http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CFsQFjAC&url=http://vmg.pp.ua/books/%25D0%259A%25D0%25BE%25D0%25BF%25D1%258C%25D1%258E%25D1%2582%25D0%25B5%25D1%2580%25D1%258B%25D0%2598%25D1%2581%25D0%25B5%25D1%2582%25D0%25B8/ruby/Rails%2520Recipes%2520-%2520Rails%25203%2520Edition(2012).pdf&ei=rbvFT6-8KebU2AXDv_zEAQ&usg=AFQjCNFDhcgnlXzTOx7NVqLqYN910zXCyA&sig2=dsSy6t0Q59BNaJ0LOm1eEA