Django：根据字段状态注释总和案例 [英] Django: annotate Sum Case When depending on the status of a field

问题描述

在我的应用程序中，我需要获取过去30天每天的所有交易。

In my application i need to get all transactions per day for the last 30 days.

在交易模型中，我有一个货币字段，如果选择的货币是GBP或USD，我想将其转换为欧元。

In transactions model i have a currency field and i want to convert the value in euro if the chosen currency is GBP or USD.

models.py

models.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)

直到现在这是我一直在使用的：

Until now this is what i've been using:

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

包含日期和金额的字典的查询集：

which returns a queryset containing dictionaries with date and amount:

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

这就是我现在尝试的内容：

and this is what i tried now:

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()))
)

这会将gbp或usd转换为欧元，但它会在同一天创建3个字典，而不是求和

which is converting gbp or usd to euro but it creates 3 dictionaries with the same day instead of making the sum of them.

这是返回的内容：< 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 =< UT C>），金额：25.0}]>

这就是我想要的：

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

推荐答案

唯一剩下的就是 order_by 。这将（是的，我知道这听起来很奇怪），迫使Django执行 GROUP BY 。因此应将其重写为：

The only thing that remains is an order_by. This will (yeah, I know that sounds strange), force Django to perform a GROUP BY. So it should be rewritten to:

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()
    ))
).order_by('date')

（我在这里固定了一些格式设置，以使其更易读，尤其是对于小屏幕，但是（如果忽略间距）与问题中的相同，除了 .order_by（..） 当然。）

(I here fixed the formatting a bit to make it more readable, especially for small screens, but it is (if we ignore spacing) the same as in the question, except for .order_by(..) of course.)

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