DRF Serializer 的many參數是幹嗎的

Django rest framework

何時須要用many參數呢？

• 當構造序列化的時候，傳遞的參數的QuerySet實例，就須要用many=True參數，即使QuerySet長度爲0或者長度爲1
• 當構造序列化的時候，傳遞的參數的某個模型實例（內置的User實例，或者自定義的模型實例），就須要用many=false參數

源碼解析

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)

當使用以下的語句進行序列化操做的時候。
serializer = TweetSerializer(queryset, many=True)
queryset會被賦值給BaseSerializer對應的構造方法def __init__(self, instance=None, data=empty, **kwargs):中的instance參數。
當instance參數接受的是QuerySet實例，就須要加many=True，若是instance接受的某個模型實例，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='標題')
    content = models.TextField(verbose_name='正文')

    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):
        # 這裏是你執行 print(tweet instance) 的時候會顯示的內容
        return '{} {}: {}'.format(self.created_at, self.user, self.content)