Question

I want to use nose to test an application that I am writing using twisted and txmongo. I can’t even get simple use cases like the following working:
from nose.twistedtools import reactor, deferred, threaded_reactor
import logging
from twisted.internet import defer
import txmongo

log = logging.getLogger("common.test.test_db")

conn = txmongo.lazyMongoConnectionPool('localhost', 27017, 4)

@deferred()
def test_mongo():
    tdb = conn.test

    @defer.inlineCallbacks
    def cb(oid):
        assert oid
        obj = yield tdb.test.find({"_id":oid})
        log.error("In callback")
        assert obj 

    d = tdb.test.save({"s":1, "b":2})
    d.addCallback(cb)

    return d

However, this always return the following:

E
======================================================================
ERROR: common.test.test_db.test_mongo
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Volumes/Users/jce/.pyenv/celery/lib/python2.6/site-packages/nose/case.py", line 186, in runTest
    self.test(*self.arg)
  File "/Volumes/Users/jce/.pyenv/celery/lib/python2.6/site-packages/nose/twistedtools.py", line 138, in errback
    failure.raiseException()
  File "/Volumes/Users/jce/.pyenv/celery/lib/python2.6/site-packages/twisted/python/failure.py", line 326, in raiseException
    raise self.type, self.value, self.tb
RuntimeWarning: not connected

----------------------------------------------------------------------
Ran 1 test in 0.006s

FAILED (errors=1)

I tried manually adding a threaded_reactor() call, but it didn’t help.

edit

I removed the “lazy” connections, and modified the code, and now it works… I’m still curious as to why the “lazy” didn’t work. The working code is as follows:

dbconn = txmongo.MongoConnectionPool('localhost', 27017, 4)

@deferred()
def test_mongo():
    @defer.inlineCallbacks
    def cb(conn):
        tdb = conn.test
        oid = yield tdb.test.save({"s":1, "b":2})
        assert oid
        log.error(str(oid))
        obj = yield tdb.test.find({"_id":oid})
        assert obj 
        log.error(str(obj))
    dbconn.addCallback(cb)
    return dbconn

Answer 1

MongoConnectionPool will return a deferred, which is fired when the connection is established passing the connection handler as argument to the callback. You should conn = yield MongoConnectionPool().

lazyMongoConnectionPool will return the connection handler directly, without waiting for the connection to be established.

Lazy is usually used by web servers and other services that doesn’t require immediate connection when your service starts. If you want to do so, don’t use the lazy method.