BP-FatModelSkinnyController.rb

# A user has many tweets.. and sometimes we want to retweet.

class TweetsController < ApplicationController

  def retweet
    @tweet = Tweet.find(params[:id])
    
    if @tweet.user == current_user
      flash[:notice] = "Sorry, you can't retweet your own tweets"
    elsif @tweet.retweets.where(:user_id => current_user.id).present?
      flash[:notice] = "You already retweeted!"
    else
      t = Tweet.new
      t.status = "RT #{@tweet.user.name}: #{@tweet.status}"
      t.original_tweet = @tweet
      t.user = current_user
      t.save
      flash[:notice] = "Succesfully retweeted"
    end
    
    render :show
  end
end

#  This is a good example where the logic belongs in a Model.  So our controller turns into 

class TweetsController < ApplicationController

  def retweet
    @tweet = Tweet.find(params[:id])
    
    result_message = @tweet.retweet_by(current_user)
    redirect_to(@tweet, :notice => result_message)
  end
end

# And the logic moves to the Model.

class Tweet < ActiveRecord::Base
  def retweet_by(current_user)
    if self.user == current_user
      "Sorry, you can't retweet your own tweets"
    elsif self.retweets.where(:user_id => current_user.id).present?
      "You already retweeted!"
    else
      t = Tweet.new
      t.status = "RT #{self.user.name}: #{self.status}"
      t.original_tweet = self
      t.user = current_user
      t.save
      "Succesfully retweeted"
    end
  end
end