python - Django Rest Framework - TaggableManager 字段的反序列化

Question

我用了django-taggit向我的模型添加标签。 Django版本:2.2.10，Python版本:3.8.1

现在我正在尝试将标签与 django Rest-framework 集成，例如创建/更新/删除带/不带标签的模型实例。

我的问题:我无法(通过rest api)使用标签创建模型的新实例。我可以毫无问题地获取模型实例。

我的模型.py:

from taggit.managers import TaggableManager

class Task(models.Model):
    name = models.CharField(max_length=100, blank=False)
    ...
    tags = TaggableManager(blank=True)

    def get_tags(self):
        """ names() is a django-taggit method, returning a ValuesListQuerySet 
        (basically just an iterable) containing the name of each tag as a string
        """
        return self.tags.names()

    def __str__(self):
        return self.title

我的序列化器.py:

class TagsField(serializers.Field):
    """ custom field to serialize/deserialize TaggableManager instances.
    """
    def to_representation(self, value):
        """ in drf this method is called to convert a custom datatype into a primitive,
        serializable datatype.

        In this context, value is a plain django queryset containing a list of strings.
        This queryset is obtained thanks to get_tags() method on the Task model.

        Drf is able to serialize a queryset, hence we simply return it without doing nothing.
        """
        return value

    def to_internal_value(self, data):
        """ this method is called to restore a primitive datatype into its internal
        python representation.

        This method should raise a serializers.ValidationError if the data is invalid.
        """
        return data

class TaskSerializer(serializers.ModelSerializer):

    # tags field in Task model is implemented via TaggableManager class from django-taggit.
    # By default, drf is not able to serialize TaggableManager to json.
    # get_tags() is a method of the Task model class, which returns a Queryset containing
    # the list of tags as strings. This Queryset can be serialized without issues.
    tags = TagsField(source="get_tags")

    class Meta:
        model = Task
        fields = [
                "name",
                ...,
                "tags",
            ]

每当我尝试通过 POST api 创建任务模型的新实例时，都会收到以下错误:

TypeError at /taskdrop/v1/task/
Got a `TypeError` when calling `Task.objects.create()`. This may be because you have a writable field on the serializer class that is not a valid argument to `Task.objects.create()`. You may need to make the field read-only, or override the TaskSerializer.create() method to handle this correctly.
Original exception was:
 Traceback (most recent call last):
  File "/home/daniele/prj/ea/TaskDrop/venv/lib/python3.8/site-packages/rest_framework/serializers.py", line 948, in create
    instance = ModelClass._default_manager.create(**validated_data)
  File "/home/daniele/prj/ea/TaskDrop/venv/lib/python3.8/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/daniele/prj/ea/TaskDrop/venv/lib/python3.8/site-packages/django/db/models/query.py", line 420, in create
    obj = self.model(**kwargs)
  File "/home/daniele/prj/ea/TaskDrop/venv/lib/python3.8/site-packages/django/db/models/base.py", line 501, in __init__
    raise TypeError("%s() got an unexpected keyword argument '%s'" % (cls.__name__, kwarg))
TypeError: Task() got an unexpected keyword argument 'get_tags'

我现在有点卡住了......该字段绝对不是只读的，并且关于覆盖 TaskSerializer.create() 方法，我不知 Prop 体该怎么做。

另外，我对 TagsField(serializers.Field) 与 .create() 方法重写有点困惑。根据我的理解，如果我创建自定义序列化器字段，则不需要额外重写 .create()。

最后，我尝试使用django-taggit-serializer不成功:模型已创建，但传递的标签丢失。

我该如何解决这个问题？谢谢。

Answer 1

好的，我成功了。

将解决方案留给其他人:

我得到的原因 TypeError: Task() got an Unexpected keywords argument 'get_tags' 是因为 drf 试图使用 to_internal_value() 的返回值来填充 'get_tags' 字段我的模型。

现在，“get_tags”只是我的模型任务类的方法名称，而不是真正的字段，因此会出现错误。当我在序列化器中使用 tags = TagsField(source="get_tags") 时，Drf 了解到“get_tags”作为字段名称。

我通过重写序列化器的 create() 方法解决了这个问题，方法如下:

class TaskSerializer(serializers.ModelSerializer):

    # tags field in Task model is implemented via TaggableManager class from django-taggit.
    # By default, drf is not able to serialize TaggableManager to json.
    # get_tags() is a method of the Task model class, which returns a Queryset containing
    # the list of tags as strings. This Queryset can be serialized without issues.
    tags = TagsField(source="get_tags")
    # variables = VariableSerializer()

    def create(self, validated_data):
        # using "source=get_tags" drf "thinks" get_tags is a real field name, so the
        # return value of to_internal_value() is used a the value of a key called "get_tags" inside validated_data dict. We need to remove it and handle the tags manually.
        tags = validated_data.pop("get_tags")
        task = Task.objects.create(**validated_data)
        task.tags.add(*tags)

        return task

    class Meta:
        model = Task
        # we exclude all those fields we simply receive from Socialminer
        # whenever we get a task or its status
        fields = [
                "name",
                 ...
                "tags",
            ]