求和序列化程序Django中的数据

Question

我希望对嵌套对象中的数据求和。

我的型号：

class Diet(models.Model):
day = models.IntegerField()
meals = models.ManyToManyField(Meal)
user = models.ForeignKey(User, on_delete=models.CASCADE)
def __str__(self):
return f'{self.day} - {self.user}'

我的视图集：

class DietViewSet(viewsets.ModelViewSet):
queryset = Diet.objects.all()
serializer_class = DietSerializer
pagination_class = None
def get_queryset(self):
if self.action == 'list':
self.queryset = Diet.objects.filter(user=self.request.user).order_by('day')
else:
self.queryset = Diet.objects.all().order_by('day')
return super(DietViewSet, self).get_queryset()
def get_permissions(self):
if self.action in ['list', 'retrieve']:
self.permission_classes = [permissions.AllowAny]
else:
self.permission_classes = [IsDietician]
return super(DietViewSet, self).get_permissions()

我的序列化程序：

class MealSerializer(serializers.ModelSerializer):
class Meta:
model = models.Meal
fields = '__all__'

class DietSerializer(serializers.ModelSerializer):
def to_representation(self, instance):
result = super(DietSerializer, self).to_representation(instance)
result['meals'] = MealSerializer(instance.meals, many=True).data
return result
class Meta:
model = models.Diet
fields = '__all__'

现在我想添加total_kcal，它将根据膳食数据计算。我试着通过kcal=串行器。MethodSerializerField((

和

def get_kcal(self，obj(

但我不知道如何从to_representation中的序列化对象中获取数据。

示例响应：

[
{
"id":1,
"day":1,
"user":1,
"meals":[
{
"id":4,
"name":"Rise",
"description":"",
"kcal":150.0,
"protein":3.0,
"fat":0.0,
"carbs":28.0
},
{
"id":5,
"name":"Chocoloate",
"description":"",
"kcal":200.0,
"protein":0.0,
"fat":0.0,
"carbs":100.0
}
]
}
]

Answer 1

您可以在此处使用Python的列表理解作为

class DietSerializer(serializers.ModelSerializer):
def to_representation(self, instance):
result = super(DietSerializer, self).to_representation(instance)
result['meals'] = MealSerializer(instance.meals, many=True).data
# You can use the list comprehension here as
result["kal_sum"] = sum([meal["kcal"] for meal in result['meals']])
return result
class Meta:
model = models.Diet
fields = '__all__'

Answer 2

谢谢Arakkal Abu，但我找到了其他方法；(

我添加到我的模型中：

@property
def total_kcal(self):
qs = self.meals.through.objects.all().aggregate(total_kcal=models.Sum('meal__kcal'))
return qs['total_kcal']

并将DietSerizer中的字段更改为：

fields = ['day', 'type', 'meals', 'user', 'total_kcal']