Django实现按Order和Category分组并在Serializer中格式化返回结果

问题背景 #

现有Django模型ModelAnswer和AnswerLog，当前接口返回单个Answer对象的列表，需将相同order和category的条目合并，把answer字段改为数组形式。

实现步骤 #

1. 优化查询集，减少数据库查询 #

修改ListAnswerLogView的查询集，用select_related预加载所有关联数据，避免多次查询数据库：

class ListAnswerLogView(generics.ListAPIView):
    def get_queryset(self):
        return AnswerLog.objects.select_related(
            'answer', 
            'answer__questions', 
            'answer__questions__category'
        ).order_by('order', 'answer__questions__category__name')

2. 新增分组序列化器 #

创建专门处理分组结构的序列化器，其中answer字段设置为多实例序列化模式：

class GroupedAnswerLogSerializer(serializers.Serializer):
    order = serializers.PositiveIntegerField()
    category = serializers.CharField()
    answer = ListAnswerSerializer(many=True)

3. 重写视图list方法实现分组逻辑 #

用itertools.groupby对查询结果按order和category分组，再将分组后的数据传入新序列化器：

import itertools

class ListAnswerLogView(generics.ListAPIView):
    serializer_class = serializers.GroupedAnswerLogSerializer

    def get_queryset(self):
        return AnswerLog.objects.select_related(
            'answer', 
            'answer__questions', 
            'answer__questions__category'
        ).order_by('order', 'answer__questions__category__name')

    def list(self, request, *args, **kwargs):
        queryset = self.filter_queryset(self.get_queryset())
        
        # 定义分组依据：order和category的组合
        def group_key(item):
            return (item.order, item.answer.questions.category.name)
        
        grouped_data = []
        # 遍历分组结果，组装成目标格式
        for (order, category), group in itertools.groupby(queryset, key=group_key):
            grouped_data.append({
                'order': order,
                'category': category,
                'answer': [item.answer for item in group]
            })
        
        serializer = self.get_serializer(grouped_data, many=True)
        return Response(serializer.data)

最终返回效果 #

接口将返回合并后的结构，符合预期格式：

[{
    "answer": [{
        "id": 42,
        "user": 1,
        "questions": "what did you do today",
        "subcategory": "Circumstance",
        "is_intentional": "False",
        "answer": "I played well",
        "created_at": "2022-09-05T21:00:57.604051"
    }, {
        "id": 43,
        "user": 1,
        "questions": "what was your achievment?",
        "subcategory": "Result",
        "is_intentional": "False",
        "answer": "a broked my leg",
        "created_at": "2022-09-05T21:00:57.626193"
    }],
    "order": 1,
    "category": "sports"
}]

内容的提问来源于stack exchange，提问作者lord stock