gistfile1.py

#!/usr/bin/env python
# -*- coding: UTF-8 -*-

import sys
import re
import json

import tornado

import tornado.httpserver
import tornado.ioloop
import tornado.options
import tornado.web

from tornado import gen
from tornado.options import define, options

import motor

define("port", default=9090, help="dev port 9090", type=int)
define("host", default="localhost", help="dev host localhost only", type=str)

MONGO_URI   = "mongodb://localhost"


def motor_connection():
    return motor.MotorClient(MONGO_URI).open_sync().test_db

# this decorator catches exceptions of request handlers 
# and responds with a simple error page instead of sending Tornado traceback stack to the browser
def request_handler(method):
    def wrapper(self, *args, **kwargs):
        try:
            return method(self, *args, **kwargs)
        except:
            self.write("Error!")
    return wrapper
    
def prepare_to_json(doc):    
    doc["_id"] = str(doc["_id"])
    return doc

class MotorTesterRequestHandler(tornado.web.RequestHandler):

    @property
    def current_account(self):
        return self.get_current_account()

    @property
    def db(self):
        return self.settings['motor_db']
        
    def push_json(self, data):
        data = json.dumps(data)
        self.set_header('Content-Type', 'application/json')
        self.write(data)
        self.finish()


class TestHandler(MotorTesterRequestHandler):
    @request_handler
    def get(self):
        self.write("<h1>Hello World</h1>\n")

    @request_handler
    @gen.engine
    @tornado.web.asynchronous
    def post(self):        
        ga = self.get_argument
        data_filter = ga("filter")
        limit_number = int(ga("limit", 10))
        
        # toggle comment following pair of lines to see the issue
        # when providing {foo: data_filter} -- that's an error, as foo is not defined 
        # only timeout breaks.
        # cursor = self.db.sample_collection.find({foo: data_filter}).limit(limit_number)
        cursor = self.db.sample_collection.find({"foo": data_filter}).limit(limit_number)

        documents = yield motor.Op(cursor.to_list)
        
        self.push_json(map(prepare_to_json, documents))

class MotorApplication(tornado.web.Application):
    def __init__(self):

        settings = dict(
            autoescape=None,
            debug=True,
            motor_db = motor_connection()
        )

        # paths which available for ui client only.
        url_mapper = [
            (r"/", TestHandler),

        ]

        tornado.web.Application.__init__(self, url_mapper, **settings)

def main():
    tornado.options.parse_command_line()

    console_server = tornado.httpserver.HTTPServer(MotorApplication())
    console_server.listen(options.port, options.host)

    tornado.ioloop.IOLoop.instance().start()


if __name__ == "__main__":
    main()

# prepare DB
mongo> use test_db
mongo> db.sample_collection.insert({foo:"1"})
mongo> db.sample_collection.find()
{ "_id" : ObjectId("516b8dd1c3a5397d1469d152"), "foo" : "1" }

# test the server
$ curl localhost:9090 --data filter=2
[]
$ curl localhost:9090 --data filter=1
[{"_id": "516b8dd1c3a5397d1469d152", "foo": "1"}

The problem:

Toggle comment lines 76-77 and see no error for calling find with {foo: data_filter} instead of {"foo": data_filter}.

cursor = self.db.sample_collection.find({foo: data_filter}).limit(limit_number)
# cursor = self.db.sample_collection.find({"foo": data_filter}).limit(limit_number)