Database Listener for User Centric Events

Badgeyay is an open-source utility developed by FOSSASIA to generate badges for conferences and events. The project is separated into two components to ease maintainability. First is the frontend part which is in ember and second part is backend which is in Flask. The choice of database to support backend is PostgreSQL.

Now comes the problem, whenever a user is registered in the database, he should receive  a verification mail, that he is successfully registered on the platform. For this case we have to listen to the database events on User model. This issue has greater extendibility than only sending greeting or verification mail to the user. We can extend this to trigger services that are dependent on user registration, like subscribing the user to some set of services based on the plan he opted while registration and many more.

These type of issues cannot be handled by normal relationship with tables and other entities, there has to be logic in place to support such functionalities. So the challenges for tackling the problem are as follows:

  • Listen to the insert_action in User model
  • Extracting the details necessary for the logic
  • Execute particular logic


  1. Attaching insert_action listener to the User model. This function will get triggered whenever an entity is saved in the User model.

<!– HTML generated using –>

@db.event.listens_for(User, "after_insert")
def logic(mapper, connection, target): {
  1. When the function gets triggered, extract the details of the saved user that is necessary for the logic. As currently we are sending greeting mail to the user,we only need the email of the user. Target is the actual saved user passed as argument to the listening function from the library.

<!– HTML generated using –>

msg = {}
msg['subject'] = "Welcome to Badgeyay"
msg['receipent'] =
msg['body'] = "It's good to have you onboard with Badgeyay. Welcome to " \
"FOSSASIA Family."
  1. Now the details are passed to sendMail() function for sending mail which uses flask-mail library to send mail to the recipient.
    def sendMail(message):
    if message and message.receipent:
    msg = Message(
    sender=app.config['MAIL_USERNAME'], Response(200).generateMessage(
    except Exception as e:
    return jsonify(
    'Unable to send the mail'))
    return jsonify(
    'Mail Sent'))
    return jsonify(
    'No data received')) 'No data received'))
  2. This will send mail to the user who has been registered to the application.

Similarly we can use separate logics according to the need of the application.


The Pull Request for the above functionality is at this Link

Topics Involved

Working on the issue involve following topics:

  • Configuring mail service to allow insecure apps access.
  • Sending mail from the flask-mail to end user
  • Attaching listener to listen for database change
  • Extraction of data from saved object in database sqlalchemy.


  • Sending Mails Programmatically –  Link
  • Flask Mail Documentation – Link
  • Listening to database events – Link
  • Enabling access to GMAIL to send mails to recipient – Link