如何在 django 模型中计算@property 函数的总和？

Question

我想计算total_amount 属性的总和。这是我的models.py

class Orders(models.Model):
    order_id = models.AutoField(primary_key=True)
    order_item = models.ForeignKey('Product', models.DO_NOTHING, db_column='order_item', blank=True, null=True,
        related_name='ordered_item')
    order_status = models.CharField(max_length=100, blank=True, null=True)
    delivery_address = models.TextField(blank=True, null=True)
    customer = models.ForeignKey('User', models.DO_NOTHING, db_column='customer', blank=True, null=True)
    quantity = models.IntegerField()
    date_time = models.DateTimeField()
  
    
    @property
    def total_amount(self):
        rate = Product.objects.get(pk=self.order_item.product_id)
        total_amount = rate.price * self.quantity
        return total_amount

    @property
    def unit_rate(self):
        rate = Product.objects.get(pk=self.order_item.product_id)
        return rate.price

Answer 1

你不需要一个属性方法。而是像这样使用annotate：

from django.db.models import Sum, F, ExpressionWrapper, DecimalField

Orders.objects.filter(date_time__month=6).annotate(
    total_amount = ExpressionWrapper(
        F('order_item__price')*F('quantity'),
        output_field=DecimalField()
    )
).aggregate(monthly_total=Sum('total_amount'))['monthly_total']