Python 按分组并使用嵌套字段聚合
我想使用嵌套的序列化器字段分组,并在其他字段上计算一些聚合函数 我的模型课程:Python 按分组并使用嵌套字段聚合,python,django,django-rest-framework,Python,Django,Django Rest Framework,我想使用嵌套的序列化器字段分组,并在其他字段上计算一些聚合函数 我的模型课程: class Country(models.Model): code = models.CharField(max_length=5, unique=True) name = models.CharField(max_length=50) class Trade(models.Model): country = models.ForeignKey( Country, null=
class Country(models.Model):
code = models.CharField(max_length=5, unique=True)
name = models.CharField(max_length=50)
class Trade(models.Model):
country = models.ForeignKey(
Country, null=True, blank=True, on_delete=models.SET_NULL)
date = models.DateField(auto_now=False, auto_now_add=False)
exports = models.DecimalField(max_digits=15, decimal_places=2, default=0)
imports = models.DecimalField(max_digits=15, decimal_places=2, default=0)
我的序列化程序类:
class CountrySerializers(serializers.ModelSerializer):
class Meta:
model = Country
fields = '__all__'
class TradeAggregateSerializers(serializers.ModelSerializer):
country = CountrySerializers(read_only=True)
value = serializers.DecimalField(max_digits=10, decimal_places=2)
class Meta:
model = Trade
fields = ('country','value')
我想发送import或export作为查询参数,并对其应用聚合(avg),由不同的国家显示
我的观点类:
class TradeAggragateViewSet(viewsets.ModelViewSet):
queryset = Trade.objects.all()
serializer_class = TradeAggregateSerializers
def get_queryset(self):
import_or_export = self.request.GET.get('data_type')
queryset = self.queryset.values('country').annotate(value = models.Avg(import_or_export))
return queryset
我希望以如下格式获取数据:
[
{
country:{
id: ...,
code: ...,
name: ...,
},
value:...
},
...
]
但在国家/地区序列化程序上出错
AttributeError: Got AttributeError when attempting to get a value for field `code` on serializer `CountrySerializers`.
The serializer field might be named incorrectly and not match any attribute or key on the `int` instance.
Original exception text was: 'int' object has no attribute 'code'.
我找到了解决办法。实际上,serializer类中的to_表示只获取了国家的id,而不是其对象,因此我重写to_表示为:
class TradeAggregateSerializers(serializers.ModelSerializer):
...
...
def to_representation(self, instance):
#instance['country'] = some id, not object
#getting actual object
country = Country.objects.get(id=instance['country'])
instance['country'] = country
data = super(TradeAggregateSerializers, self).to_representation(instance)
return data
Django查询集没有
值
属性。将其更改为:queryset=self.queryset.values('country')。注释(value=models.Avg(导入或导出))