{ tags: [
    {  "id": 1,
       "name": Mens,
       "items": [
          {
             "id": 1,
             "name": shirts,
             "liking_users": [
                    {
                       "id": 1,
                       "name": Tom
                     },
                     {
                       "id": 2,
                       "name": Steve
                     }
              ]
           }
        ]
     }
   ]
}

class Tag < ActiveRecord::Base
  has_many :items
end

class Item < ActiveRecord::Base
   has_many :likes, dependent: :destroy
   has_many :liking_users, through: :likes, source: :user
end

class User < ActiveRecord::Base
   has_many :likes, dependent: :destroy
   has_many :like_items, through: :likes, source: :item
end

class Like < ActiveRecord::Base
   belongs_to :item
   belongs_to :user
end

module API
  module V1
    class Tags < Grape::API
      resource :tags do

  　　   desc 'GET /api/v1/tags/:id'
  　　　  params do
     　　　 requires :id, type: Integer, desc: "Tag id."
    　　　end
   　　　 get '/:id' do
    　  　　tag = Tag.find(params[:id])
     　　　 @tag = tag.items.  #この行をどう書けばいいかわからないです、、
    　　　end
      end
    end
  end
end