CODEWITHSUNDEEP
pythongoogle-app-engine
billwild
billwild

Reputation: 173

Reloading the page

I'm very new to google app engine and i'm trying this guestbook google code example. What is my problem is when i post a post it doesn't displays it but when i post the second post it displays the first post. It seems like the page is needed to be refreshed at the first time and seems like this code "self.redirect('/')" work a step back ahead of the program. Or there is a different problem please help me. I don't know if this is about my computer but i would be appreciated if you could help me.

And here is the original code:

import cgi
import os

from google.appengine.api import users
from google.appengine.ext import webapp
from google.appengine.ext.webapp.util import run_wsgi_app
from google.appengine.ext import db
from google.appengine.ext.webapp import template

class Greeting(db.Model):
  author = db.UserProperty()
  content = db.StringProperty(multiline=True)
  date = db.DateTimeProperty(auto_now_add=True)

class MainPage(webapp.RequestHandler):
  def get(self):
    greetings_query = Greeting.all().order('-date')
    greetings = greetings_query.fetch(10)

    if users.get_current_user():
      url = users.create_logout_url(self.request.uri)
      url_linktext = 'Logout'
    else:
      url = users.create_login_url(self.request.uri)
      url_linktext = 'Login'

    template_values = {
      'greetings': greetings,
      'url': url,
      'url_linktext': url_linktext,
      }

    path = os.path.join(os.path.dirname(__file__), 'index.html')
    self.response.out.write(template.render(path, template_values))


class Guestbook(webapp.RequestHandler):
  def post(self):
    greeting = Greeting()

    if users.get_current_user():
      greeting.author = users.get_current_user()

    greeting.content = self.request.get('content')
    greeting.put()
    self.redirect('/')

application = webapp.WSGIApplication(
                                     [('/', MainPage),
                                      ('/sign', Guestbook)],
                                     debug=True)

def main():
  run_wsgi_app(application)

if __name__ == "__main__":
  main()

Upvotes: 0

Views: 102

Answers (1)

Adam Crossland
Adam Crossland

Reputation: 14213

I don't see that there is anything wrong with this code, so I am inclined to think that your browser may be caching the main page and so displaying results without actually making a call to your AppEngine site. I'd suggest modifying the redirect by adding a parameter at the end of the URL that will cause your browser to make a call to the server. Here's an approach:

Add import time to the imports at the top of the file.

Change the end of the post method of Guestbook to read:

timestamp = str(time.time()).replace(".","")
self.redirect('/?cachebuster=' + timestamp)

The GET query parameter value that is added to the URL will make sure that your browser makes a new actual request to the server.

EDIT: Silly me. I think that what you are seeing is the effect of eventual consistency. In short: Google's High-replication Datastore stores your app's data in multiple datacenters, but you have to take special measures to guarantee that when you do a query that you get strongly consistent results; otherwise, the datacenter that serves your query might not have received the update with the new data yet.

It is all very well documented in the AppEngine Developer Docs: https://developers.google.com/appengine/docs/python/datastore/structuring_for_strong_consistency

Upvotes: 1

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