I am creating these models. I want to put toy into bags.

class Bag(models.Model):
    name = models.charField()

    @classmethod
    def calculate_total_weight(cls, bag_id):
        total_weight = 0
        toys_in_bag = Toy.objects.filter(bag_id=bag_id)
        for toy in toys_in_bag:
            total_weight += toy.weight
        return total_weight

class Toy(models.Model):
    bag = models.ForeignKey(Bag, on_delete=models.CASCADE)
    weight = models.IntegerField()

So here’s the problem. Toy belongs to bags, so toy has a foreign key pointing to Bag, so class Bag should be defined first. So when declearing class function calculate_total_weight , class toy is not available yet.

for this specific problem, after searching I got a workaround: apps.get_model

from django.apps import apps
toy = apps.get_model('santa_gift','Toy')

but for other senario, how to tackle this issue?