获取每个订单行的可退款项目总数

Question

我正在尝试获取仍可退款的特定订单的剩余 OrderLines。

因此，对于 Order 的每个 OrderLine，我想计算引用 Orderline 的所有现有 RefundedLine 的 number 属性的总和。

然后将此总和与 OrderLine 编号 属性进行比较：如果相等，则无法再退款，如果小于则可以退款 (sum(RefundedLine number) < OrderLine number)。

（可以有多个 RefundedLine 引用一个 OrderLine，因为一个订单可以有单独的 Refund，直到全额退款）。

这是我的模型：

class Order(models.Model):
    pass

class OrderLine(models.Model):
    order = models.ForeignKey(Order,
                              on_delete=models.CASCADE,
                              related_name="order_lines")
    number = models.SmallIntegerField(default=1,
                                      validators=[MinValueValidator(1)])

class Refund(models.Model):
    """ Is attached to one order, can concern multiples lines """
    order = models.ForeignKey(Order, on_delete=models.PROTECT, editable=False)
    lines = models.ManyToManyField(OrderLine, through='RefundedLine')

class RefundedLine(models.Model):
    """ Used for m2m """
    refund = models.ForeignKey(Refund, on_delete=models.CASCADE)
    line = models.ForeignKey(OrderLine, on_delete=models.PROTECT)
    number = models.SmallIntegerField(default=1,
                                      validators=[MinValueValidator(1)])

---

现在我的尝试和他们的错误：

尝试 1：

return OrderLine.objects.filter(order=self.order_id,
                                        number__lt=Sum(Subquery(
                                            RefundedLine.objects.filter(line=OuterRef('pk')).values('number')
                                        )))

错误：列 « cart_orderline.id » 必须出现在 GROUP BY 子句中或必须在聚合函数中使用 第 1 行：选择 "cart_orderline"."id", "cart_orderline"."order_id", "...

错误信息不准确，我自己翻译的

尝试 2：

From the Django doc itself，没有错误但无法按预期工作。如果 OrderLine 没有引用它的 RefundedLine，我会得到一个空查询集，而它应该返回 OrderLine。

refunded_lines = RefundedLine.objects.filter(line=OuterRef('pk')).order_by().values('line')
        total_refunded_lines = refunded_lines.annotate(total=Sum('number')).values('total')
        refundable_lines = OrderLine.objects.filter(number__gt=Subquery(total_refunded_lines))

尝试 3：

refunded_lines = RefundedLine.objects.filter(line=OuterRef('pk')).order_by().values('line')
        total_refunded_lines = refunded_lines.annotate(total=Sum('number', output_field=models.IntegerField())).values('total')
        refundable_lines = OrderLine.objects\
            .filter(order=self.order_id)\
            .annotate(refundable_number=Case(
            When(
                Exists(total_refunded_lines),
                then=Value(total_refunded_lines[:1]),
            ),
            default=Value(0),
            output_field=models.IntegerField()
        )).filter(refundable_number__gt=0)

错误信息：

django.db.utils.ProgrammingError: can't adapt type 'QuerySet'

当我尝试遍历refunded_lines。

---

我还有其他尝试，但我认为写它们不会有好处，因为帖子已经很混乱了。

Answer 1

尝试以下方法：

from django.db.models import Sum, F
OrderLine.objects.filter(
   # do your filtering here if you do not need the annotated value
).annotate(
    refunded_number=Coalesce(Sum('refundedline__number'),0)  # Annotate each OrderLine with the sum of the numbers of its refundedline
).filter(
    number__gt=F('refunded_number')  # Use F() objects to reference a field
)

Answer 2

感谢@GrandPhuba，我可以测试并完成他的答案

# Added the missing filter for the order
refundable_lines= OrderLine.objects.filter(order=self.order_id).annotate(
            # Added Coalesce because if no refundedline exist for the orderline, None will be returned and so the QuerySet will be empty, we do not want that
            refunded_number=Coalesce(Sum('refundedline__number'), 0) 
            # Annotate each OrderLine with the sum of the numbers of its refundedline
        ).filter(
            number__gt=F('refunded_number'),  # Use F() objects to reference a field
        )