Reminder notifications with delayed jobs and Twillio

Delayed jobs is a well-known way to integrate background processes in rails. The idea is to add some tasks or method calls to a queue. Then pass a datetime to the run_at method, so the background process can be executed at a selected time.

The plain and simple integration of delayed job is pretty straight forward. It does get a little more complicated when you need to add custom attributes to the different jobs. It could be if you wanted to execute the job at a certain time, depending on a timestamp in a record in the database. An example could be a reminder. You want to send a reminder to the user 2 hours before the event starts. You are able to do this by adding the run_at time on creation of the job. But what are we going to do if the event is update and the timestamp is changed? We need to be able to find the job in the jobqueue and update it accordingly. One way to do this could be adding polymorphic association to the delayed jobs.

Best explained with an example;

In this example I am using an event model and the Twilio service for text messages.

First off we need to add the delayed_jobs gem to our rails app. I'm using active record orm in this example, so we ill go with that - delayed_job_active_record

Gemfile

gem 'delayed_job_active_record', '~> 4.1', '>= 4.1.4' 

and run the generator:

rails generate delayed_job:active_record

This will give you the following migration:

class CreateDelayedJobs < ActiveRecord::Migration[5.2] def self.up   create_table :delayed_jobs, force: true do |table|     table.integer :priority, default: 0, null: false # Allows some jobs to jump to the front of the queue     table.integer :attempts, default: 0, null: false # Provides for retries, but still fail eventually.     table.text :handler,                 null: false # YAML-encoded string of the object that will do work     table.text :last_error                           # reason for last failure (See Note below)     table.datetime :run_at                           # When to run. Could be Time.zone.now for immediately, or sometime in the future.     table.datetime :locked_at                        # Set when a client is working on this object     table.datetime :failed_at                        # Set when all retries have failed (actually, by default, the record is deleted instead)     table.string :locked_by                          # Who is working on this object (if locked)     table.string :queue                              # The name of the queue this job is in     table.timestamps null: true   end    add_index :delayed_jobs, [:priority, :run_at], name: "delayed_jobs_priority" end  def self.down   drop_table :delayed_jobs endend 

For now we will not add any extra columns to this migration, because I want to show the simple solution first, without the polymorphic association.

Lets start out with the simple implementation;

The generator created the migration above, so remember to do the

rails db:migrate

So now we need to make the method that will create the job. Let's call it reminder. In the events model, we can add this callback.

after_save :reminder

and then the reminder method.

 def reminder   # Send a text message reminder 2 hours before event start   @client = Twilio::REST::Client.new(Rails.application.credentials.twilio_account_sid, Rails.application.credentials.twilio_auth_token)             @client.messages.create({     from: "Name",     to: "phone number",     body: "Message to the user"     }) end

What happens now is that after a new event is created, the reminder method will run. The reminder method contains dummy code, but the fields should be populated with relevant data..

Now to the important part, right now this text will be sent as soon as the event is created. delayed_jobs gives us this method that we can add after the method:

handle_asynchronously :reminder, :run_at => Proc.new { |i| i.when_to_run }

This handles the reminder method asynchronously and a proc is created to determine the value of the parameter. I created a when_to_run method which is passed to the proc, where a value is returned based on the events starts_at value.

def when_to_run   minutes_before_appointment = 120.minutes   self.event.starts_at - minutes_before_appointment end

And that is actually it. The reminder method is now run 2 hours before the starts_at for the event and a text message is sent.

The issue we face now is if the events starts_at datetime is changed, then we have no way of finding the job and update the value. To solve this issue, we will have to add a few more columns to the delayed_jobs table.

Extended implementation

Now that we understands the basic implementation we can consider if we need the option to update the delayed_jobs or not. If so, we will have to add extra columns to the delayed_jobs table.

I suggest using polymorphic association, in order to provide the option to filter the different types of delayed_jobs. We will also be able to find and update specific jobs.

So lets start out with the migration:

rails generate migration add_delayable_to_delayed_jobs delayable:references{polymorphic}

A new migration is created

class AddDelayableAssociationToDelayedJobs < ActiveRecord::Migration[5.2] def change   add_reference :delayed_jobs, :delayable, polymorphic: true endend

run the migration

rails db:migrate

We now have the option to populate the 2 fields that references the type and id of a record. Since the delayed_jobs.rb is a headless model, we will have to add a delayed_job.rb file to our initializers.

touch config/initializers/delayed_job.rb

While we are at it, create a new folder called jobs under the app dir.

mkdir app/jobs

This is where we will store the different jobs.

Open up the delayed_job.rb file and add the following:

class Delayed::Job < ActiveRecord::Base belongs_to :delayable, :polymorphic => trueend

Lets start by creating a reminder job in the jobs folder.

touch app/jobs/reminder_job.rb

Inside this file we have a few have to define a few methods:

ReminderJob = Struct.new(:event) do  def enqueue(job)   job.delayable = event   job.save! end  def perform   event.send_reminder end  def queue_name   'reminder_queue' endend 

We are creating a new Struct, where we take event as an argument. The event has a starts_at datetime that we will use to determine when to send the reminder. The enqueue method queues the job and the perform method executes the job. This will get clearer in a moment. I also added a queue_name for scalability, it is good practice to have more than 1 queue if you plan on extending this feature with other delayed jobs.

Let's revisit our reminder method. Open up the model file and add a method called new_reminder and also rename the callback to new_reminder.

after_save :new_reminder  def new_reminder   Delayed::Job.enqueue(ReminderJob.new(self), { run_at: self.when_to_run }) end  def send_reminder   # Send a text message reminder 2 hours before event start   @client = Twilio::REST::Client.new(Rails.application.credentials.twilio_account_sid, Rails.application.credentials.twilio_auth_token)             @client.messages.create({     from: "Name",     to: "phone number",     body: "Message to the user"     }) end  def when_to_run   minutes_before_appointment = 120.minutes   self.starts_at - minutes_before_appointment end

What is happening now is that upon create, we use the after_save callback to run the new_reminder method. This method will queue up a delayed_job where it creates a new ReminderJob. The run_at is again populated with the value from the when_to_run method.

The new reminder job queues the job with the association to the event and then runs the perform method at the selected time, which comes from the run_at method.

And that's it.

A few things to keep in mind. If an event is updated, you will have to fetch the job and update it with a new run_at value. You can do this, since each job will contain the id and type as references.

An option would be to add a after_update callback, where you check if the starts_at is changed. If it is, then update the run_at value for the delayed job and save it.

def update_reminder  if.self.starts_at_changed?    job = Delayed::Job.find_by(delayable_id: event.id)    job.run_at = @event.starts_at - 2.hours    job.save  endend