在Django的查询集中总结一个字段

Posted 2023-02-24

【中文标题】在Django的查询集中总结一个字段

【英文标题】：Sum up a field in the queryset in Django

【发布时间】：2019-01-04 09:03:48

【问题描述】：

models.py

class QaCommission(models.Model):
    user = models.ForeignKey(PlUser, on_delete=models.CASCADE, blank=True, null=True, related_name='user_commission')
    ref = models.ForeignKey(PlUser, on_delete=models.CASCADE, blank=True, null=True, related_name='ref_commission')
    price = models.FloatField(blank=True, null=True)
    pct = models.FloatField(blank=True, null=True)
    commission = models.FloatField(blank=True, null=True)
    status = models.IntegerField(blank=True, null=True, default=0)

序列化器.py

class QaCommissionSerializer(serializers.ModelSerializer):
    class Meta:
        model = QaCommission
        fields = '__all__'

views.py

class QaCommissionList(viewsets.ModelViewSet):
    queryset = QaCommission.objects.all()
    serializer_class = QaCommissionSerializer

如果我们在此视图中过​​滤 ref=60，结果显示如下：

"count": 18,
"next": "http://127.0.0.1:8008/api/qacommission/?ref=60&page=2",
"previous": null,
"results": [
    
        "id": 1,
        "price": 20.0,
        "pct": 0.1,
        "commission": 2.0,
        "status": 1,
        "user": 7,
        "ref": 60
    ,
    
        "id": 2,
        "price": 10.0,
        "pct": 0.1,
        "commission": 1.0,
        "status": 1,
        "user": 7,
        "ref": 60
    ,
    ......
    ......
    ......
    
        "id": 10,
        "price": 15.0,
        "pct": 0.1,
        "commission": 1.5,
        "status": 1,
        "user": 7,
        "ref": 60
    
]

我想对结果中的所有“commission”字段求和，并将总和附加到原始查询集（可能在“count”旁边：18），如上图，有18个commission需要计算。

我该如何实现呢？需要您的帮助，谢谢！

【问题讨论】：

from django.db.models import Sum \n qs = QaCommission.objects.filter().aggregate(commission_sum=Sum('commission')) sum is stored in qs['commission_sum']

也许这个https://***.com/questions/31920853/aggregate-and-other-annotated-fields-in-django-rest-framework-serializers会回答你的问题

在模型类中添加类方法可以帮助你总结出你的queryset结果的commision值。

【参考方案1】：

尝试覆盖ModelViewset的list()方法为，

class QaCommissionList(viewsets.ModelViewSet):
    queryset = QaCommission.objects.all()
    serializer_class = QaCommissionSerializer

    def list(self, request, *args, **kwargs):
        response = super().list(request, *args, **kwargs)
        response.data['sum'] = sum([data.get('commission', 0) for data in response.data['results']])
        return response

这个答案总结了commision 来自特定页面并显示它 更新

from django.db.models import Sum


class QaCommissionList(viewsets.ModelViewSet):
    queryset = QaCommission.objects.all()
    serializer_class = QaCommissionSerializer

    def list(self, request, *args, **kwargs):
        response = super().list(request, *args, **kwargs)
        if 'ref' in request.GET and request.GET['ref']:
            response.data['sum'] = QaCommission.objects.filter(ref=int(request.GET['ref'])
                                                               ).aggregate(sum=Sum('commission'))['sum']
        return response

上面的答案将返回 commission 列 w.r.t 的整数和过滤器（不考虑分页） 感谢@bruno 提到这样一个有效的观点

【讨论】：

不使用SQL数据库有什么意义？

我认为他需要，sum(commission)来自当前页面

很棒的答案！我需要所有页面的总和，但我也从当前的第一页中受益。谢谢！