ContextError when using @ndb.transactional()

[timlichen]

Environment details

ndb version: 0.1.0

Code example

 @staticmethod
 @ndb.transactional()
 def test_func():
 ModelName.query().get()

Stack trace

Traceback (most recent call last):
 File "/Users/timchen/.virtualenvs/pyenv3/lib/python3.7/site-packages/gunicorn/workers/sync.py", line 135, in handle
 self.handle_request(listener, req, client, addr)
 File "/Users/timchen/.virtualenvs/pyenv3/lib/python3.7/site-packages/gunicorn/workers/sync.py", line 176, in handle_request
 respiter = self.wsgi(environ, resp.start_response)
 File "/Users/timchen/.virtualenvs/pyenv3/lib/python3.7/site-packages/flask/app.py", line 2309, in __call__
 return self.wsgi_app(environ, start_response)
 File "/Users/timchen/Projects/project/utils/custom_middleware.py", line 12, in __call__
 return self.app(environ, start_response)
 File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/contextlib.py", line 119, in __exit__
 next(self.gen)
 File "/Users/timchen/.virtualenvs/pyenv3/lib/python3.7/site-packages/google/cloud/ndb/client.py", line 176, in context
 context.eventloop.run()
 File "/Users/timchen/.virtualenvs/pyenv3/lib/python3.7/site-packages/google/cloud/ndb/_eventloop.py", line 355, in run
 if not self.run1():
 File "/Users/timchen/.virtualenvs/pyenv3/lib/python3.7/site-packages/google/cloud/ndb/_eventloop.py", line 344, in run1
 delay = self.run0()
 File "/Users/timchen/.virtualenvs/pyenv3/lib/python3.7/site-packages/google/cloud/ndb/_eventloop.py", line 313, in run0
 if self._run_current() or self.run_idle():
 File "/Users/timchen/.virtualenvs/pyenv3/lib/python3.7/site-packages/google/cloud/ndb/_eventloop.py", line 278, in run_idle
 result = callback(*args, **kwargs)
 File "/Users/timchen/.virtualenvs/pyenv3/lib/python3.7/site-packages/google/cloud/ndb/_batch.py", line 62, in idle
 batch.idle_callback()
 File "/Users/timchen/.virtualenvs/pyenv3/lib/python3.7/site-packages/google/cloud/ndb/_cache.py", line 67, in idle_callback
 cache_call = self.make_call()
 File "/Users/timchen/.virtualenvs/pyenv3/lib/python3.7/site-packages/google/cloud/ndb/_cache.py", line 261, in make_call
 cache = context_module.get_context().global_cache
 File "/Users/timchen/.virtualenvs/pyenv3/lib/python3.7/site-packages/google/cloud/ndb/context.py", line 65, in get_context
 raise exceptions.ContextError()
google.cloud.ndb.exceptions.ContextError: No current context. NDB calls must be made in context established by google.cloud.ndb.Client.context.

We are running this in a Flask application with custom middleware to instantiate client context. Calls made without transactional decorator work properly. We've tried decorating class, static, instance and standalone functions as well as closures with no success all resulting in the same traceback.

[chrisrossi]

Thanks for this report. I'll take a look.

[chrisrossi]

Hi, I'm not able reproduce this problem. I've attached a simple Flask app I've used to test. Please verify this isn't a bug in your application code, or modify my example to expose the bug in NDB.

import flask
import pprint

from google.cloud import ndb


def ndb_wsgi_middleware(wsgi_app):
 def middleware(environ, start_response):
 with client.context():
 return wsgi_app(environ, start_response)

 return middleware


client = ndb.Client()
app = flask.Flask("Test #213")
app.wsgi_app = ndb_wsgi_middleware(app.wsgi_app) # Wrap the app in middleware.


class SomeThing(ndb.Model):
 foo = ndb.StringProperty()

 @staticmethod
 @ndb.transactional()
 def first():
 return SomeThing.query().get()


@app.route("/")
def show_a_thing():
 thing = SomeThing.first()
 return text(thing_json(thing))


def thing_json(thing):
 return {
 "key": thing.key,
 "properties": thing.to_dict(),
 }


def text(s, status=200):
 if not isinstance(s, str):
 s = pprint.pformat(s)

 return s + "\n", status, {
 "Content-type": "text/plain; charset=utf-8",
 }

[epluntze]

I was able to reproduce the error by modifying your example to be a bit more like our running application. We are using flask MethodView and a custom NDBMiddleware class that creates the context through an overridden __call__. it also attempts to make use of the global cache if it's present. There is no environment variable to supply the global cache in this example but we make use of it in our full app

from flask import Flask, Blueprint
from flask.views import MethodView
from user import User

from google.cloud import ndb

class NDBMiddleware:
 def __init__(self, app):
 self.global_cache = ndb.RedisCache.from_environment()
 self.app = app
 self.client = ndb.Client()

 def __call__(self, environ, start_response):
 with self.client.context(global_cache=self.global_cache):
 return self.app(environ, start_response)


class AdminLogin(MethodView):
 def get(self):

 @ndb.transactional(retries=2)
 def get_user():
 user = User.query().get()
 user.put()
 return user

 print(get_user())
 return '', 200


def create_admin_app():
 app = Flask(__name__)
 app.wsgi_app = NDBMiddleware(app.wsgi_app)
 admin_blueprint = Blueprint('admin', __name__,
 url_prefix='/admin',)

 admin_login_view = AdminLogin.as_view('admin_login')
 admin_blueprint.add_url_rule('/', view_func=admin_login_view,
 methods=['GET', ], endpoint='admin_login')

 app.register_blueprint(admin_blueprint, url_prefix='/admin')
 return app


test = create_admin_app()

