异常值：类型对象“纪律”没有属性“描述”答案

【问题标题】：Exception Value: type object 'Discipline' has no attribute 'description'异常值：类型对象“纪律”没有属性“描述”
【发布时间】：2015-12-09 20:58:03
【问题描述】：

所以，我正在使用 Django Rest Framework 构建我的第一个 Django 项目，并且上面有这 3 个模型：

class Student(models.Model):
    user = models.OneToOneField(User, unique=True)
    ra = models.IntegerField()

class Discipline (models.Model):
    description = models.CharField(max_length=150)
    professor = models.ForeignKey(Professor, related_name='disciplines')
    learners = models.ManyToManyField('students.Student', through='enrollments.enrollment', related_name='disciplines')

class Enrollment (models.Model):
    discipline = models.ForeignKey('disciplines.Discipline')
    student = models.ForeignKey(Student)
    enroll_date = models.DateField(auto_now_add=True)

对于这些模型，我有这些序列化程序：

class StudentSerializer (serializers.ModelSerializer):
     ra = serializers.IntegerField(source=Student.ra)
     disciplines = EnrolledDisciplinesSerializer(source="enrollment_set", many=True)
     activities = RealizedActivitiesSerializer(source='activities_set', many=True)

     class Meta:
         model = User
         fields = ('id','username', 'email', 'password', 'ra', 'disciplines','activities')

class DisciplineSerializer (serializers.ModelSerializer):
     professor = serializers.StringRelatedField()
     learners = LearnersSerializer(source="enrollment_set", many=True)

     class Meta:
         model = Discipline
         fields = ('id', 'description', 'professor', 'learners')

class EnrolledDisciplinesSerializer(serializers.ModelSerializer):
     id = serializers.ReadOnlyField(source=Discipline.pk)
     description = serializers.ReadOnlyField(source=Discipline.description)

    class Meta:
        model = Enrollment
        fields = ('id', 'description', 'enroll_date')


class LearnersSerializer(serializers.ModelSerializer):
    id = serializers.ReadOnlyField(source=Student.pk)
    ra = serializers.ReadOnlyField(source=Student.ra)

    class Meta:
        model = Enrollment
        fields = ('id', 'ra', 'enroll_date')

在我的学生应用程序的 views.py 中，我有以下代码：

class StudentList (generics.ListCreateAPIView):
    model = Student
    serializer_class = StudentSerializer
    permission_classes = [
        permissions.IsAuthenticatedOrReadOnly,
    ]


class StudentDetail (generics.RetrieveAPIView):
    model = Student
    serializer_class = StudentSerializer


class StudentDisciplineList (generics.ListAPIView):
    model = Enrollment
    serializer_class = EnrolledDisciplinesSerializer

    def get_queryset(self):
        queryset = super(StudentDisciplineList, self).get_queryset()
        return queryset.filter(student__pk=self.kwargs.get('pk'))


class StudentActivitiesList (generics.ListAPIView):
    model = Activity
    serializer_class = ActivitiesSerializer

    def get_queryset(self):
        queryset = super(StudentActivitiesList, self).get_queryset()
        return queryset.filter(student__pk=self.kwargs.get('pk'))

创建视图后，我将以下内容添加到学生应用程序中的 urls.py 文件中：

url_patterns = [
    '',
    url(r'^/(?P<pk>\d+)/disciplines$', StudentDisciplineList.as_view(), name='studentdiscipline-list'),
    url(r'^/(?P<pk>\d+)/activities$', StudentActivitiesList.as_view(), name='studentactivities-list'),
    url(r'^/(?P<pk>\d+)$', StudentDetail.as_view(), name='student-detail'),
    url(r'^$', StudentList.as_view(), name='student-list'),
]

然后我将它添加到我的主 urls.py 文件中：

import students.urls

urlpatterns = [
    url(r'^admin/', include(admin.site.urls)),
    url(r'^students/', include(students.urls)),
]

完成此操作后，我去了http://127.0.0.1:8000/students并得到以下信息：

File "C:\Users\Douglas\tg_project\enrollments\serializers.py" in EnrolledDisciplinesSerializer


9.     description = serializers.ReadOnlyField(source=Discipline.description)

Exception Type: AttributeError at /admin
Exception Value: type object 'Discipline' has no attribute 'description'

我已经在 Google 和 StackOverflow 上搜索过这方面的内容，但找不到可以帮助我的东西。我还查看了整个代码，看看我是否没有输入任何拼写错误，但似乎一切正常。

非常感谢为解决此问题提供的任何帮助。

【问题讨论】：

为什么discipline = models.ForeignKey('disciplines.Discipline') 在Enrollment 模型中，而不仅仅是discipline = models.ForeignKey(Discipline)？
@Pynchia 每当我尝试这样做时，我都会在 f.rel.through._meta.local_fields 中收到以下 m2m 错误：AttributeError: 'str' object has no attribute '_meta'

标签： python django django-rest-framework django-1.8

【解决方案1】：

source 应该是一个字符串，其中包含要从Enrollment 实例获取的属性。所以在你的EnrolledDisciplinesSerializer 中，对于description，你需要'discipline.description'。 discipline（小写）是用于访问该注册的学科的属性名称，description 是用于获取该学科实例的描述的名称。其他领域也一样。

Django 使用元类来构建模型。这种工作方式，您在模型中定义的字段最终不会成为类的属性。这意味着Discipline 类将没有属性Discipline.description。只有Discipline 的实例具有description 属性。

【讨论】：