Rails Mailer

Rails includes a mailer facility. To use it, you need a model - a class that inherits from ActionMailer::Base - and the best way to do that is use Rails to generate it:

ruby script/generate mailer MyMailer send_book

This also creates some default views (in this case just one, send_book) and tests, but we will discuss that later. Let us suppose we want to send an e-mail with a record from a table called books. In a moment, we will set up a method called send_book in MyMailer, but first, let us look at how we will invoke the mailer. In books_controller, to send the mail, you need to invoke a class method that starts deliver_.

MyMailer.deliver_send_book(:user => current_user, :data => find_book)

Somewhere in ActionMailer::Base, there is a method_missing method that handles your request. It creates an instance of MyMailer, does some setting up that we do not have to worry about, then invokes the method send_book. This is where we assign values specific to this e-mail. It might look like this:

def send_book(options)
@recipients  = "#{options[:user].email}"
@from        = "book-database@mydomain.com"
@subject     = "Record from book database"
@sent_on     = Time.now
@content_type = 'text/html'
@body[:user] = options[:user]
@body[:book]  = options[:data]
end

Note that this will send the message in HTML format; it will default to plain text if there is no @content_type.

Next the method_missing method creates the text of the e-mail. It does this in the normal Rails manner, i.e., from a file in the views folder. In this case it will use views/my_mail/send_book.html.erb. When you create views/my_mail/send_book.erb, you have access to any variable you assign to the @body hash, so in the example above, I could use @user and @book, just as in a normal view. Similarly, you can use partials from other models/controllers in the normal way.

Finally ActionMailer sends the e-mail. It needs to know your your mail settings, which it will collect from a file mail.rb in config/initializers. This might look something like this:

# Email settings
ActionMailer::Base.delivery_method = :smtp
ActionMailer::Base.smtp_settings = {
  :address => "smtp.mydomain.com",
  :port => 25,
  :domain => "mydomain.com",
  :authentication => :login,
  :user_name => "rails",
  :password => "secret"
}

You can use your helper files in your mail views just like your normal views, just remember to declare them at the top of MyMailer:

helper :application

The one slight difference is that you cannot do helper :all. I imagine an oversight in Rails.

Attachments can be added easily:

  attachment "application/rtf" do |a|
  a.body = File.read 'some_file.rtf'
  a.filename = 'samples.rtf'
end

Testing
You can test your mailer. Rails will have generated a default unit test (no functional testing as there is no controller for a mailer).

require 'test_helper'

class MyMailerTest < ActionMailer::TestCase
tests MyMailer
def test_send_book
  @expected.subject = 'MyMailer#send_book'
  @expected.body    = read_fixture('send_book')
  @expected.date    = Time.now

  assert_equal @expected.encoded,
    MyMailer.create_send_book(@expected.date).encoded
end

end

NB: The generated unit test includes a statement tests MyMailer. This seems to just invoke write_inheritable_attribute, which appears to make a copy of the class variables in te superclass in the subclass.

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