如何在Django中汇总模型的所有实例

Question

这些是我的模特

class Countries(models.Model):
    Name = models.CharField(max_length=100)
    Language = models.IntegerField()
    Population = models.IntegerField(default=0)

class World(models.Model):
    Languages_spoken = model.Charfield(max_length=12000)
    World_population = models.IntegerField(default=0)

我正在尝试添加“ Countries中所有实例的“ Population ， World_population和并在“ World ”类的“ World World_population字段中显示

我尝试过的

class World(models.Model):
    Languages_spoken = model.Charfield(max_length=12000)
    World_population = models.IntegerField(default=0)
    def save(self, *args, **kwargs):
        self.World_population = Countries.objects.get(Population) # I know this is not correct
        super(World,self).save()

Answer 1

试一下：

from django.db.models import Sum
Countries.objects.aggregate(total_population=Sum('Population'))

有关聚合的更多信息，请点击此处

Answer 2

您可以在此处使用Sum（），

self.World_population = Countries.objects.aggregate(Sum('Population'))

https://docs.djangoproject.com/en/2.1/topics/db/aggregation/