[Django]-Django. Default value from foreign key

by

1👍

✅

You should override Lot.save to set the default value for price.

class Lot(models.Model):
    item = models.ForeignKey(Item)
    price = models.FloatField()
    ....

    def save(self, *args, **kwargs):
        if not self.price:
            self.price = self.item.price
        super(Lot, self).save(*args, **kwargs)
👤Derek Kwok

2👍

default in your model definition is not ‘instance-aware’. I’d suggest overriding the save method of Lot to pull in price at time of save.

class Lot(models.Model):

    item = models.ForeignKey(Item)
    count = models.IntegerField(default = 1)
    price = models.FloatField(default = item.price) #Price on the moment of buying
    def __str__(self):              # __unicode__ on Python 2
        return self.item.name

    def save(self, *args, **kwargs):
        if self.item: # verify there's a FK
            self.price = self.item.price
        super(Lot, self).save(*args,**kwargs) # invoke the inherited save method; price will now be save if item is not null

    def cost(self):
         return self.price * self.count
👤Ian Price

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