Django - 以一对多关系选择嵌套集合平均值与分组

Posted 2023-02-24

【中文标题】Django - 以一对多关系选择嵌套集合平均值与分组

【英文标题】：Django - Select nested collection Avg with group by in one to many relationship

【发布时间】：2018-09-10 06:13:40

【问题描述】：

我有以下模型，我想要选择一个业务集合，每个业务都有一个基于 group by review_question_id 的 AVG(rate) 集合。

以下是必要的模型：

class ReviewQuestion(models.Model):
    """Represents a question to be given in a business type
    """
    business_type = models.ForeignKey(BusinessType, on_delete=models.CASCADE)
    question_text = models.CharField(max_length=100)


class Business(models.Model):
    """Values for a specific business, based on a type
    will inherit questions and reviews
    """
    business_type = models.ForeignKey(BusinessType, on_delete=models.CASCADE)
    name = models.CharField(max_length=100)


class CustomerReview(models.Model):
    """Rate value by customers on a specific quesiton
    for a specific business
    """
    business = models.ForeignKey(Business, on_delete=models.CASCADE)
    review_question = models.ForeignKey(
        ReviewQuestion, on_delete=models.CASCADE)
    review_value = models.PositiveSmallIntegerField()

我试图接近的最近的查询：

items = Business.objects.filter(business_type_id=type_id).values(
        'id', 'name', 'business_type_id', 'address', 'customerreview__review_question_id').annotate(rate=Avg('customerreview__review_value'))

它的问题是重复。它复制了整个列表，结果是扁平的，就像你用扁平 tsql 编写它时得到的一样。

理想的结果应该是这样的：

[
    
        "business_id": 1,
        "business_name": "something",
        "rating":[
            
                "Question_1":
                    "title":"ReviewQuestion__question_text",
                    "Avg":5.0
                ,
                "Question_2":
                    "title":"ReviewQuestion__question_text",
                    "Avg":5.0
                ,
                    ...
                
            
        ]
    
]

如果我是 python/django 的新手，我将不胜感激。

【参考方案1】：

如果你使用 django-rest-framework 会很容易。 您应该使用两个序列化程序。

from rest_framework import serializers

class BussnessSerializer(serializers.ModelSerializer):
     rating = QuestionWithRatingSerializer(
                  source='reviewquestion_set', 
                  many=True
     )
     business_id = serializers.IntegerField(source='id')
     business_name = serizlizers.CharField(source='name')


     class Meta:
           model = Business
           fields = ('rating', 'business_id', 'business_name')


class QuestionWithRatingSerializer(serializers.ModelSerializer):
      title = serializers.CharField(source='question_text')
      avg = serizlizers.SerializerMethodField()

      def get_avg(self, obj):

          return obj.customerreview_set.aggregave(
                     avg=Avg('review_value')['avg'])

      class Meta:
           model = ReviewQuestion
           fields = ('title', 'avg')

【讨论】：

您好，感谢您的回复，因为我说我是新来的。这应该是某种 ViewModel（例如 c# linq viewModels）还是我应该更改我的模型以匹配它？

啊，不。我关注的是来自 docs.djangoproject.com 的文档，而不是来自 rest-framework 的文档..

如果你愿意，你可以在你的 django 项目中使用 django-rest-framework(django-rest-framework.org)