Where to put ruby helpers Sendgrid V3 Send API - ruby-on-rails

Question

I am trying to integrate Sendgrid using their Github documentation.
In their examples they suggest that you create a Mail Helper class but give very little guidance on how to actually do this.
I have a scheduled Rake task running using Heroku Scheduler that I would like to send an email when the task is complete and was hoping to use Sendgrid for this.
Currently I have the following code in /lib/tasks/scheduler.rake
require 'sendgrid-ruby'
include SendGrid
desc "Testing Email Rake"
task :test_sendgrid => :environment do
puts 'Starting Sendgrid Email Test'
send_task_complete_email()
puts 'Sendgrid Email Test Complete'
end
def send_task_complete_email
from = Email.new(email: 'test#example.com')
to = Email.new(email: 'test#example.com')
subject = 'Sending with SendGrid is Fun'
content = Content.new(type: 'text/plain', value: 'and easy to do anywhere, even with Ruby')
mail = Mail.new(from, subject, to, content)
sg = SendGrid::API.new(api_key: ENV['SENDGRID_API_KEY'])
response = sg.client.mail._('send').post(request_body: mail.to_json)
puts response.status_code
puts response.body
puts response.headers
end
I don't have the helper classes added anywhere as I am not sure which bits to add or where to put them. At the moment when I run this task I receive a 400 Bad request error back from Sendgrid and I believe it's because I don't have these helpers in place.
Any advice to fix this would be much appreciated as when I try to integrate without using the helpers and instead writing out the JSON I can successfully send the email but receive a TypeError: Mail is not a module when I try to deploy to Heroku.
UPDATE: ERROR RECEIVED USING ANSWER BELOW
400
{"errors":[{"message":"Invalid type. Expected: object, given: string.","field":"(root)","help":"http://sendgrid.com/docs/API_Reference/Web_API_v3/Mail/errors.html#-Request-Body-Parameters"}]}
{"server"=>["nginx"], "date"=>["Thu, 07 Jun 2018 09:02:42 GMT"], "content-type"=>["application/json"], "content-length"=>["191"], "connection"=>["close"], "access-control-allow-origin"=>["https://sendgrid.api-docs.io"], "access-control-allow-methods"=>["POST"], "access-control-allow-headers"=>["Authorization, Content-Type, On-behalf-of, x-sg-elas-acl"], "access-control-max-age"=>["600"], "x-no-cors-reason"=>["https://sendgrid.com/docs/Classroom/Basics/API/cors.html"]}

Answer 1

You need to use Action Mailer:
First create a mailer class to add your mail details (i.e. UserMailer):
$ bin/rails generate mailer UserMailer
it will create the following files:
create app/mailers/user_mailer.rb
create app/mailers/application_mailer.rb
invoke erb
create app/views/user_mailer
create app/views/layouts/mailer.text.erb
create app/views/layouts/mailer.html.erb
invoke test_unit
create test/mailers/user_mailer_test.rb
create test/mailers/previews/user_mailer_preview.rb
Now edit the file app/mailers/user_mailer.rb:
require 'sendgrid-ruby'
include SendGrid
class UserMailer < ApplicationMailer
def send_task_complete_email
from = Email.new(email: 'test#example.com')
to = Email.new(email: 'test#example.com')
subject = 'Sending with SendGrid is Fun'
content = Content.new(type: 'text/plain', value: 'and easy to do anywhere, even with Ruby')
mail = Mail.new(from, subject, to, content)
sg = SendGrid::API.new(api_key: ENV['SENDGRID_API_KEY'])
response = sg.client.mail._('send').post(request_body: mail.to_json)
puts response.status_code
puts response.body
puts response.headers
end
end
Then you can simply send emails using this code:
UserMailer.send_task_complete_email.deliver_now
Or from rake task:
desc "Testing Email Rake"
task :test_sendgrid => :environment do
puts 'Starting Sendgrid Email Test'
UserMailer.send_task_complete_email.deliver_now
puts 'Sendgrid Email Test Complete'
end
Update:
Because there is Mail module in Rails, you need to specify the correct SendGrid Mail module by changing:
mail = Mail.new(from, subject, to, content)
to
mail = SendGrid::Mail.new(from, subject, to, content)