Question

I’m trying to do something like that:

class PollResults(models.Model):
    votes_0 = models.IntegerField( default=0 )
    votes_1 = models.IntegerField( default=0 )
    votes_2 = models.IntegerField( default=0 )
    votes_3 = models.IntegerField( default=0 )
    votes = [votes_0,votes_1,votes_2,votes_3]

    def add_vote(self,choice):
        self.votes[choice] = self.votes[choice]+1

But, when I call add_vote(0), I am getting: “unsupported operand type(s) for +: ‘IntegerField’ and ‘int'”.

Is there any way to make it working? Please don’t criticize the database design, this is just an example. The point is how to get/set the field value.

Answer 1

The reason it doesn’t work is because you are referring to field objects themselves in your votes variable. Your code is doing the same thing as models.IntegerField(default=0) + 1 which is of course invalid.

The simplest solution is to simply get/set new attributes and let the django magic deal with the fields -> value conversions.

def add_vote(self,choice):
    attname = 'votes_{0}'.format(choice) # get the attribute name
    value = getattr(self, attname) # get the value
    setattr(self, attname, value+1) # set the value

If you want to use this votes field of yours to determine index / field, you can access Field.attname to figure out the attribute name of your field.

def add_vote(self,choice):
    attname = self.votes[choice].attname
    value = getattr(self, attname) # get the value
    setattr(self, attname, value+1) # set the value