s.add_dependency 'friendly_id','~> 5.0.0'

在engine.gemspec文件中然后执行：@H_404_5@

bundle install #=> works
rails g friendly_id #=> works
rake db:migrate

我明白了：@H_404_5@

rake aborted!
uninitialized constant FriendlyId

嗯什么？@H_404_5@

更新 – 使用FriendlyId的模态@H_404_5@

module Xaaron
     class Role < ActiveRecord::Base
        extend FriendlyId
        friendly_id :role,use: :slugged

        validates :role,presence: true
        validates_uniqueness_of :role
      end
   end