python - Create a field whose value is a calculation of other fields' values

Question

class PO(models.Model)
    qty = models.IntegerField(null=True)
    cost = models.IntegerField(null=True)
    total = qty * cost

How will I solve total = qty * cost above. I know it will cause an error, but have no idea of how to deal with this.

Answer 1

You can make total a property field, see the docs

class PO(models.Model)
    qty = models.IntegerField(null=True)
    cost = models.IntegerField(null=True)

    def _get_total(self):
       "Returns the total"
       return self.qty * self.cost
    total = property(_get_total)