Practice 7 - Google App Engine continued

In this practice session we will continue with Google App engine. You will learn how to store arbitrary objects in the Google data store service and extend the last week solution by creating a new web page in your application where users can leave and read messages.

References

Referred documents and web sites contain supportive information for the practice.

• Python 2.7 tutorial
• Google App Engine tutorial for Python 2.7
• WebApp2 Tutorial

Exercise 7.1. Creating additional Google App pages

• Lets create a new sub-page under your Google App engine application
  • NB! Make sure you DO NOT overwrite your current main page as this would remove your previous lab submission when you deploy your application later!
• Create a new python file under your Google app engine project folder named second.py
  • Inside the new python file, create a new class for displaying the page content
    • For example: class SecondMainPage(webapp2.RequestHandler):
    • Also add a get(self) method and display some text on the web page. get(self) method corresponds to HTTP GET request.
  • Import the webapp2 module: import webapp2
• In the original python file, import the classes from the newly created file:
  • from second import *
• In the original python file, Create a new entry under application = webapp2.WSGIApplication for the newly created page
  • It should link /secondexercise to SecondMainPage class
• Deploy the application and check that everything is working correctly and /secondexercise page is accessible.
• From now on, continue adding new content to the second.py file while only changing the original file to modify the application = webapp2.WSGIApplication entries.

Exercise 7.2. Using the Google NDB Datastore service

We will now implement a message board functionality for the /secondexercise page and you will learn how to store data (In our case it will be messages) in the Google Datastore. You should notice that you do not need to set up a database or database schemas, all you need to do is to use the Google ndb API and the PaaS takes care of everything else for you.

• Create a new NDB object class Message
  • Check https://cloud.google.com/appengine/docs/standard/python/ndb/creating-entity-models to see how it is done.
  • It must have the following fields
    • message_from - name of the sender, String type
    • message_text - message content, String type
    • message_time - time of the message, DateTime format
      • DateTime should have an option: auto_now=True
      • You can check the supported data types from here: https://cloud.google.com/appengine/docs/standard/python/ndb/entity-property-reference
• Create a new form for entering messages on the /secondexercise page
  • <form action="/message" name ="myform" method="post">
  • From: <input type="text" name="from" /> <br />
  • Message: <input type="text" name="text" />
  • <input type="submit" value="Submit" name="submit">
  • </form>
• Create a class HandleMessage for processing the message form and link it to sub-page /message
• Add a def post(self): method to HandleMessage class
  • post(self) method corresponds to HTTP POST request.
  • You can access the entered form data from inside the post method like this:
    • m_from = self.request.get('from')
  • Create a new Message object using the entered data and enter it to database:
    • message = Message(message_from=m_from, message_text=m_text)
    • message.put()
  • output a confirmation about the entered message and create a HTML link back to the http://<your_google_app_id>.appspot.com/secondexercise page

Exercise 7.3. Displaying data from NDB Datastore

We also need to display the messages which have been submitted by the users.

• Modify the /secondexercise page to display the latest 10 Messages from NDB
  • Check https://developers.google.com/appengine/docs/python/ndb/queries on how to query NDB.
  • Create a query for all data from Message's
  • Sort by Message.message_time in Descending order
  • Fetch 10 entries
  • create a cycle over all the results and print them out one at a time
    • Use cgi library to escape any unneeded html characters
      • import cgi
      • For example: self.response.out.write(cgi.escape(message.message_text))

Exercise 7.4. Add user identification and information to the Messages

Lets simplify creating messages by fetching the user name directly from the Google App Engine user service, like we did in the last lab.

• Use the Google user API for log in and authentication, just like in last week lab.
• Verify that user authentication is working. User should not be able to send or view messages if they have not logged in.
• Remove the "From" field from the message form and replace it with the username or full name from the google user service (user.nickname()).
• Display the name of the user in the list of posted messages.

Deliverables

• Deploy the latest version of the application in App Engine
  • NB! Verify that your previous lab assignment is also still working in appspot.com
• Provide the full web link to your GoogleAppEngine second exercise page
• Upload the source code of your full Google App.