如何在Django中匯總模型的所有實例

Question

這些是我的模特

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)

我正在嘗試添加“ Countries中所有實例的“ Population ， World_population和並在“ World ”類的“ World World_population字段中顯示

我嘗試過的

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

試一下：

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

有關聚合的更多信息，請點擊此處

Answer 2

您可以在此處使用Sum（），

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

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