python - Django 序列化器 : why does self. fields.pop ('field_name' )工作吗？

Question

引用以下链接作为示例(其他地方也存在大量其他示例): http://www.django-rest-framework.org/api-guide/serializers/#dynamically-modifying-fields

据了解，Django 序列化器字段通常使用元组定义，该元组是不可变的:

class UserSerializer(DynamicFieldsModelSerializer):
    class Meta:
        model = User
        fields = ('id', 'username', 'email')

但是，动态更改序列化器字段的可接受方法涉及使用 pop (self.fields.pop(field_name))

class DynamicFieldsModelSerializer(serializers.ModelSerializer):

    def __init__(self, *args, **kwargs):
        # Don't pass the 'fields' arg up to the superclass
        fields = kwargs.pop('fields', None)

        # Instantiate the superclass normally
        super(DynamicFieldsModelSerializer, self).__init__(*args, **kwargs)

        if fields is not None:
            # Drop any fields that are not specified in the `fields` argument.
            allowed = set(fields)
            existing = set(self.fields)
            for field_name in existing - allowed:
                self.fields.pop(field_name)

字段如何定义？ Django 序列化程序中有预处理步骤吗？

Answer 1

看:

https://github.com/encode/django-rest-framework/blob/3fcc076d9124fc202be1a4379b6b753209c7afbe/rest_framework/serializers.py#L354

def fields(self):
    """
    A dictionary of {field_name: field_instance}.
    """
    # `fields` is evaluated lazily. We do this to ensure that we don't
    # have issues importing modules that use ModelSerializers as fields,
    # even if Django's app-loading stage has not yet run.
    if not hasattr(self, '_fields'):
        self._fields = BindingDict(self)
        for key, value in self.get_fields().items():
            self._fields[key] = value
    return self._fields

How do fields get defined?

现在应该很清楚了。

Is there a pre-processing step in Django serializers?

是的。 这个“步骤”叫做metaclass

而Serializer、Model、Forms都是元类。