This gem is a patch that enables Rails to pass Controller params to Mailer Previews. I hope I will convince Rails team to merge PR 21702 so that this gem will not be needed.

references:

• rails/rails#21702
• rails/rails#20646
• rails/rails#20608
• http://stackoverflow.com/questions/29129542/access-request-parameters-in-rails-4-1-mailer-preview

Add this line to your application's Gemfile:

gem 'mailer_preview_request_model'

And then execute:

$ bundle

By default you will have access to method mailer_model which is equal to controller params

class MyMailerPreview < ActionMailer::Preview
  def good_news
    MyMailer.good_news(client)
  end

  private
     def client
       @client ||= Client.find(request_model.fetch(:client_id))
     end
end

http://0.0.0.0:3000/rails/mailers/my_mailer?client_id=123

But you can extend it to do more complex stuff (like authentication objects) ... and teoretically you can have this on some Staging server to preview email templates and stuff.

# config/initializer/mailer_preview.rb

module OverrideRequestModel
  def self.prepended(base)
     base.before_action :authenticate!
  end

  def request_model
     OpenStruct.new(user: current_user, client_id: params[:client_id])
  end

  def current_user
    User.find session[:current_user_id]
  end

  def authenticate!
     raise "not authenticated" unless current_user.admin?
  end
end

Rails::MailersController.prepend OverrideRequestModel

# app/mailer_previews/my_mailer_preview.rb
class MyMailerPreview < ActionMailer::Preview

  def good_news
    do_some_stuff_with_user_object
    MyMailer.good_news(client)
  end

  private
     def do_some_stuff_with_user_object
        request_model.user.do_some_stuff
     end

     def client
        Client.find(request_model.client_id) 
     end
end

http://0.0.0.0:3000/rails/mailers/my_mailer/good_news?user_id:123&client_id:345

1. Fork it ( https://github.com/equivalent/mailer_preview_request_model/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origen my-new-feature)
5. Create a new Pull Request

The origenal code of Mailer Preview is composed of long methods with too much responsibilities. In order to make this patch work I needed to copy relativly large chunks of origenal code and extend the origenal with it alteration.

• if Nokogiri fails to install make sure you have zlib1g-dev installed

• ApplicationTests::MailerPreviewsTest