paging/suggestunique.py

   1 #!/usr/bin/env python
   2 #
   3 # Copyright 2008 Google Inc.
   4 #
   5 # Licensed under the Apache License, Version 2.0 (the "License");
   6 # you may not use this file except in compliance with the License.
   7 # You may obtain a copy of the License at
   8 #
   9 #     http://www.apache.org/licenses/LICENSE-2.0
  10 #
  11 # Unless required by applicable law or agreed to in writing, software
  12 # distributed under the License is distributed on an "AS IS" BASIS,
  13 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14 # See the License for the specific language governing permissions and
  15 # limitations under the License.
  16 #
  17
  18 """Suggestion Box - An example paging application.
  19
  20 A simple Suggestion Box application that demonstrates
  21 paging by creating a unique value for each suggestion. The
  22 uniqueness is created by sharding counters across
  23 all the users of the system.
  24
  25 """
  26
  27 import datetime
  28 import hashlib
  29 import os
  30 import wsgiref.handlers
  31
  32 from google.appengine.ext import webapp
  33 from google.appengine.ext.webapp import template
  34 from google.appengine.ext import db
  35 from google.appengine.api import users
  36 from google.appengine.ext.webapp.util import login_required
  37 from google.appengine.ext.webapp.util import run_wsgi_app
  38
  39
  40 PAGESIZE = 5
  41
  42
  43 class Contributor (db.Model):
  44   """
  45   Contributors are stored with a key of the users email
  46   address. The 'count' is used as a per user
  47   counter that is incremented each time a user
  48   adds a Suggestion and is used to generate a unique
  49   property value 'Suggestion.when' that allows paging
  50   over suggestions in creation order.
  51   """
  52   count = db.IntegerProperty(default=0)
  53
  54
  55 class Suggestion(db.Model):
  56   """
  57   A suggestion in the suggestion box, which we want to display
  58   in the order they were created.
  59   """
  60   suggestion = db.StringProperty()
  61   created = db.DateTimeProperty(auto_now_add=True)
  62   when = db.StringProperty()
  63
  64
  65 def _unique_user(user):
  66   """
  67   Creates a unique string by using an increasing
  68   counter sharded per user. The resulting string
  69   is hashed to keep the users email address private.
  70
  71   Args:
  72      The currently logged in user.
  73
  74   Returns:
  75      A hashed unique value based on the user
  76      and the associated incremented Contributor.count.
  77   """
  78   email = user.email()
  79
  80   def txn():
  81     contributor = Contributor.get_by_key_name(email)
  82     if contributor == None:
  83       contributor = Contributor(key_name=email)
  84     contributor.count += 1
  85     contributor.put()
  86     return contributor.count
  87
  88   count = db.run_in_transaction(txn)
  89
  90   return hashlib.md5(email + '|' + str(count)).hexdigest()
  91
  92
  93 def whenfromcreated(created):
  94   """
  95   Create a unique 'when' property value based on the
  96   time the entity was created.
  97
  98   Args:
  99     created:  datetime the entity was created.
 100
 101   Returns:
 102     A unique value that will be ordered by
 103     entity creation time.
 104   """
 105   return created.isoformat()[0:19] + '|' + _unique_user(users.get_current_user())
 106
 107
 108 class SuggestionHandler(webapp.RequestHandler):
 109   """
 110   Handles the creation of a single Suggestion, and the display
 111   of suggestions broken into PAGESIZE pages.
 112   """
 113
 114   @login_required
 115   def get(self):
 116     bookmark = self.request.get('bookmark')
 117     next = None
 118     if bookmark:
 119       query = Suggestion.gql('WHERE when <= :bookmark ORDER BY when DESC',
 120         bookmark=bookmark)
 121       suggestions = query.fetch(PAGESIZE+1)
 122     else:
 123       suggestions = Suggestion.gql('ORDER BY when DESC').fetch(PAGESIZE+1)
 124     if len(suggestions) == PAGESIZE+1:
 125       next = suggestions[-1].when
 126       suggestions = suggestions[:PAGESIZE]
 127
 128     template_values = {'next': next, 'suggestions': suggestions}
 129     template_file = os.path.join(os.path.dirname(__file__), 'suggestion.html')
 130     self.response.out.write(template.render(template_file, template_values))
 131
 132   def post(self):
 133     now = datetime.datetime.now()
 134     when = whenfromcreated(now)
 135     s = Suggestion(
 136       suggestion = self.request.get('suggestion'),
 137       when=when,
 138       created=now)
 139     s.put()
 140
 141     self.redirect('/unique/')
 142
 143
 144 class SuggestionPopulate(webapp.RequestHandler):
 145   def post(self):
 146     now = datetime.datetime.now()
 147     for i in range(6):
 148       s = Suggestion(
 149         suggestion = 'Suggestion %d' % i,
 150         created = now,
 151         when = whenfromcreated(now))
 152       s.put()
 153
 154     self.redirect('/unique/')
 155
 156
 157 def main():
 158   application = webapp.WSGIApplication([
 159     ('/unique/pop/', SuggestionPopulate),
 160     ('/unique/', SuggestionHandler)
 161   ], debug=True)
 162   wsgiref.handlers.CGIHandler().run(application)
 163
 164
 165 if __name__ == '__main__':
 166   main()