Question

我将如何在Django REST框架中更新多对多关系？

这是我的模特。

class SchoolTeacher(AbstractBase):
    school = models.ForeignKey(School, on_delete=models.CASCADE, 
         related_name='teachers')
    user = models.ForeignKey(User, on_delete=models.CASCADE, 
         related_name='teacher_at',)
    subjects = models.ManyToManyField(SchoolSubject, 
        related_name='teachers')

这是我的序列化器：

class SchoolTeacherSerializer(serializers.ModelSerializer):
   ....
   def create(self, validated_data):
    school_class = validated_data.get('school_class', None)
    stream = validated_data.get('stream', None)

    school_teacher_model_fields = [
        f.name for f in SchoolTeacher._meta.get_fields()]
    valid_teacher_data = {
        key: validated_data[key]
        for key in school_teacher_model_fields
        if key in validated_data.keys()
    }
    subjects = valid_teacher_data.pop('subjects')
    teacher = SchoolTeacher.objects.create(**valid_teacher_data)

    for subject in subjects:
        teacher.subjects.add(subject)

    self.add_class_teacher(stream, school_class, teacher)

    return teacher

def update(self, instance, validated_data):
    subjects = validated_data.pop('subjects')
    school_class = validated_data.get('school_class', None)
    stream = validated_data.get('stream', None)
    teacher = instance

    for (key, value) in validated_data.items():
        setattr(teacher, key, value)

    for subject in subjects:
        teacher.subjects.add(subject)

    teacher.save()

    return teacher

如何实现更新subjects？目前，我只能添加而不可以删除现有主题。

Answer 1

在我们谈论多对多时，必须先将两个对象持久化，然后才能将它们彼此分配。

一旦有了，就可以简单地将一个添加到另一个的about集合中，如下所示（来源：https://docs.djangoproject.com/en/2.1/topics/db/examples/many_to_many/）：

a1 = Article(headline='Django lets you build Web apps easily')
a1.save()
p1 = Publication(title='The Python Journal')
p1.save()
a1.publications.add(p1)

或者，一步：

new_publication = a1.publications.create(title='Highlights for Children')

我还没有找到如何表达“包含”的方法，但是下一步是删除不在新列表中的主题，并添加新列表而不是旧列表中的主题。排序列表或更好的散列可能更有效。但是我的python还不够好。

Answer 2

这是一种解决方法。但我希望有人能发布更好的答案。这里的想法是先删除所有主题，然后再添加它们。但是，由于我们当然不能做teacher.subjects.all().delete()，所以我们可以做

    for existing_subject in teacher.subjects.all():
        teacher.subjects.remove(existing_subject)

    for subject in subjects:
        teacher.subjects.add(subject)

如何更新多对多Django REST？

2 个答案: