Delegate method

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I want to make a quick post about a new Rails method, delegate, that I came across recently. It's a really useful way to refactor code in order to cut down on the number of public object methods that you have to explicitly define. You can read the documentation for the delegate method here

Take this code for a QueueItem model

class QueueItem < ActiveRecord::Base
  belongs_to :user
  belongs_to :video

  def video_title
    video.title
  end

  def rating
    review = Review.where(user_id: user.id, video_id: video.id).first
    review.rating if review
  end

  def category_name
    video.category.name
  end

  def category
    video.category
  end
end

There are several simple methods here and this is where delegate comes in handy to tidy this up. By using delegate my code will look as follows:

class QueueItem < ActiveRecord::Base
  belongs_to :user
  belongs_to :video

  # This means I don't need a category method to return video.category.
  # When QueueItem.category is called it automatically looks for video.category
  # Also, for category_name I don't need video.category.name because video.category is already delegated as category
  delegate :category, to: :video

  # This means I do not need a video_title method to return video.title
  # When QueueItem.video_title is called it automatically looks for video.title
  delegate :title, to: :video, prefix: :video

  def rating
    review = Review.where(user_id: user.id, video_id: video.id).first
    review.rating if review
  end

  def category_name
    category.name
  end
end

I've commented the code to further explain how the delegate method works in this case. Now I have a much neater model!

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