remarks',)
ordering = ('pk','Students_Enrollment_Records__Education_Levels')
search_fields = ('Students_Enrollment_Records__Student_Users__Firstname','Students_Enrollment_Records__Student_Users__Lastname',)
list_filter = ('Students_Enrollment_Records__Education_Levels',)
def Fullname(self, obj):
return obj.Students_Enrollment_Records.Student_Users
def Grade_Level(self, obj):
return obj.Students_Enrollment_Records.Education_Levels
actions = ["export_as_csv"]
def export_as_csv(self, request, queryset):
meta = self.model._meta
field_names = [field.name for field in meta.fields]
response = HttpResponse(content_type='text/csv')
response['Content-Disposition'] = 'attachment; filename={}.csv'.format(meta)
writer = csv.writer(response)
writer.writerow(field_names)
for obj in queryset:
row = writer.writerow([getattr(obj, field) for field in field_names])
return response
I have this models.py
class StudentPaymentSchedules(models.Model):
Students_Enrollment_Records=models.ForeignKey(StudentsEnrollmentRecord, related_name='+', on_delete=models.CASCADE,null=True,blank=True)
Payment_Schedule =models.CharField(max_length=500,null=True,blank=True)
Amount = models.FloatField(null=True,blank=True)
Student_Payment_Date = models.DateField(null=True, blank=True)
Paid_Amount = models.FloatField(null=True,blank=True)
Balance = models.FloatField(null=True,blank=True)
Remarks=models.TextField(max_length=500,null=True,blank=True)
for example if the Amount is 1,950 and the Paid Amount is 1500 if the admin click the Save button it will cocompute.

Answer 1

you can use pre-save signals to do it.
from django.db.models.signals import pre_save
def balance_reciever(sender, instance, *args, **kwargs):
Amount = instance.Amount
Paid_Amount = instance.Paid_Amount
Balance = Amount-Paid_Amount
instance.Balance = Balance
pre_save.connect(balance_reciever, sender=StudentPaymentSchedules)

Answer 2

You can use Django Admin save_model but I think you shouldn't create a separate column for a division result. Instead you should use #property function in your model class like this:
class StudentPaymentSchedules(models.Model):
Students_Enrollment_Records=models.ForeignKey(StudentsEnrollmentRecord, related_name='+', on_delete=models.CASCADE,null=True,blank=True)
Payment_Schedule =models.CharField(max_length=500,null=True,blank=True)
Amount = models.FloatField(null=True,blank=True)
Student_Payment_Date = models.DateField(null=True, blank=True)
Paid_Amount = models.FloatField(null=True,blank=True)
Remarks=models.TextField(max_length=500,null=True,blank=True
#property
def balance(self):
return self.Amount - self.Paid_Amount
And use SQL divide function if you need to get data directly from database.