AutoPreviews

I got tired of writing ActionMailer::Preview classes. So I let Ruby write it for me.

In your mailer class, define some options:

class PostMailer < ApplicationMailer
  previews_for model: 'Post', # otherwise automatically infered based on class.name.delete_suffix('Mailer')
               params: { post_id: :id },
               only: [:created]

  previews_for model: 'Post',
               params: { post_id: :id },
               only: [:deleted],
               scope: :with_deleted,
               using: :arguments

  before_action only: [:created] do
    @post = Post.find_by(id: params[:post_id])
  end

  def created
    mail(to: "joshmn@example.com", subject: "Nice post #{@post.id}")
  end

  def deleted(post_id)
    @post = Post.find_by(id: post_id)
    mail(to: "joshmn@example.com", subject: "Deleted post #{@post.id}")
  end
end

In your previewer class, just call auto_preview!

class PostMailerPreview < ActionMailer::Preview 
  auto_preview! 
end 

auto_preview! will do some metaprogramming to create your mailer previews, like so:

  post = Post.first 
  params_to_send_to_mailer = {}
  params_given = { post_id: :id }
  params_given.each do |mailer_key, model_method| 
    params_to_send_to_mailer[mailer_key] = post.public_send(model_method) 
  end   
  PostMailer.with(params_to_send_to_mailer).created # or `*params_to_send_to_mailer.values` if `using: :arguments`

1. Add this line to your application's Gemfile:

gem 'auto_previews'

2. And then execute:

$ bundle

3. Restart your Rails server

4. Implement

5. Enjoy!

By default, the previews_for will define mailer preview methods for class.instance_methods(false).

• model: the model you want to use for the record lookup; defaults to self.class.name.delete_suffix('Mailer'); if false is passed, no model will be used
• params: a hash of mailer_method_name: :model_method_name; used to map values to the mailer from the model
• using: the type of mailer to use; defaults to using ActionMailer::Parameterized
• only: the methods to only use the given previews_for on; defaults to []
• except: the methods to not use the given previews_for on; defaults to []
• scope: scope to use on the model; defaults to :all

Just pass model: false and define some sort of values to pass in the params:

Passing a proc will call; passing a symbol will call the given method on the mailer preview class if it is defined, otherwise it will be sent to your mailer preview as the symbol.

class OneOffMailer < ApplicationMailer 
  previews_for model: false,
               params: {
                 subject: "Hi",
                 body: -> { FFaker::CheesyLingo.paragraph },
               }
end 

• More options
• Better extensibility
• Better record lookup
• Better serialization of mailer params

The gem is available as open source under the terms of the MIT License.