Rails 4: use MySql y MongoDB juntos

Estoy tratando de hacer una aplicación en los rieles 4 usando MongoDB (mongoid) y MySQL juntos. Pero no puedo configurarlo.

Estoy siguiendo los pasos a continuación:

rails new myapp -d mysqlLuego agregó estas líneas a Gemfile:
gem "mongoid"
gem "bson_ext"bundle installrails g mongoid:config

El paso 4 falla. No puedo resolver el problema. Muestra el siguiente error.

/home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid/associations.rb:5:inrequire': /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid/associations/has_many.rb:79: syntax error, unexpected keyword_do_cond, expecting ':' @documents = attributes ? attributes.collect do |attrs| ^ /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid/associations/has_many.rb:84: syntax error, unexpected ':', expecting keyword_end end : [] ^ /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid/associations/has_many.rb:99: syntax error, unexpected keyword_do_cond, expecting keyword_end attributes.values.each do |attrs| ^ /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid/associations/has_many.rb:139: syntax error, unexpected keyword_end, expecting end-of-input (SyntaxError) from /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid/associations.rb:5:in'de /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid.rb:40:inrequire' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid.rb:40:in'de /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler/runtime.rb:76:inrequire' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler/runtime.rb:76:inbloque (2 niveles) en require 'from /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler/runtime.rb:72:ineach' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler/runtime.rb:72:inbloquear en require 'de /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler/runtime.rb:61:ineach' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler/runtime.rb:61:inrequire 'de /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler.rb:134:inrequire' from /home/devesh/fashion_hub/store/config/application.rb:7:in'de /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application.rb:82:inrequire' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application.rb:82:inpreload 'de /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application.rb:143:inserve' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application.rb:131:inbloque en ejecución 'desde /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application.rb:125:inloop' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application.rb:125:inejecutar 'desde /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application/boot.rb:18:in<top (required)>' from /home/devesh/.rvm/rubies/ruby-2.2.2/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:inrequire 'de /home/devesh/.rvm/rubies/ruby-2.2.2/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'

Estaba siguiendo estourl.

Algunos detalles:

SO - ubuntu 14.04Ruby v2.2.2rieles 4.2.3