如何在Active Admin:Rails中为管理员提供不同的访问级别？

# app/models/role.rb
class Role < ApplicationRecord
  has_many :users
  has_many :permissions, through: :role_permissions

  validates :name, presence: true, uniqueness: true
end

# app/models/permission.rb
class Permission < ApplicationRecord
  has_many :role_permissions
  has_many :roles, through: :role_permissions

  validates :name, presence: true, uniqueness: true
end

# app/models/role_permission.rb
class RolePermission < ApplicationRecord
  belongs_to :role
  belongs_to :permission
end

# app/models/user.rb
class User < ApplicationRecord
  has_many :user_roles
  has_many :roles, through: :user_roles

  def can?(action)
    roles.joins(:permissions).where(permissions: { action: action }).exists?
  end
end

# app/models/user_role.rb
class UserRole < ApplicationRecord
  belongs_to :user
  belongs_to :role
end

# app/admin/users.rb
ActiveAdmin.register User do
  controller do
    before_action :check_permissions

    private

    def check_permissions
      unless current_admin.can?('manage_users')
        redirect_to admin_root_path, alert: 'Access denied'
      end
    end
  end
end

# app/admin/menu.rb
module ActiveAdmin
  module Views
    module Pages
      class Base < Arbre::HTML::Document
        def build(page)
          super
          if current_admin.can?('view_dashboard')
            build_menu
          end
        end
      end
    end
  end
end