[chrisrossi]

I'm still having trouble reproducing this. Here is the example above reworked so that it can actually be run:

from flask import Flask, Blueprint
from flask.views import MethodView

from google.cloud import ndb


class User(ndb.Model):
 name = ndb.StringProperty()


class NDBMiddleware:
 def __init__(self, app):
 self.global_cache = ndb.RedisCache.from_environment()
 self.app = app
 self.client = ndb.Client()

 def __call__(self, environ, start_response):
 with self.client.context(global_cache=self.global_cache):
 return self.app(environ, start_response)


class AdminLogin(MethodView):
 def get(self):

 @ndb.transactional(retries=2)
 def get_user():
 user = User.query().get()
 user.put()
 return user

 user = get_user()
 return f"Hi {user.name}!\n", 200


def create_admin_app():
 app = Flask(__name__)
 app.wsgi_app = NDBMiddleware(app.wsgi_app)
 admin_blueprint = Blueprint('admin', __name__,
 url_prefix='/admin',)

 admin_login_view = AdminLogin.as_view('admin_login')
 admin_blueprint.add_url_rule('/', view_func=admin_login_view,
 methods=['GET', ], endpoint='admin_login')

 app.register_blueprint(admin_blueprint, url_prefix='/admin')
 return app


test = create_admin_app()


@test.route("/init")
def make_user():
 user = User(name="Fred")
 user.put()
 return "OK\n", 200

I stand up the test app like so:

(flask-ndb) chris@opportunity:~/proj/google/flask-ndb$ FLASK_APP=transactional-bug:test flask run
 * Serving Flask app "transactional-bug:test"
 * Environment: production
 WARNING: This is a development server. Do not use it in a production deployment.
 Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
127.0.0.1 - - [02/Oct/2019 14:50:59] "GET /admin/ HTTP/1.1" 200 -

And here is the result:

chris@opportunity:~/proj/google/flask-ndb$ curl http://localhost:5000/admin/
Hi Fred!

Can you expose the bug in a single file app that is runnable on its own?

[epluntze]

Ok, I re-ran your code and I was still getting the error so I looked into my config and environment variables. Turns out I was using global cache via ndb.RedisCache.from_environment() as I had copied my config from my main project

I have a Redis instance running on localhost:6379 and the environment variable REDIS_CACHE_URL=redis://localhost:6379/0 is set

When I set self.global_cache to None it worked with no issue, but with global cache enabled I'm getting the context error consistently

[chrisrossi]

Ah! Ok. That's interesting. Thank you.

[epluntze]

Here is how I am starting the app to trigger the error

(py_37) Erics-MacBook-Pro:ndb_test eric$ REDIS_CACHE_URL=redis://localhost:6379/0 gunicorn -b :8081 test_app:test
[2019-10-02 16:29:22 -0400] [44412] [INFO] Starting gunicorn 19.9.0
[2019-10-02 16:29:22 -0400] [44412] [INFO] Listening at: http://0.0.0.0:8081 (44412)
[2019-10-02 16:29:22 -0400] [44412] [INFO] Using worker: sync
[2019-10-02 16:29:22 -0400] [44415] [INFO] Booting worker with pid: 44415
/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/google/auth/_default.py:66: 
redis://localhost:6379/0
[2019-10-02 16:29:25 -0400] [44415] [ERROR] Error handling request /admin/
Traceback (most recent call last):
 File "/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/gunicorn/workers/sync.py", line 135, in handle
 self.handle_request(listener, req, client, addr)
 File "/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/gunicorn/workers/sync.py", line 176, in handle_request
 respiter = self.wsgi(environ, resp.start_response)
 File "/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/flask/app.py", line 2309, in __call__
 return self.wsgi_app(environ, start_response)
 File "/Users/eric/Projects/sandboxx/ndb_test/test_app.py", line 19, in __call__
 return self.app(environ, start_response)
 File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/contextlib.py", line 119, in __exit__
 next(self.gen)
 File "/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/google/cloud/ndb/client.py", line 176, in context
 context.eventloop.run()
 File "/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/google/cloud/ndb/_eventloop.py", line 355, in run
 if not self.run1():
 File "/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/google/cloud/ndb/_eventloop.py", line 344, in run1
 delay = self.run0()
 File "/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/google/cloud/ndb/_eventloop.py", line 313, in run0
 if self._run_current() or self.run_idle():
 File "/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/google/cloud/ndb/_eventloop.py", line 278, in run_idle
 result = callback(*args, **kwargs)
 File "/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/google/cloud/ndb/_batch.py", line 62, in idle
 batch.idle_callback()
 File "/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/google/cloud/ndb/_cache.py", line 67, in idle_callback
 cache_call = self.make_call()
 File "/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/google/cloud/ndb/_cache.py", line 261, in make_call
 cache = context_module.get_context().global_cache
 File "/Users/eric/Projects/sandboxx/py_37/lib/python3.7/site-packages/google/cloud/ndb/context.py", line 65, in get_context
 raise exceptions.ContextError()
google.cloud.ndb.exceptions.ContextError: No current context. NDB calls must be made in context established by google.cloud.ndb.Client.context.

and to trigger:

Erics-MacBook-Pro: eric$ curl http://localhost:8081/admin/
<html>
 <head>
 <title>Internal Server Error</title>
 </head>
 <body>
 <h1><p>Internal Server Error</p></h1>

 </body>
</html>

and Redis is running on 6379

Erics-MacBook-Pro: eric$ redis-cli
127.0.0.1:6379>

[chrisrossi]

I can now reproduce. Thanks. I'll take a look.