Rails engine (api only) - undefined method `mount_devise_token_auth_for' for #<ActionDispatch::Routing::Mapper:

[adonespitogo]

I have a problem with running a rails engine in the host application. My integration tests pass but when I mount it in the host application, can't start the server due to the above error. Any idea?

Here's my routes:

Rails.application.routes.draw do

  root to: 'web_base#index'

  # ng2 html5 pushState routes
  get 'app', to: 'web_base#app'
  get 'app/*ngroute', to: 'web_base#app'

  mount_devise_token_auth_for 'User', at: 'auth'

  namespace :api, defaults: { format: :json } do


    resource :user
    resources :boards do
      resources :posts do
        resources :comments, only: [:index, :create, :update, :destroy]
      end
    end

    post '/api/share/board/', to: 'share_board#index', as: 'share_board'
    get  '/api/users/search', to: 'users#search', as: 'user_search'


  end

end

My gemspec

  s.add_dependency "rails", "~> 5.0.0", ">= 5.0.0.1"
  s.add_dependency "active_model_serializers"
  s.add_dependency "rack-cors"
  s.add_dependency "kaminari"
  s.add_dependency "api-pagination"
  s.add_dependency "devise_token_auth"
  s.add_dependency "omniauth"

Gemfile

source 'https://rubygems.org'
gemspec
gem "rails", "~> 5.0.0", ">= 5.0.0.1"
gem "active_model_serializers"
gem "rack-cors"
gem "kaminari"
gem "api-pagination"
gem 'devise_token_auth'
gem 'omniauth'

Error log:

[adones@Omars-imac-2 test_unsakini]$ rails s
=> Booting Puma
=> Rails 5.0.0.1 application starting in development on http://localhost:3000
=> Run `rails server -h` for more startup options
Exiting
/home/adones/Projects/UNSAKINI/unsakini/config/routes.rb:9:in `block in <top (required)>': undefined method `mount_devise_token_auth_for' for #<ActionDispatch::Routing::Mapper:0x00564862b63568> (NoMethodError)

[etagwerker]

@adonespitogo Did you try requiring the gem in routes.rb with something like require 'devise_token_auth'?

[zachfeldman]

Possible workaround posted by @etagwerker (thanks!) Closing for now.

[masroorhussainv]

@etagwerker, thanks. your solution works.

[udit99]

👋 Faced the same issue and the fix worked. Just wondering, is this something that should be in the docs, or better yet, in the generator? Or is it more complicated than that?