带有Django REST框架的AttributeError和多人关系

Question

试图访问我的json页面，我得到了这个错误！

AttributeError at /project/api/1.json
Got AttributeError when attempting to get a value for field `title` on serializer `TaskSerializer`.
The serializer field might be named incorrectly and not match any attribute or key on the `RelatedManager` instance.
Original exception text was: 'RelatedManager' object has no attribute 'title'.

我和我的模特有很多关系：

class Project(models.Model):
    owner = models.ForeignKey('auth.User')
    title = models.CharField(max_length=100)
    slug = models.SlugField(unique=True)
    created_date = models.DateTimeField(auto_now_add=True, auto_now=False)
    updated_date = models.DateTimeField(auto_now_add=False, auto_now=True)

    def __str__(self):
        return self.title

    def save(self, **kwargs):
        super(Project, self, **kwargs).save()
        self.slug = slugify(self.title)
        super(Project, self, **kwargs).save()

    def create(self):
        pass


class Task(models.Model):
    title = models.CharField(max_length=100)
    description = models.TextField(blank=True)
    completed = models.BooleanField(default=False)
    project = models.ForeignKey('Project', related_name="tasks")
    dependency = models.ManyToManyField('self', through='Dependency', null=True, 
        blank=True, through_fields=('task', 'sub_task'), symmetrical=False)

    def sub_tasks(self, **kwargs):
        qs = self.dependency.filter(**kwargs)
        for sub_task in qs:
            qs = qs | sub_task.sub_tasks(**kwargs)
        return qs

    def __str__(self):
        return self.title

class Dependency(models.Model):
    task = models.ForeignKey(Task, related_name="dependency_task")
    sub_task = models.ForeignKey(Task, related_name="dependency_sub_task")

这些序列化程序：

class TaskSerializer(serializers.ModelSerializer):
    class Meta:
        model = Task
        fields = ('id', 'title', 'project', 'completed',)


class ProjectSerializer(serializers.ModelSerializer):
    tasks = TaskSerializer()
    class Meta:
        model = Project
        fields = ('id', 'title', 'tasks',)

我怎样才能避开这件事？RelatedManager告诉我，我的M2M链接有问题，但为什么/如何解决？我看不到任何关于属性错误的here。

这个问题似乎是相关的，但是设置many=False没有任何作用。

AttributeError with Django REST Framework and MongoEngine

Answer 1

在这个问题上，他们设置了many=False。你的确有多对多，所以设置many=True就这么简单。

事实上，如果你仔细观察，这就是示例向你展示的方法：

class TrackListingField(serializers.RelatedField):
    def to_representation(self, value):
        duration = time.strftime('%M:%S', time.gmtime(value.duration))
        return 'Track %d: %s (%s)' % (value.order, value.name, duration)

class AlbumSerializer(serializers.ModelSerializer):
    tracks = TrackListingField(many=True)

    class Meta:
        model = Album
        fields = ('album_name', 'artist', 'tracks')

查看tracks listing字段如何具有many=True属性？做那件事。

Answer 2

当我错过指定指向Album模型的ForeignKeyField定义的related_name属性时，我也遇到了类似的问题。