Question

我有这个Django模型：

class Location(models.Model):
    name = models.CharField(primary_key=True, max_length=100)
    customer = models.OneToOneField(Customer, default=None)

class Customer(models.Model):
    name = models.CharField(primary_key=True, max_length=100)

class Order(models.Model):
    amount = models.PositiveIntegerField(default=0)
    customer = models.ForeignKey(Customer, default=0)

在我看来，我得到这样的话：

locations = models.Location.objects.all()

，模板将它们列为：

{% for location in locations %}
    {{ location.customer.name }}
{% endfor %}

我想添加与该客户相关的所有amount的所有Order的总和，如：

{% for location in locations %}
    {{ location.customer.name }} ordered {{ location.customer.orders.sum(amount) }} items
{% endfor %}

根据this question，我应该在视图中这样做，但是如何？

Answer 1

您应该使用.annotate（look in docs）：

from django.db.models import Count

customers = models.Customer.objects.annotate(orders_count=Count('order'))

然后在模板中你可以像这样使用它：

{% for customer in customers %}
    {{ customer.name }} ordered {{ customer.orders_count }} items
{% endfor %}

Answer 2

经过一番徘徊，我发现这有效：

locations = models.Location.objects.annotate(num_order=Count('customer__order'))

然后在模板中使用它：

{% for location in locations %}
    {{ location.customer.name }} ordered {{ location.num_order }} items
{% endfor %}

在模板中获取聚合

2 个答案: