创建UserInfo对象时出现“matching query does not exist”错误排查

问题代码 #

class GoogleSignIn(APIView):
    def post(self, request):
        settings = request.settings
        code = request.data['code']

        # 验证Google OAuth授权码
        try:
            google_user_info = verify_user(code)
        except Exception as e:
            print(str(e))
            return Response({'error': 'Failed to verify with Google.'})

        email = google_user_info['email']
        picture = google_user_info['picture']
        try:
            user = User.objects.get(email=email)
            user_info = UserInfo.objects.get(user=user)
        except User.DoesNotExist:
            first_name = google_user_info['given_name']
            user = User.objects.create_user(
                email = email,
                username = email,
                first_name = first_name,
                last_name = google_user_info['family_name'],
                password=None)
            user_info = UserInfo.objects.create(
                user = user,
                credits = request.settings.INITIAL_CREDITS,
                expiry = compute_credits_expiry(
                    num_days=settings.FREE_CREDITS_EXPIRY_IN_DAYS))

异常信息 #

Internal Server Error: /accounts/google-sign-in/
Traceback (most recent call last):
  File "/mnt/c/Dropbox/Parnasa/Web/wherewasit/backend/accounts/views.py", line 129, in post
    user = User.objects.get(email=email)
  File "/usr/lib/python3/dist-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/django/db/models/query.py", line 435, in get
    raise self.model.DoesNotExist(
django.contrib.auth.models.User.DoesNotExist: User matching query does not exist.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/usr/lib/python3/dist-packages/django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/lib/python3/dist-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/django/views/generic/base.py", line 70, in view
    return self.dispatch(request, *args, **kwargs)
  File "/home/meir/.local/lib/python3.10/site-packages/rest_framework/views.py", line 509, in dispatch
    response = self.handle_exception(exc)
  File "/home/meir/.local/lib/python3.10/site-packages/rest_framework/views.py", line 469, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/home/meir/.local/lib/python3.10/site-packages/rest_framework/views.py", line 480, in raise_uncaught_exception
    raise exc
  File "/home/meir/.local/lib/python3.10/site-packages/rest_framework/views.py", line 506, in dispatch
    response = handler(request, *args, **kwargs)
  File "/mnt/c/Dropbox/Parnasa/Web/wherewasit/backend/accounts/views.py", line 140, in post
    user_info = UserInfo.objects.create(
  File "/usr/lib/python3/dist-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/django/db/models/query.py", line 453, in create
    obj.save(force_insert=True, using=self.db)
  File "/usr/lib/python3/dist-packages/django/db/models/base.py", line 739, in save
    self.save_base(using=using, force_insert=force_insert,
  File "/usr/lib/python3/dist-packages/django/db/models/base.py", line 763, in save_base
    pre_save.send(
  File "/usr/lib/python3/dist-packages/django/dispatch/dispatcher.py", line 180, in send
    return [
  File "/usr/lib/python3/dist-packages/django/dispatch/dispatcher.py", line 181, in <listcomp>
    (receiver, receiver(signal=self, sender=sender, **named))
  File "/mnt/c/Dropbox/Parnasa/Web/wherewasit/backend/accounts/views.py", line 220, in your_model_pre_save
    old = UserInfo.objects.get(id=instance.id)
  File "/usr/lib/python3/dist-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/django/db/models/query.py", line 435, in get
    raise self.model.DoesNotExist(
accounts.models.UserInfo.DoesNotExist: UserInfo matching query does not exist.

原因分析 #

从异常栈可以明确，问题并非出在UserInfo.objects.create()本身，而是绑定在UserInfo模型上的pre_save信号接收器your_model_pre_save。

执行UserInfo.objects.create()时，Django会先触发pre_save信号，此时新的UserInfo对象还未写入数据库，instance.id（主键）尚未生成。但信号处理函数里直接执行了old = UserInfo.objects.get(id=instance.id)，尝试通过一个不存在的ID查询旧对象，必然会抛出UserInfo.DoesNotExist异常。

解决方法 #

修改your_model_pre_save信号处理函数，先判断当前对象是否为新建状态（即主键为空，还未保存到数据库），如果是则跳过查询旧对象的逻辑：

def your_model_pre_save(sender, instance, **kwargs):
    # 仅当对象已存在（主键不为空）时，才执行旧对象查询及后续逻辑
    if instance.pk is not None:
        old = UserInfo.objects.get(id=instance.id)
        # 原有的后续处理代码...

这样在创建新UserInfo时，就不会执行无效的查询操作，避免抛出异常。

内容的提问来源于stack exchange，提问作者AlwaysLearning