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   [2]gnikyt Code ramblings.

                            Extending a Rails Engine

   /* Feb 20, 2016 — 4.3KB */

   Redesigning my CMS in Rails has been great fun. There have been many
   challenges faced, and many conquered (like having 100% code coverage
   :D). One thought that crossed my mind after building the monster was
   how do you extend an engine? By extending, I mean to add or overwrite
   methods of controllers, models, helpers, etc.

   The [3]Rails Engine Guide is excellent and it has two main points on
   extending the engine functionality. One is by use of “decorators” and
   the other is by abstracting all your controller and model code into
   concerns inside your engine. While I like the concern method, as it
   gives more flexibility for complex extensions, its overkill in my
   opinion. The [4]decorator option is very easy to implement without
   changing much of your existing engine.

   The first step as the Rails guide shows you, is to add support for
   decorator loading inside your engine lib. Below is how I did it in my
   CMS engine called Guts:

# lib/guts/engine.rb
# ... etc ...
isolate_namespace Guts

config.to_prepare do
  Dir.glob("#{Rails.root}app/decorators/*/guts/*_decorator*.rb").each do |c|
    require_dependency c
  end
end
# ... etc ...

   This will look for all decorators in the main Rails apps for the path
   app/decorators/{controllers,models,concerns,helpers,etc}/guts/{file}_de
   corator(s).rb and load them in using [5]require_dependency.

   Now the engine has support to load the decorators, lets move on to some
   examples. All following examples from here-on-out will be using my
   engine for example purposes.

Controllers

   Create a file in app/decorators/controllers/guts/ such as
   type_decorator.rb

   Add in the following code using class_eval from Ruby:

Guts::TypesController.class_eval do
  # Decorator action is explode.. we will route this as: guts/types#explode
  def explode
    # Will render app/views/guts/types/explode.html.erb
  end
end

   Next open app/config/routes.rb in your main Ruby app and prepend this
   new route at the very top of the route file before mounting the Guts
   engine in the Rails.application.routes.draw block.

   As an example:

Guts::Engine.routes.prepend do
  # Create a route of /guts/types/explode
  # Map it to types controller and the explode method
  # Give the route a name of guts_types_explode
  get "/types/explode", to: "types#explode", as: :guts_types_explode
end

Rails.application.routes.draw do
  # Mount the Guts engine
  mount Guts::Engine => "/guts"
end

   This will now prepend our new route to the engine and map
   /guts/types/explode to our decorator action.

   Lastly, create a view in app/views/guts/types/ called explode.html.erb
   with whatever you wish to display! This is the basics of extending a
   controller.

Models

   As in controllers, create a file in app/decorators/models/guts/ such as
   type_modal_decorator.rb

   Add in the following code using class_eval from Ruby:

Guts::Type.class_eval do
  # Override title setter
  def title=(title)
    self[:title] = "Tricked ya! New Title!"
  end

  # Adds a new method to the model
  def title_with_bang
    "#{self[:title]}!"
  end
end

Views

   As stated above for the controller example, since Rails looks in the
   main app for views first, you simply need to match the correct path.

   If your engine’s view for CoolController#jumps is
   app/views/{engine}/cool/jumps.html.erb you will duplicate this in your
   main Rails apps by creating a file in
   app/views/{engine}/cool/jumps.html.erb. You can then enter anything you
   need into that view and will be overridden.

   A good tip I used in my CMS engine was to utilize [6]yields. I placed
   named yields in many parts of my engine views so they can be utilized
   by a Rails app by calling [7]content_for in their views.

   Although the Rails Guide covers all this, I thought seeing a real-world
   example would help. Happy coding!

   [8]MD | [9]TXT | [10]CC-4.0

   This post is 9 years old and may contain outdated information.
     __________________________________________________________________

   [11]Ty King

Ty King

   A self-taught, seasoned, and versatile developer from Newfoundland.
   Crafting innovative solutions with care and expertise. See more
   [12]about me.
   [13]Github [14]LinkedIn [15]CV [16]RSS
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References

   Visible links:
   1. /rss.xml
   2. /
   3. http://edgeguides.rubyonrails.org/engines.html#improving-engine-functionality
   4. http://edgeguides.rubyonrails.org/engines.html#overriding-models-and-controllers
   5. http://apidock.com/rails/ActiveSupport/Dependencies/Loadable/require_dependency
   6. http://guides.rubyonrails.org/layouts_and_rendering.html#understanding-yield
   7. http://guides.rubyonrails.org/layouts_and_rendering.html#using-the-content-for-method
   8. /extending-a-rails-engine/index.md
   9. /extending-a-rails-engine/index.txt
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  15. /assets/files/cv.pdf
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