GAE datastore does not refresh

StackOverflow https://stackoverflow.com/questions/16022165

Question

When i update the GAE datastore, only after a browser refresh of the page the correct datastore contents is shown:

import os

from google.appengine.ext.webapp import template
from google.appengine.ext import db
import webapp2

#def testkey():
#  return db.Key.from_path('test', 'test')

class TestEntity(db.Model):
  testkey = db.StringProperty(multiline=False)
  testvalue = db.StringProperty(multiline=False)

class TestRefreshProblem(webapp2.RequestHandler):
  def get(self):
    testquery = TestEntity.all()#.ancestor(testkey())
    entities = testquery.run()
    template_values = {
      'entities': entities,
      }
    path = os.path.join(os.path.dirname(__file__), 'index.html')
    self.response.out.write(template.render(path, template_values))

class TestRefreshProblemPost(webapp2.RequestHandler):
  def post(self):
    # testEntity = TestEntity(parent=testkey())
    testEntity = TestEntity()
    testEntity.testkey = self.request.get('testkey')
    testEntity.testvalue = self.request.get('testvalue')
    testEntity.put()
    self.redirect('/')

app = webapp2.WSGIApplication([
    ('/', TestRefreshProblem),
    ('/pst', TestRefreshProblemPost)
], debug=True)

and index.html is:

<html>
  <body>
    <table border=0>
        <tr><td width=200>Key</td><td width=200>Value</td></tr>
        {% for entity in entities %}
          <tr>
            <td width=200>{{ entity.testkey|escape }}</td>
            <td width=200>{{ entity.testvalue|escape }}</td>
          </tr>
        {% endfor %}
      </table>
     <form action="/pst" method="post">
      <table>
        <td ><input type="text" name="testkey" size=30/></td>
        <td ><input type="text" name="testvalue" size=30/></td>
        <tr><td><input type="submit" value="Add entity"></td></tr>
      </table>
    </form>
  </body>
</html>

The problem disappears by using a (dummy) ancestor (re: the lines with a #). It seems to me to be strange behaviour ... Can it be solved without an ancestor?

Was it helpful?

Solution

This is expected behavior because of eventual consistency.

Actually, because you are running the development server, this is only a simulation of eventual consistency - in the real production system, the results won't be quite as predictable. The solution is the same though.

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