Best way to display something based on if user logged in or not

Question

I have an if statement that displays certain link based if a user voted or not for something. However, I'll get an error if the user is not logged in since current_user will be nil. I'm using devise for authentication.

undefined method `voted_as_when_voted_for' for nil:NilClass

               <% if current_user.voted_as_when_voted_for @pin %>                                                                                                                                                
                  <%= link_to dislike_pin_path(@pin), method: :put, class: "btn btn-default" do %>                                                                                                                
                      <span class="glyphicon glyphicon-heart"></span>                                                                                                                                                                   <%= @pin.get_upvotes.size %>                                                                                                                                                                
                  <% end %>                                                                                                                                                                                       
                <% else %>                                                                                                                                                                                        
                  <%= link_to like_pin_path(@pin), method: :put, class: "btn btn-default" do %>                                                                                                                   
                      <span class="glyphicon glyphicon-heart"></span>                                                                                                                                             
                      <%= @pin.get_upvotes.size %>                                                                                                                                                                
                  <% end %>                                                                                                                                                                                       
                <% end %>                                                                                                                                                                                         
                <%= link_to pins_path, class: "btn btn-default" do %>                                                                                                                                             
                    <span class="glyphicon glyphicon-step-backward"></span>                                                                                                                                       
                    Back                                                                                                                                                                                          
                <% end %>                                                                                                                                                                                         
                <% if user_signed_in? %>                                                                                                                                                                          
                  <%= link_to "Edit", edit_pin_path, class: "btn btn-default" %>                                                                                                                                  
                  <%= link_to "Delete", pin_path, method: :delete, data: { confirm: "Are you sure"}, class: "btn btn-default" %>                                                                                  
                <% end %>           

What can I add to that if statement to display one of the links even if the user is not logged in without repeating link_to code. Using DRY Rails methodology. (if a user is not logged in and clicks like/dislike link, it will ask him to log in since I have my routes set up like this:

before_action :authenticate_user!, except: [:index, :show] 

Answer 1

In your case:

<% if signed_in? && current_user.voted_as_when_voted_for @pin %>
  ...
<% end %>

Assuming you're using devise since you included the authenticate_user! method.

Answer 2

Try this:

<% if current_user && current_user.voted_as_when_voted_for @pin %>
   ... code here
<% else %> 
  <%= link_to like_pin_path(@pin), method: :put, class: "btn btn-default" do %>                                                                                                                   
    <span class="glyphicon glyphicon-heart"></span>                                                                                                                                             
    <%= @pin.get_upvotes.size %>                                                                                                                                                                
  <% end %> 
<% end %>