In Twisted there is a great thing known as `ContextTracker`:
> provides a way to pass arbitrary key/value data up and down a call
> stack without passing them as parameters to the functions on that call
> stack.
In my twisted web app in method `render_GET` I set a `uuid` parameter:
call = context.call({"uuid": str(uuid.uuid4())}, self._render, request)
and then I call the `_render` method to do the actual work (work with db,
render html, etc).
I create the `scoped_session` like this:
scopefunc = functools.partial(context.get, "uuid")
Session = scoped_session(session_factory, scopefunc=scopefunc)
Now within any function calls of `_render` I can get session with:
Session()
and at the end of `_render` I have to do `Session.remove()` to remove the
session.
It works with my webapp and I think can work for other tasks.
This is completely standalone example, show how all it work together.
from twisted.internet import reactor, threads
from twisted.web.resource import Resource
from twisted.web.server import Site, NOT_DONE_YET
from twisted.python import context
from sqlalchemy import create_engine, Column, Integer, String
from sqlalchemy.orm import sessionmaker, scoped_session
from sqlalchemy.ext.declarative import declarative_base
import uuid
import functools
engine = create_engine(
'sqlite:///test.sql',
connect_args={'check_same_thread': False},
echo=False)
session_factory = sessionmaker(bind=engine)
scopefunc = functools.partial(context.get, "uuid")
Session = scoped_session(session_factory, scopefunc=scopefunc)
Base = declarative_base()
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)
Base.metadata.create_all(bind=engine)
class TestPage(Resource):
isLeaf = True
def render_GET(self, request):
context.call({"uuid": str(uuid.uuid4())}, self._render, request)
return NOT_DONE_YET
def render_POST(self, request):
return self.render_GET(request)
def work_with_db(self):
user = User(name="TestUser")
Session.add(user)
Session.commit()
return user
def _render(self, request):
print "session: ", id(Session())
d = threads.deferToThread(self.work_with_db)
def success(result):
html = "added user with name - %s" % result.name
request.write(html.encode('UTF-8'))
request.finish()
Session.remove()
call = functools.partial(context.call, {"uuid": scopefunc()},
success)
d.addBoth(call)
return d
if __name__ == "__main__":
reactor.listenTCP(8888, Site(TestPage()))
reactor.run()
Still I dont know how to make it work with `defer.inLineCallback`, that I
use everywhere in my code.
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