I am new to Sanic and I am trying to get it to work with Motor. I did manage to get everything to work in a single file, however, when I try it out within my project structure, I am running into the below issues.
[2018-02-28 17:26:58 +0530] [3720] [ERROR] Traceback (most recent call
last):
File "/usr/local/lib/python3.6/site-packages/sanic/app.py", line 556, in
handle_request
response = await response
File "/usr/src/Python-3.6.4/Lib/asyncio/coroutines.py", line 129, in throw
return self.gen.throw(type, value, traceback)
File "/home/msambare/Documents/Projects/Snippets/Sanic-Motor-
Issue/IAC/src/MyPackgae/REST/user_REST.py", line 42, in post
request.json['last']
File "/usr/src/Python-3.6.4/Lib/asyncio/coroutines.py", line 129, in throw
return self.gen.throw(type, value, traceback)
File "/home/msambare/Documents/Projects/Snippets/Sanic-Motor-
Issue/IAC/src/MyPackgae/DAO/user_DAO.py", line 40, in register_user
result = await db.users.insert_one(serialized_user)
RuntimeError: Task <Task pending coro=<Sanic.handle_request() running at
/usr/local/lib/python3.6/site-packages/sanic/app.py:556> created at
/usr/local/lib/python3.6/site-packages/sanic/server.py:299> got Future
<Future pending cb=[run_on_executor.<locals>._call_check_cancel() at
/usr/local/lib/python3.6/site-
packages/motor/frameworks/asyncio/__init__.py:85]> attached to a different
loop
I did some research and as mentioned on the GitHub pages of Sanic, tried the 'before-server-block' section for db setup. That works in a single file, however, not in my project structure.
My project structure looks something like:
Below is my code. I have recreated the issue in a simpler structure without losing the essence.
src/MyPackage/Model/user.py
class User(object):
def __init__(self, first, last):
self.first = first
self.last = last
src/MyPackage/UC/user_uc.py
from Model import User
from DAO import User_DAO
class User_UC(object):
def __init__(self):
self._user = None
def create_user(self, first, last):
self._user = User(first, last)
ud = User_DAO()
id = ud.register_user(
{
'first': first,
'last': last
}
)
return id
src/DAO/motor_connection.py
import uvloop
import asyncio
import motor.motor_asyncio
asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())
class Motor_Connection(object):
""" Provides a MongoDB connection and sets the DB to be used.
The class implements the Singleton pattern.
"""
__instance = None
def __new__(cls):
if Motor_Connection.__instance is None:
Motor_Connection.__instance = object.__new__(cls)
Motor_Connection.__instance.client = \
motor.motor_asyncio.AsyncIOMotorClient(
'localhost',
27017,
io_loop=asyncio.get_event_loop()
)
Motor_Connection.__instance.db = \
Motor_Connection.__instance.client.test_database
return Motor_Connection.__instance.db
src/DAO/user_DAO.py
from DAO import Motor_Connection
db = Motor_Connection()
class User_DAO(object):
async def register_user(self, serialized_user):
result = await db.users.insert_one(serialized_user)
return result.inserted_id
src/MyPackage/REST/user_REST.py
from sanic.views import HTTPMethodView
from sanic.response import text
from UC import User_UC
class User_REST(HTTPMethodView):
async def post(self, request):
user_uc = User_UC()
id = await user_uc.create_user(
request.json['first'],
request.json['last']
)
return text(id)
and finally the main program...
src/MyPackage/main.py
from sanic import Sanic
from DAO import Motor_Connection
from REST import User_REST
app = Sanic()
@app.listener('before_server_start')
def init(sanic, loop):
global db
db = Motor_Connection()
app.add_route(User_REST.as_view(), '/')
if __name__ == "__main__":
app.run(host="0.0.0.0", port=8000, workers=3, debug=True)
I have not included the init.py files of any of the sub-packages. The only thing that I have done in those files is bringing the classes to the sub-package level.
From what I have been able to figure out, it seems in main.py when the User_Rest class is imported which in turn imports the User_UC class which imports the User_DAO class which in turn imports the Motor_Connection class - this is where the mess happens. This creates a separate event loop which is not shared by Sanic.
So, if my understanding is correct, all the chained imported classes use one event loop and Sanic uses another event loop. I know we cannot have 2 event loops but I am unable to figure out what needs to be done to sort this out.
Please help. Thanks in advance.
Ok. The issue is resolved. I had to use global variables to resolve it. Please find the modified code below for reference.
main.py
from sanic import Sanic
from DAO import Motor_Connection
from REST import User_REST
import commons
app = Sanic()
@app.listener('before_server_start')
def init(sanic, loop):
commons.db = Motor_Connection()
app.add_route(User_REST.as_view(), '/')
if __name__ == "__main__":
app.run(host="0.0.0.0", port=8000, workers=3, debug=True)
commons.globals.py
db = None
user_DAO.py
import commons
class User_DAO(object):
async def register_user(self, serialized_user):
result = await commons.db.users.insert_one(serialized_user)
return result.inserted_id
Explanation: While the motor connection class was a singleton and returned the same instance, as it was initialized during the imports, Sanic could not get a handle on the event loop. Sanic has to be initialized first to be able to get a handle on the event loop.
By using a global variable and initializing it in the before_server_start block, Sanic gets the handle. Now when you use the same variable in the DAO class, you have access to Sanic's event loop.