Django Rest Framework 3.7.7 不处理 Null/None ForeignKey 值

Question

当我的 ForeignKey 包含空值时，Django Rest Framework 出现错误。

unit = models.ForeignKey(
        SubLocation,
        on_delete=models.CASCADE,
        related_name='unit',
        blank=True,
        null=True,
)

class AssetSerializer(serializers.ModelSerializer):

    unit = serializers.PrimaryKeyRelatedField(
        source='unit.name',
        allow_null=True,
        default=None,
        queryset=SubLocation.objects.all(),
    )

    class Meta:
        model = Asset
        fields = ('pk', 'unit',
        )

访问这个序列化器的数据属性，当unit外键字段为None时

>> ass = Asset.objects.first()
>> AssetSerializer(ass).data

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "C:\Python36\lib\site-packages\rest_framework\serializers.py", line 537, in data
    ret = super(Serializer, self).data
  File "C:\Python36\lib\site-packages\rest_framework\serializers.py", line 262, in data
    self._data = self.to_representation(self.instance)
  File "C:\Python36\lib\site-packages\rest_framework\serializers.py", line 491, in to_representation
    attribute = field.get_attribute(instance)
  File "C:\Python36\lib\site-packages\rest_framework\relations.py", line 177, in get_attribute
    return get_attribute(instance, self.source_attrs)
  File "C:\Python36\lib\site-packages\rest_framework\fields.py", line 100, in get_attribute
    instance = getattr(instance, attr)
AttributeError: 'NoneType' object has no attribute 'unit'

如您所见，设置 allow_null 仍然不起作用，并且 drf 似乎在提示 NoneType 对象。

我怎样才能修复这个错误，以便我可以在 drf 中使用空值？

Answer 1

我刚刚升级自己并遇到了这个。快速谷歌一下，在文档中找到了这个:

When serializing fields with dotted notation, it may be necessary to provide a default value if any object is not present or is empty during attribute traversal.