Fat model & Skinny controller examples

posts_controller(1).rb

# /app/controllers/posts_controller.rb
class PostController < ApplicationController
  def repost
    post = Post.find(params[:id])
    if post.user == current_user
      flash[:notice] = "Sorry, you can't repost your own posts"
    elsif post.reposts.where(:user_id => current_user.id).present? 
      flash[:notice] = "You already reposted!"
    else
      # ...
      flash[:notice] = "Succesfully reposted"
    end
    redirect_to post
  end
end