Fat model & Skinny controller examples

post.rb

# /app/models/post.rb
class Post< ActiveRecord::Base
  def repost_by(repost)
    if self.user == retweeter
      "Sorry, you can't retpost your own posts"
    elsif 
      self.retposts.where(:user_id => repost.id).present? "You already reposted!"
    else
      # ...
      "Succesfully reposted"
    end 
  end
end