在 Django REST Framework (DRF) 中正确使用 "callable default function"

Question

问题：

如何访问序列化器实例或任何相关参数 在 DRF 字段的 默认可调用函数 中？

场景：

我有一个序列化器配置如下，

<b>def bar_value_callable_function(serializer_instance):
    if serializer_instance.context['request'].method == 'GET':
        return 'return value One'
    return 'return value Two'</b></p>

<p>class FooSerializer(serializers.Serializer):
    bar = serializers.CharField(<b>source='foo.bar', default=bar_value_callable_function</b>)</pre>
当我尝试将数据序列化为 

serializer = FooSerializer(foo_instance, context={'request': request})
print(serializer.data)


我收到错误消息，

TypeError: bar_value_callable_function() missing 1 required positional argument: 'serializer_instance'

Answer 1

更新
对于DRF>=3.12，使用默认class

这个王

class DefaultBarValue:
    requires_context = True

    def __call__(self, serializer_instance):
        if serializer_instance.context['request'].method == 'GET':
            return 'return value One'
        return 'return value Two'

将class实例而不是函数传递给default 参数

<b># default callable class
class DefaultBarValue:
    """
    "Method `set_context` on defaults is deprecated and will
    no longer be called starting with 3.12. Instead set
    `requires_context = True` on the class, and accept the
    context as an additional argument.
    """
    requires_context = True  # for DRF>=3.12
    serializer_instance = None # not required for DRF>=3.12

    def set_context(self, serializer_instance): # not required for DRF>=3.12
        self.serializer_instance = serializer_instance

    def __call__(self, serializer_instance=None):
        if serializer_instance is None:  # will be None for older versions of DRF
            if self.serializer_instance.context['request'].method == 'GET':
                return 'return value One'
            return 'return value Two'
        else:  # for DRF>=3.12
            if serializer_instance.context['request'].method == 'GET':
                return 'return value One'
            return 'return value Two'</b>


# serializer
class FooSerializer(serializers.Serializer):
    bar = serializers.CharField(source='foo.bar', <b>default=DefaultBarValue()</b>)

在 Django REST Framework (DRF) 中正确使用 "callable default function"

Proper usage of "callable default function" in Django REST Framework (DRF)

python

django

django-serializer

django-rest-framework

问题：

场景：