undefined method `authenticate_user! Api::PostsController in Devise / Rails 4 -

there following routes in project:

  root 'home#index'    namespace :api, defaults: { format: :json }     devise_for :users, controllers: { sessions: "api/sessions" }     resources :posts   end 

user model:

class user < activerecord::base     has_many :posts,        dependent: :destroy     has_many :comments, dependent: :destroy      validates :name, presence: true      devise :database_authenticatable, :rememberable end 

session controller:

class api::sessionscontroller < devise::sessionscontroller   def create     @user = user.find_for_database_authentication(email: params[:user][:email])     if @user && @user.valid_password?(params[:user][:password])         sign_in(@user)     else         warden.custom_failure!       @errors = [ 'invalid email or password' ]         render 'api/shared/errors', status: :unauthorized     end     end end 

application controller:

class applicationcontroller < actioncontroller::base   # prevent csrf attacks raising exception.   # apis, may want use :null_session instead.   #protect_from_forgery with: :exception end 

at last post controller:

class api::postscontroller < applicationcontroller     before_action :authenticate_user!, only: [ :create ]      def create       current_user.posts.create!(post_params)     end      private          def post_params             params.require(:post).permit(:title, :content)         end end 

but when try create new post following error: "undefined method `authenticate_user! api::postscontroller". if delete it, error 'current_user' method. what's trouble? how can fix it? in advance!!!

you error because of nesting devise within :api namespace in routes.rb file. therefore, should authenticate users in following way:

class api::postscontroller < applicationcontroller     before_action :authenticate_api_user!, only: [ :create ] end