A simple URL shortened in Sinatra with Mongoid.

url_shortener.rb

require 'sinatra'
require 'mongoid'

configure do
   Mongoid.configure do |config|
    name = "url_shortener"
    host = "localhost"
    config.master = Mongo::Connection.new.db(name)
    config.persist_in_safe_mode = false
  end
end

class Url
	include Mongoid::Document
	field :url, :type => String
	field :ident, :type => String

  before_create :set_ident
  validates_presence_of :url
  validates_format_of :url, :with => URI::regexp(%w(http https)), :message => "not valid URL"
  validates_uniqueness_of :url, message: "already taken"

  private
	# Generate a unique identifier for the URL.
  def set_ident
    loop do
      ident = ActiveSupport::SecureRandom.urlsafe_base64(5)
      if self.class.where(ident: ident).count == 0 # Loop until it's unique.
        self.ident = ident
        break
      end
    end
  end
end

get '/' do
	"POST URL to make new, GET an ident to redirect"
end

post '/' do
	url = Url.find_or_create_by(url: params["url"])
	if url.errors.empty?
		url.ident
	else
		url.errors.to_json
	end
end

get '/:ident' do |ident|
	url = Url.where(ident: ident).last
	if url
		redirect url.url, "Go to #{url.url}\n"
	else
		404
	end
end

get '/:ident.json' do |ident|
	url = Url.where(ident: ident).last
	if url
		url.to_json
	else
		404
	end
end

error 404 do
	"Not found"
end