如何在序列化程序中使用 count() 和 sum()？答案

【问题标题】：How to use count() and sum() in serializer?如何在序列化程序中使用 count() 和 sum()？
【发布时间】：2023-02-06 16:31:26
【问题描述】：

我想计算 sum_of_rating/number_of_rating 的平均评分。

class SearchWorkingProfessionals(APIView):
    def post(self,request,format=None):
        tags = request.data.get('tag_arr')
        city_name = request.data.get('city_name')
        tags_list = tags.split(',')
        ws = WorkSamplesModel.objects.filter(business_account__serviceareasmodel__city_name=city_name,
        business_account__professiontagsmodel__tag_name__in=tags_list,
        is_business_card_image=True).distinct()
        serializer = SearchWorkingProgessionalsSerializer(ws,many=True)
        resp = {'resp':serializer.data}
        return Response(resp)

class FeedbackModel(models.Model):
    feedback_text = models.CharField(max_length=20)
    rating = models.IntegerField()
    business_account = models.ForeignKey(BusinessAccountModel,on_delete=models.CASCADE)
    
    class Meta:
        db_table = 'feedback'

这是我当前的序列化程序

class SearchWorkingProgessionalsSerializer(serializers.Serializer):
    business_account_id = serializers.IntegerField()
    first_name = serializers.CharField(source='business_account.user.first_name')
    last_name = serializers.CharField(source='business_account.user.last_name')
    profile_pic = serializers.ImageField(source='business_account.user.profile_pic')
    business_title = serializers.CharField(source='business_account.business_title')
    business_description = serializers.CharField(source='business_account.business_description')
    status = serializers.CharField(source='business_account.status')
    note = serializers.CharField(source='business_account.note')
    work_sample_image = serializers.ImageField()
    work_sample_description = serializers.CharField(max_length=1000)

class WorkSamplesModel(models.Model):
    work_sample_image = models.ImageField(blank=True,null=True,upload_to="work_samples")
    work_sample_description = models.CharField(max_length=1000)
    is_business_card_image = models.BooleanField(default=False)
    business_account = models.ForeignKey(BusinessAccountModel,on_delete=models.CASCADE)

如何使用此序列化程序计算平均评分？

【问题讨论】：

标签： django django-models django-rest-framework django-views django-serializer

【解决方案1】：

在这种情况下，您唯一的选择是使用SerializerMethodField。这样的事情应该有效（如果我理解你的要求）：

from django.db.models import Avg

class SearchWorkingProgessionalsSerializer(serializers.Serializer):
    count_feedbacks = serializer.SerializerMethodField()
    average_rating = serializer.SerializerMethodField()

    # Returns the number of ratings
    def get_count_feedbacks(self, instance):
        return instance.business_account.feedbackmodel_set.count()  

    # Returns the average rating
    def get_average_rating(self, instance)
        return instance.business_account.feedbackmodel_set.aggregate(average_rating=Avg('rating'))['average_rating']

【讨论】：

类型错误：QuerySet.aggregate() 收到非表达式：评级。错误显示为 get_average_rating() get_count_feedbacks() 工作正常..

【解决方案2】：

您始终可以编写 serializers.SerializerMethodField() 以在序列化程序中返回动态计算的字段。

在您的具体情况下，您还应该发布 WorkSamplesModel 以便更清楚。

【讨论】：

【解决方案3】：

以下代码对我有用..！

from django.db.models import Avg
...


class SearchWorkingProfessionalsSerializer(serializers.Serializer):
    business_account_id = serializers.IntegerField()
    first_name = serializers.CharField(source='business_account.user.first_name')
    last_name = serializers.CharField(source='business_account.user.last_name')
    profile_pic = serializers.ImageField(source='business_account.user.profile_pic')
    business_title = serializers.CharField(source='business_account.business_title')
    business_description = serializers.CharField(source='business_account.business_description')
    status = serializers.CharField(source='business_account.status')
    note = serializers.CharField(source='business_account.note')
    work_sample_image = serializers.ImageField()
    work_sample_description = serializers.CharField(max_length=1000)
    feedback_count = serializers.SerializerMethodField('get_feedback_count')
    average_rating = serializers.SerializerMethodField()

    def get_feedback_count(self, instance):
        return instance.business_account.feedbackmodel_set.count()

    def get_average_rating(self, instance):
        return instance.business_account.feedbackmodel_set.aggregate(average_rating=Avg('rating'))['average_rating']

【讨论】：