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) 

Answer 2

Justin Hamades answer

class PO(models.Model)     qty = models.IntegerField(null=True)     cost = models.IntegerField(null=True)      @property     def total(self):         return self.qty * self.cost