[Fixed]-How to delete an record from Django model

To delete the customer when you delete a calculation:

def delete(self, *args, **kwargs):
    self.customer.delete()
    super(Calculations, self).delete(*args, **kwargs)

To avoid deleting the calculation when you delete a customer:

customer = models.ForeignKey(to=Customer, null=True, blank=True, on_delete=models.SET_NULL)