Django rest framework

什么时候须要用many参数呢？

  • 当结构序列化的时候，传递的参数的QuerySet实例，就须要用many=True参数，即使QuerySet长度为0或者长度为1
  • 当结构序列化的时候，传递的参数的某个模型实例（内置的User实例，或者自定义的模型实例），就须要用many=false参数

源码解析

class BaseSerializer(Field):    def __init__(self, instance=None, data=empty, **kwargs):        self.instance = instance        if data is not empty:            self.initial_data = data        self.partial = kwargs.pop('partial', False)        self._context = kwargs.pop('context', {})        kwargs.pop('many', None)        super().__init__(**kwargs)            def __new__(cls, *args, **kwargs):        if kwargs.pop('many', False):            return cls.many_init(*args, **kwargs)        return super().__new__(cls, *args, **kwargs)    @classmethod    def many_init(cls, *args, **kwargs):        allow_empty = kwargs.pop('allow_empty', None)        child_serializer = cls(*args, **kwargs)        list_kwargs = {            'child': child_serializer,        }        if allow_empty is not None:            list_kwargs['allow_empty'] = allow_empty        list_kwargs.update({            key: value for key, value in kwargs.items()            if key in LIST_SERIALIZER_KWARGS        })        meta = getattr(cls, 'Meta', None)        list_serializer_class = getattr(meta, 'list_serializer_class', ListSerializer)        return list_serializer_class(*args, **list_kwargs)

当应用如下的语句进行序列化操作的时候。
serializer = TweetSerializer(queryset, many=True)
queryset会被赋值给BaseSerializer对应的构造方法def __init__(self, instance=None, data=empty, **kwargs):中的instance参数。
当instance参数承受的是QuerySet实例，就须要加many=True，如果instance承受的某个模型实例，例如TweetModel

class TweetAPIView(mixins.ListModelMixin,                   mixins.CreateModelMixin,                   GenericAPIView                   ):    queryset = TweetModel.objects.all()    serializer_class = TweetCreateSerializer    def get(self, request: Request):        return self.list(request)    def list(self, request, *args, **kwargs):        queryset = self.filter_queryset(self.get_queryset())        serializer = TweetSerializer(queryset, many=True)        return Response(serializer.data)    def post(self, request: Request):        return self.create(request)
class TweetModel(models.Model):    user = models.ForeignKey(User, on_delete=models.SET_NULL, null=True)    title = models.CharField(max_length=32, verbose_name='题目')    content = models.TextField(verbose_name='注释')    photos = models.ManyToManyField(Photo, blank=True)    likes_count = models.BigIntegerField(default=0, null=True)    comments_count = models.BigIntegerField(default=0, null=True)    read_count = models.BigIntegerField(default=0, null=True)    created_at = models.DateTimeField(auto_now_add=True)    updated_at = models.DateTimeField(auto_now=True)    class Meta:        index_together = (('user', 'created_at'),)    def __str__(self):        # 这里是你执行 print(tweet instance) 的时候会显示的内容        return '{} {}: {}'.format(self.created_at, self.user, self.content)