Automatically emailing a user when they create a post - ruby-on-rails

Question

I am a trainee full stack developer learning ruby on rails and am in month 1 of a 6 month intensive course.
I am working on a 'reddit' style app where users can create topics, posts and comments.
I am trying to automatically email a user when they create a new post.
I am using ActionMailer for this.
I am working on an after_create callback in my post model and a method in a mailer called 'favorite_mailer'.
The problem I am facing, is that I am unable to successfully implement an after_create callback, which triggers an email to be automatically sent to a user after they create a post.
I have defined a method in my mailer called new_post, which should receive 2 arguments (user, post).
I have defined a callback method in my Post model called send_new_post email but can't make it pass my Rspec tests.
Any help will be greatly appreciated.
I have created the following Post model spec:
describe "send_new_post_email" do
it "triggers an after_create callback called send_new_post_email" do
expect(post).to receive(:send_new_post_email).at_least(:once)
post.send(:send_new_post_email)
end
it "sends an email to users when they create a new post" do
expect(FavoriteMailer).to receive(:new_post).with(user, post).and_return(double(deliver_now: true))
post.save
end
end
Here is my Post Model (the relevant bit being the send_new_post_email callback):
class Post < ActiveRecord::Base
belongs_to :topic
belongs_to :user
has_many :comments, dependent: :destroy
has_many :votes, dependent: :destroy
has_many :favorites, dependent: :destroy
has_many :labelings, as: :labelable
has_many :labels, through: :labelings
after_create :create_vote
after_create :create_favorite
after_create :send_new_post_email
default_scope { order('rank DESC') }
validates :title, length: { minimum: 5 }, presence: true
validates :body, length: { minimum: 20 }, presence: true
validates :topic, presence: true
validates :user, presence: true
def up_votes
votes.where(value: 1).count
end
def down_votes
votes.where(value: -1).count
end
def points
votes.sum(:value)
end
def update_rank
age_in_days = (created_at - Time.new(1970,1,1)) / 1.day.seconds
new_rank = points + age_in_days
update_attribute(:rank, new_rank)
end
private
def create_vote
user.votes.create(value: 1, post: self)
end
def create_favorite
user.favorites.create(post: self)
end
def send_new_post_email
FavoriteMailer.new_post(self.user, self)
end
end
Finally, here is my mailer:
class FavoriteMailer < ApplicationMailer
default from: "charlietarr1#gmail.com"
def new_comment(user, post, comment)
# #18
headers["Message-ID"] = "<comments/#{comment.id}#your-app-name.example>"
headers["In-Reply-To"] = "<post/#{post.id}#your-app-name.example>"
headers["References"] = "<post/#{post.id}#your-app-name.example>"
#user = user
#post = post
#comment = comment
# #19
mail(to: user.email, subject: "New comment on #{post.title}")
end
def new_post(user, post)
# #18
headers["Message-ID"] = "<post/#{post.id}#your-app-name.example>"
headers["In-Reply-To"] = "<post/#{post.id}#your-app-name.example>"
headers["References"] = "<post/#{post.id}#your-app-name.example>"
#user = user
#post = post
# #19
mail(to: user.email, subject: "You have favorited #{post.title}")
end
end

Answer 1

I would not use a model callback to handle these kind of lifecycle events.
Why?
Because it is going to be called whenever you create a record which means you will have to override it in your tests.
ActiveRecord models can easily become godlike and bloated and notifying users is a bit beyond the models job of maintaining data and business logic.
It will also get in the way of delegating the notifications to a background job, which is very important if you need to send multiple emails.
So what then?
Well, we could stuff it in the controller. But that might not be optimal since controllers are PITA to test and we like 'em skinny.
So let's create an object with the single task of notifying the user:
module PostCreationNotifier
def self.call(post)
FavoriteMailer.new_post(post.user, post)
end
end
And then we add it to the controller action:
def create
#post = Post.new(post_params)
if #post.save
redirect_to #post
PostCreationNotifier.call(#post)
else
render :new
end
end
But - this probably is not what you want! Doh! It will only notify the creator that she just created a post - and she already knows that!
If we want to notify all the participants of a response we probably need to look at the thread and send an email to all of the participants:
module PostCreationNotifier
def self.call(post)
post.thread.followers.map do |f|
FavoriteMailer.new_post(f, post)
end
end
end
describe PostCreationNotifier do
let(:followers) { 2.times.map { create(:user) } }
let(:post){ create(:post, thread: create(:thread, followers: followers)) }
let(:mails) { PostCreationNotifier.call(post) }
it "sends an email to each of the followers" do
expect(mails.first.to).to eq followers.first.email
expect(mails.last.to).to eq followers.last.email
end
end
The pattern is called service objects. Having a simple object which takes care of a single task is easy to test and will make it easier to implement sending the emails in a background job. I'll leave that part to you.
Further reading:
http://www.sitepoint.com/comparing-background-processing-libraries-sidekiq/
https://blog.engineyard.com/2014/keeping-your-rails-controllers-dry-with-services