[PR 8617 - Async implementation] Async exception when returning Response(Serializer(instance).data)

[dongyuzheng]

You cannot call this from an async context - use a thread or sync_to_async.

For PR #8617

1. Make async function-based api_view return Response(Serializer(instance).data)
2. Hit API (POST in my example)

SynchronousOnlyOperation at /api/create_user
You cannot call this from an async context - use a thread or sync_to_async.

Request Method: POST
Request URL: http://0.0.0.0:8000/api/create_user
Django Version: 4.1.1
Python Executable: /usr/local/bin/python3.10
Python Version: 3.10.7
Python Path: ['.', '/usr/local/bin', '/code', '/code/bb_backend', '/usr/local/lib/python310.zip', '/usr/local/lib/python3.10', '/usr/local/lib/python3.10/lib-dynload', '/root/.local/lib/python3.10/site-packages', '/usr/local/lib/python3.10/site-packages']
Server time: Sun, 18 Sep 2022 06:16:30 +0000
Installed Applications:
['django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'rest_framework',
 '<my_app>',
 'corsheaders']
Installed Middleware:
['corsheaders.middleware.CorsMiddleware',
 'django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']


Traceback (most recent call last):
  File "/usr/local/lib/python3.10/site-packages/asgiref/sync.py", line 472, in thread_handler
    raise exc_info[1]
  File "/usr/local/lib/python3.10/site-packages/django/core/handlers/exception.py", line 42, in inner
    response = await get_response(request)
  File "/usr/local/lib/python3.10/site-packages/django/core/handlers/base.py", line 253, in _get_response_async
    response = await wrapped_callback(
  File "/usr/local/lib/python3.10/site-packages/rest_framework/views.py", line 539, in async_dispatch
    response = self.handle_exception(exc)
  File "/usr/local/lib/python3.10/site-packages/rest_framework/views.py", line 469, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/usr/local/lib/python3.10/site-packages/rest_framework/views.py", line 480, in raise_uncaught_exception
    raise exc
  File "/usr/local/lib/python3.10/site-packages/rest_framework/views.py", line 536, in async_dispatch
    response = await handler(request, *args, **kwargs)
  File "/usr/local/lib/python3.10/site-packages/rest_framework/decorators.py", line 54, in async_handler
    return await func(*args, **kwargs)
  File "/code/bb_backend/./bb_core/api/auth.py", line 55, in create_user
    return Response(UserSerializer(instance=user).data)
  File "/usr/local/lib/python3.10/site-packages/rest_framework/serializers.py", line 555, in data
    ret = super().data
  File "/usr/local/lib/python3.10/site-packages/rest_framework/serializers.py", line 253, in data
    self._data = self.to_representation(self.instance)
  File "/usr/local/lib/python3.10/site-packages/rest_framework/serializers.py", line 522, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "/usr/local/lib/python3.10/site-packages/rest_framework/relations.py", line 565, in to_representation
    return [
  File "/usr/local/lib/python3.10/site-packages/django/db/models/query.py", line 394, in __iter__
    self._fetch_all()
  File "/usr/local/lib/python3.10/site-packages/django/db/models/query.py", line 1866, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "/usr/local/lib/python3.10/site-packages/django/db/models/query.py", line 87, in __iter__
    results = compiler.execute_sql(
  File "/usr/local/lib/python3.10/site-packages/django/db/models/sql/compiler.py", line 1393, in execute_sql
    cursor = self.connection.cursor()
  File "/usr/local/lib/python3.10/site-packages/django/utils/asyncio.py", line 24, in inner
    raise SynchronousOnlyOperation(message)

Exception Type: SynchronousOnlyOperation at /api/create_user
Exception Value: You cannot call this from an async context - use a thread or sync_to_async.

[ahzamm]

@dongyuzheng is this issue still open or resolved?

[tomchristie]

Closing as per #8655