未初始化的常量API :: V1 :: PopularSchoolsController-Rails API

在Rails应用中创建API时出现错误。错误是：

ActionController::RoutingError (uninitialized constant 
API::V1::PopularSchoolsController):

我的文件夹结构是：

我的路线：

namespace :api, defaults: {format: :json} do
    namespace :v1 do
      resources :popular_schools
    end
  end

控制器：

class API::V1::PopularSchool::PopularSchoolsController < ApplicationController

  def index
    @popular_schools = PopularSchool.all
    respond_to do |format|
      format.json { render json: @popular_schools }
    end
  end

end

inflections.rb：

ActiveSupport::Inflector.inflections(:en) do |inflect|
#   inflect.acronym 'RESTful'
    inflect.acronym 'API'
    inflect.acronym 'V1'
end