undefined method `has_role?' for nil:NilClass - ruby-on-rails

Question

Trying to apply a rolify method to my user, I get the following error:
undefined method `has_role?' for nil:NilClass
I don't understand why, because current_user should be a global method accessible in every view right? How can it be nil?
Thanks!
Controller
def show
#photo = Photo.friendly.find(params[:id])
impressionist(#photo)
#photos = Photo.latest_photos
#user = #photo.user
#pin = Pin.new
#pin.photo_id = #photo.id
#category = Category.all
#commentable = #photo
#comments = #commentable.comments
#comment = Comment.new
#sponsors = #photo.sponsors
#zone = Zone.all
respond_to do |format|
format.html #show.html.erb
format.json {render json: #photo}
end
end
My view
<% if current_user.has_role? :admin %>
<%= link_to "Eliminar", user_photo_pin_path(user_id: #user.id, photo_id: #photo.id, id: pin.id) , method: :delete, data: { confirm: 'Quieres borrar esto?'}, class: "delete right" %>
<%= link_to 'Editar', edit_user_photo_pin_path(user_id: #user.id, photo_id: #photo.id, id: pin.id), :class=> "link", class: "edit quarter_margin_right right" %>
<% end %>
<% end %>

Answer 1

You need to check if there is a current_user in your views:
<% if current_user && current_user.has_role?(:admin) %>
<%= link_to "Eliminar", user_photo_pin_path(user_id: #user.id, photo_id: #photo.id, id: pin.id) , method: :delete, data: { confirm: 'Quieres borrar esto?'}, class: "delete right" %>
<%= link_to 'Editar', edit_user_photo_pin_path(user_id: #user.id, photo_id: #photo.id, id: pin.id), :class=> "link", class: "edit quarter_margin_right right" %>
<% end %>
<% end %>
This uses boolean short-circuiting - if current_user is nil then current_user.has_role? :admin is never evaluated.
If you are using Devise you can also use the user_signed_in? helper method.
Added.
If you find a yourself doing this often you can create a helper method:
# app/helpers/roles_helper.rb
module RolesHelper
def has_role?(role)
current_user && current_user.has_role?(role)
end
end
You can then simplefy your view:
<% if has_role?(:admin) %>
<%= link_to "Eliminar", user_photo_pin_path(user_id: #user.id, photo_id: #photo.id, id: pin.id) , method: :delete, data: { confirm: 'Quieres borrar esto?'}, class: "delete right" %>
<%= link_to 'Editar', edit_user_photo_pin_path(user_id: #user.id, photo_id: #photo.id, id: pin.id), :class=> "link", class: "edit quarter_margin_right right" %>
<% end %>
Note that we are calling has_role? on the view context.

Answer 2

For Devise to authenticate and set the current_user, you can include the following before_action in your controller:
before_action :authenticate_user!
If you only want to authenticate user for a specific action:
before_action :authenticate_user!, only: [:new, :update]
If you want to authenticate the user for all your controllers you can just put it in your ApplicationController