asynchronous - Django : SynchronousOnlyOperation: You cannot call this from an async context - use a thread or sync_to_async

Question

我使用 Django 3.0.6 和 Jupyter notebook 运行 shell_plus --notebook .

我尝试运行查询集:
User.objects.all()
但是返回这个错误SynchronousOnlyOperation: You cannot call this from an async context - use a thread or sync_to_async .

我试试这个命令

from asgiref.sync import sync_to_async

users = sync_to_async(User.objects.all())

for user in users:
    print(user)

TypeError: 'SyncToAsync' object is not iterable

Django文档的解决方案
os.environ["DJANGO_ALLOW_ASYNC_UNSAFE"] = "true"在 settings.py 中是唯一的解决方案吗？

Answer 1

sync_to_async需要一个可调用的，而不是结果。相反，你想要这个:

from asgiref.sync import sync_to_async

users = sync_to_async(User.objects.all)()

for user in users:
    print(user)

您还可以将要包装的调用放入装饰函数中:

from asgiref.sync import sync_to_async

@sync_to_async
def get_all_users():
    return User.objects.all()

for user in await get_all_users():
    print(user)

请注意，这必须在异步上下文中使用，因此完整示例如下所示:

from asgiref.sync import sync_to_async

@sync_to_async
def get_all_users():
    return User.objects.all()

async def foo(request):
    for user in await get_all_users():
        print(user)

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