我在练习 Ruby on Rails Tutorial 第 6 章，控制台手动创建新用户的时候，报这个错误，求高手指点一下：

NoMethodError: undefined method cost' for BCrypt::Engine:Class from D:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activemodel-4. 0.2/lib/active_model/secure_password.rb:104:inpassword=' from D:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4 .0.2/lib/active_record/attribute_assignment.rb:42:in public_send' from D:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4 .0.2/lib/active_record/attribute_assignment.rb:42:in_assign_attribute'

PS: 我用的 bcrypt-ruby 是 3.1.2 版本，不是教程里的 3.0.1 版本，因为在 Gem 里使用 3.0.1 版本时，会报冲突：

You don't have bcrypt-ruby installed in your application. Please add it to your Gemfile and run bundle install Gem::LoadError: can't activate bcrypt-ruby (~> 3.1.2), already activated bcrypt- ruby-3.0.1-x86-mingw32. Make sure all dependencies are added to Gemfile. from D:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/bundler-1.3.5/ lib/bundler/rubygems_integration.rb:224:in `block in replace_gem'

可能是我装的 railsinstaller 自带的 bcrypt-ruby 版本时 3.1.2....

已解决： 1 把 secure_password.rb 里的 gem 'bcrypt-ruby', '~> 3.0.0' 改成 gem 'bcrypt-ruby', '~> 3.1.0'1 2 项目文件夹里 Gemfile 里用 gem 'bcrypt-ruby', '3.1.2'。