import wsgiref.handlers
import random
import logging
from google.appengine.ext import db
from google.appengine.ext import webapp
from xml.dom import minidom
# A simple sharded-counter.
class Counter(db.Model):
count = db.IntegerProperty(default=0)
@classmethod
def getCount(self):
total = 0
for counter in Counter.all():
total += counter.count
return total
@classmethod
def increment(self):
key_name = 'GD_Q__%d' % (random.randint(1, 10))
randomShard = Counter.get_or_insert(key_name=key_name)
def updateCounter(key):
shard = Counter.get(key)
shard.count += 1
shard.put()
db.run_in_transaction(updateCounter, randomShard.key())
# Model that stores Question information.
class Question(db.Model):
text = db.StringProperty(required=True)
yesCount = db.IntegerProperty(default=0)
totalCount = db.IntegerProperty(default=0)
randomValue = db.FloatProperty()
# Handler for 'GET' requests for a question.
class QuestionRequestHandler(webapp.RequestHandler):
def get(self):
self.response.headers['Content-Type'] = 'text/plain'
# Query for the number of questions which is stored in Counter table.
totalQuestions = Counter.getCount()
if(totalQuestions == 0):
self.response.out.write("NO_QUESTIONS")
return
randomSelection = random.random();
# Select the question with the largest 'randomValue' but within
# 'randomSelection'.
try:
question = Question.all().filter('randomValue <=', randomSelection).order('-randomValue').get()
# If randomSelection is too small, we just pick the first question.
# Warning: This strategy isn't fair on all questions.
if not question:
question = Question.all().get()
except db.Error:
self.response.out.write('DATABASE_ERROR')
self.response.out.write("%s\n%s\n" % (str(question.key()), question.text))
# Handler for 'POST' requests submitting a user's vote.
class VoteHandler(webapp.RequestHandler):
def post(self):
self.response.headers['Content-Type'] = 'text/plain'
voteStr = self.request.get('vote')
questionId = self.request.get('qid')
if not questionId or not voteStr:
self.response.out.write('INVALID_REQUEST')
return
vote = bool(int(voteStr))
def updateVote(key, vote):
question = Question.get(key)
if not question:
self.response.out.write('QUESTION_NOT_FOUND')
return
if vote:
question.yesCount += 1
question.totalCount += 1
question.put()
questionKey = db.Key(encoded=questionId)
db.run_in_transaction(updateVote, questionKey, vote)
self.response.out.write('OK')
# Handler for 'GET' requests for the top questions.
class TopQuestionsHandler(webapp.RequestHandler):
def get(self):
self.response.headers['Content-Type'] = 'text/plain'
numQuestions = self.request.get('num')
if not numQuestions:
numQuestions = 10
elif (numQuestions > 25):
numQuestions = 25
questions = Question.all().order("-totalCount").fetch(limit=numQuestions)
for question in questions:
noCount = question.totalCount - question.yesCount
self.response.out.write("%s\n%ld\n%ld\n\n" % (question.text, question.yesCount, noCount))
# Handler for home-page requests. The output of this handler is html as it
# should be accessible from a browser.
class HomePageHandler(webapp.RequestHandler):
def get(self):
self.response.headers['Content-Type'] = 'text/html'
questions = Question.all().order("-totalCount").fetch(limit=10)
self.response.out.write("""
Google Desktop Gadget Sample
""")
if len(questions) > 0:
self.response.out.write("""
|
Question |
+ve Votes |
-ve Votes |
""")
count = 1
for question in questions:
self.response.out.write("""
| %d |
%s |
%d |
%d |
""" % (count, question.text, question.yesCount, (question.totalCount - question.yesCount)))
count += 1
self.response.out.write("""
""")
# Handler that allows submission of new questions.
# TODO(yourself) Allow only logged-in users to post questions.
# TODO(yourself) All users except the admin should have an upper limit on the
# No. of questions one can submit.
class SubmitQuestionHandler(webapp.RequestHandler):
def post(self):
self.response.headers['Content-Type'] = 'text/plain'
questionText = self.request.get('question')
if not questionText:
self.response.out.write('INVALID_REQUEST')
question = Question(text=questionText)
question.randomValue = random.random()
question.put()
# GAE doesn't support transactions across entity groups. Hence, one of the 2 writes might not happen.
# Thus we write the question first so that in the worst-case, our count a bit lagging from the 'actual count'
# If the count is slightly less, the last few questions will not be displayed instantaneously.
# But that is okay.(better than 404s/retries that can be caused by incrementing the count first)
Counter.increment()
def main():
application = webapp.WSGIApplication(
[('/question', QuestionRequestHandler),
('/vote' , VoteHandler),
('/top', TopQuestionsHandler),
('/submit', SubmitQuestionHandler),
('/', HomePageHandler),
],
debug=True)
wsgiref.handlers.CGIHandler().run(application)
if __name__ == "__main__":
main()