我已经阅读了一堆类似SO的声音问题，但不知怎的，它们都没有帮助我解决我的具体案例。我添加了一个ManyToManyField代表“喜欢”到我的Photo模型：
class Photo(TimestampModerated):
owner = models.ForeignKey('auth.User', related_name='photos', on_delete=models.CASCADE)
uuid = models.UUIDField(default=uuid4, editable=False)
slug = models.SlugField(max_length=80, editable=False)
title = models.CharField(max_length=80, blank=False, null=False)
description = models.TextField(verbose_name='description of entity', blank=True, null=True)
photo = models.ImageField(upload_to=user_directory_path, height_field="height", width_field="width", blank=True)
height = models.IntegerField(blank=True)
width = models.IntegerField(blank=True)
tags = TaggableManager(blank=True)
hash = models.CharField(max_length=64, unique=True, null=True)
size = models.BigIntegerField('size of file in bytes', blank=True, null=True)
likes = models.ManyToManyField('auth.User', blank=True, null=True)
class Meta:
verbose_name_plural = "photos"
def __str__(self):
return self.title
def delete(self, using=None, keep_parents=False):
default_storage.delete("{}".format(self.photo))
super().delete()
def save(self, *args, **kwargs):
self.slug = slugify(self.title)
super(Photo, self).save(*args, **kwargs)
以下是视图（至少是创建的重要部分）：
class PhotoViewSet(viewsets.ModelViewSet):
queryset = Photo.objects.all()
serializer_class = PhotoSerializer
authentication_classes = (TokenAuthentication,)
permission_classes = (IsOwnerOrReadOnly, permissions.AllowAny,)
parser_classes = (MultiPartParser, FormParser)
def perform_create(self, serializer):
serializer.save(owner=self.request.user, likes=[])
这是序列化器：
class PhotoSerializer(serializers.ModelSerializer, TaggitSerializer):
owner = serializers.CharField(source='owner.username', read_only=True)
tags = TagListSerializerField()
photo = Base64ImageField(
max_length=None, use_url=True,
)
class Meta:
model = Photo
fields = ('photo', 'height', 'width', 'owner', 'slug', 'uuid', 'title', 'id', 'created', 'updated',
'moderation_code', 'tags', 'hash', 'description', 'size', 'likes')
def create(self, validated_data):
photo = Photo.objects.create(owner=validated_data.pop('owner'),
**validated_data)
p = Photo.objects.get(uuid=photo.uuid)
[p.tags.add(tag) for tag in validated_data['tags']]
return photo
要清楚，唯一添加的是模型中的likes字段。此外，我应该注意到，我能够在迁移之前将新的喜欢发布到已经存在于数据库中的照片。我只是在创建新实例时遇到问题。有什么想法吗？
以下是完整的错误追溯：
Internal Server Error: /api/photos/
Traceback (most recent call last):
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/django/core/handlers/exception.py", line 41, in inner
response = get_response(request)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/django/core/handlers/base.py", line 187, in _get_response
response = self.process_exception_by_middleware(e, request)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/django/core/handlers/base.py", line 185, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/django/views/decorators/csrf.py", line 58, in wrapped_view
return view_func(*args, **kwargs)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/rest_framework/viewsets.py", line 86, in view
return self.dispatch(request, *args, **kwargs)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/rest_framework/views.py", line 489, in dispatch
response = self.handle_exception(exc)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/rest_framework/views.py", line 449, in handle_exception
self.raise_uncaught_exception(exc)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/rest_framework/views.py", line 486, in dispatch
response = handler(request, *args, **kwargs)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/rest_framework/mixins.py", line 21, in create
self.perform_create(serializer)
File "/Users/xxxxxx/_/photos/views.py", line 24, in perform_create
serializer.save(owner=self.request.user, likes=[])
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/rest_framework/serializers.py", line 215, in save
self.instance = self.create(validated_data)
File "/Users/xxxxxx/_/photos/serializers.py", line 88, in create
**validated_data)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/django/db/models/manager.py", line 85, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/django/db/models/query.py", line 392, in create
obj = self.model(**kwargs)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/django/db/models/base.py", line 566, in __init__
_setattr(self, prop, kwargs[prop])
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py", line 536, in __set__
manager = self.__get__(instance)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py", line 513, in __get__
return self.related_manager_cls(instance)
File "/Users/xxxxxx/_/.virtualenv/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py", line 830, in __init__
(instance, self.pk_field_names[self.source_field_name]))
ValueError: "<Photo: photo-260561.jpeg>" needs to have a value for field "id" before this many-to-many relationship can be used.
答案 0 :(得分：0)
好吧，我用一个看似非常简单的代码解决了这个问题：
def create(self, validated_data):
validated_data.pop('likes') ## adding this line solved the issue
photo = Photo.objects.create(owner=validated_data.pop('owner'),
**validated_data)
p = Photo.objects.get(uuid=photo.uuid)
[p.tags.add(tag) for tag in validated_data['tags']]
return photo
如果有人能解释为什么会这样，我有兴趣知道。我应该指出，对于这个用例，照片永远不会用喜欢的方式启动。