python - Django:根据字段的状态注释 Sum Case When

Question

在我的应用程序中，我需要获取过去 30 天内每天的所有交易。

在交易模型中，我有一个货币字段，如果选择的货币是英镑或美元，我想将值转换为欧元。

模型.py

class Transaction(TimeMixIn):
    COMPLETED = 1
    REJECTED = 2
    TRANSACTION_STATUS = (
        (COMPLETED, _('Completed')),
        (REJECTED, _('Rejected')),
    )

    user = models.ForeignKey(CustomUser)
    status = models.SmallIntegerField(choices=TRANSACTION_STATUS, default=COMPLETED)
    amount = models.DecimalField(default=0, decimal_places=2, max_digits=7)
    currency = models.CharField(max_length=3, choices=Core.CURRENCIES, default=Core.CURRENCY_EUR)

到目前为止，这是我一直在使用的:

Transaction.objects.filter(created__gte=last_month, status=Transaction.COMPLETED)
                        .extra({"date": "date_trunc('day', created)"})
                        .values("date").annotate(amount=Sum("amount"))

返回包含日期和数量的字典的查询集:

<QuerySet [{'date': datetime.datetime(2018, 6, 19, 0, 0, tzinfo=<UTC>), 'amount': Decimal('75.00')}]>

这就是我现在尝试的:

queryset = Transaction.objects.filter(created__gte=last_month, status=Transaction.COMPLETED).extra({"date": "date_trunc('day', created)"}).values('date').annotate(
    amount=Sum(Case(When(currency=Core.CURRENCY_EUR, then='amount'), 
                    When(currency=Core.CURRENCY_USD, then=F('amount') * 0.8662), 
                    When(currency=Core.CURRENCY_GBP, then=F('amount') * 1.1413), default=0, output_field=FloatField()))
)

它正在将 gbp 或 usd 转换为欧元，但它在同一天创建了 3 个字典，而不是对它们求和。

这是它返回的内容:<QuerySet [{'date': datetime.datetime(2018, 6, 19, 0, 0, tzinfo=<UTC>), 'amount': 21.655}, {'date': datetime.datetime(2018, 6, 19, 0, 0, tzinfo=<UTC>), 'amount': 28.5325}, {'date': datetime.datetime(2018, 6, 19, 0, 0, tzinfo=<UTC>), 'amount': 25.0}]>

这就是我想要的:

<QuerySet [{'date': datetime.datetime(2018, 6, 19, 0, 0, tzinfo=<UTC>), 'amount': 75.1875}]>

Answer 1

唯一剩下的就是 order_by。这将(是的，我知道这听起来很奇怪)强制 Django 执行 GROUP BY。所以应该重写为:

queryset = Transaction.objects.filter(
    created__gte=last_month,
    status=Transaction.COMPLETED
).extra(
    {"date": "date_trunc('day', created)"}
).values(
    'date'
).annotate(
    amount=Sum(Case(
        When(currency=Core.CURRENCY_EUR, then='amount'), 
        When(currency=Core.CURRENCY_USD, then=F('amount') * 0.8662), 
        When(currency=Core.CURRENCY_GBP, then=F('amount') * 1.1413),
        default=0,
        output_field=FloatField()
    ))
)<b>.order_by('date')</b>

(我在这里稍微修正了格式以使其更具可读性，尤其是对于小屏幕，但它(如果我们忽略间距)与问题中的相同，除了 .order_by(..)当然。)