title: Accessing propertis of OneToOneFiled in the Same model
body: <p>In the below example I'm trying to make default amount on the receipt the total method of related model bill. Django throws an error. Is there a way to do this?</p>
  
  <pre><code>class Bill(models.Model):
      amount1 = models.DecimalField(max_digits = 11, decimal_places = 2, default=0)
      amount2 = models.DecimalField(max_digits = 11, decimal_places = 2, default=0)
  
      def total_amount(self):
          return (self.amount1+self.amount2)
  
  
  
  class Receipt(models.Model):
      bill = models.OneToOneField(Bill, on_delete=models.CASCADE)
      amount = models.DecimalField(max_digits = 11, decimal_places = 2, default=bill.total)
  </code></pre>