I'm starting with RoR today, but I buy a RoR 3.2 book, and my installation on Ubuntu is Rails 4 and Ruby 2.0.
Anyway, in book I have this code:
But, not works in Rails 4.
2.0.0-p247 :074 > article.errors.on(:title) NoMethodError: undefined method `on' for #<ActiveModel::Errors:0x0000000427e238> from (irb):74 from /home/patrick/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands/console.rb:90:in `start' from /home/patrick/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands/console.rb:9:in `start' from /home/patrick/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands.rb:64:in `<top (required)>' from bin/rails:4:in `require' from bin/rails:4:in `<main>' 2.0.0-p247 :075 >
What is equivalent