rails - if condition on view - undefined method `id' for nil:NilClass - ruby-on-rails

Question

I have a class called #Subdomain:
Here is my controller:
class SubdomainsController < ApplicationController
before_action :authenticate_user!, only: [:edit, :update]
before_action :set_subdomain, only: [:show, :edit, :update, :destroy]
before_action :redirect_to_subdomain, only: :show
before_action :redirect_to_subdomain_show, only: :root, unless: '#subdomain.nil?'
def root
render nothing: true
end
def index
#subdomains = Subdomain.all
end
def show
end
def new
#subdomain = Subdomain.new
end
def edit
end
def create
#subdomain = Subdomain.new(subdomain_params)
respond_to do |format|
if #subdomain.save
format.html { redirect_to #subdomain, notice: 'Subdomain was successfully created.' }
format.json { render :show, status: :created, location: #subdomain }
else
format.html { render :new }
format.json { render json: #subdomain.errors, status: :unprocessable_entity }
end
end
end
def update
respond_to do |format|
if #subdomain.update(subdomain_params)
format.html { redirect_to #subdomain, notice: 'Subdomain was successfully updated.' }
format.json { render :show, status: :ok, location: #subdomain }
else
format.html { render :edit }
format.json { render json: #subdomain.errors, status: :unprocessable_entity }
end
end
end
def destroy
#subdomain.destroy
respond_to do |format|
format.html { redirect_to subdomains_url, notice: 'Subdomain was successfully destroyed.' }
format.json { head :no_content }
end
end
private
def redirect_to_subdomain_show
redirect_to subdomain_url(#subdomain) if #request_subdomain.eql? #subdomain.address
end
# Redirect to subdomain... if the current one isn't equal to #subdomain.address column
def redirect_to_subdomain
redirect_to subdomain_url(#subdomain, subdomain: #subdomain.address) unless #request_subdomain.eql? #subdomain.address
end
def set_subdomain
#subdomain = Subdomain.find(params[:id])
end
def subdomain_params
#subdomain.assign_attributes(tag_speciality: params[:subdomain][:tag_speciality].split(','))
params.require(:subdomain).permit(
:domain_id,
:address,
:title,
:description,
:is_published,
:button_text_client,
:button_text_service,
:cover,
:primary_colour,
:secundary_colour,
:contrast_colour,
:logo,
:find_clients,
:find_professional,
:start_relation,
:publications_wall,
:tag_speciality,
:cards_wall
)
end
end
On the view i created a condition:
<% if (!#subdomain.id.blank?) %>
<li>
<%= link_to cards_from_subdomain_path(subdomain_id: #subdomain.id) do %>
<i class="fa fa-search fa-lg"></i>
<span class="hidden-medium">
&nbsp <%= #subdomain.cards_wall %>
</span>
<% end %>
</li>
<li>
<%= link_to publications_from_subdomain_path(subdomain_id: #subdomain.id) do %>
<i class="icon-grid fa-lg"></i>
<span class="hidden-medium">
&nbsp <%= #subdomain.publications_wall %>
</span>
<% end %>
</li>
<% else %>
<li>Some thing</li>
<% end %>
Here is the model:
class Subdomain < ActiveRecord::Base
belongs_to :domain
has_many :cards
mount_uploader :cover, AssetsUploader
mount_uploader :logo, AssetsUploader
end
When the #subdomain exist is ok, everything works fine, but when it doesn't exist, i get this error message:
NoMethodError in Subdomains#index
undefined method `id' for nil:NilClass
<% if (!#subdomain.id.blank?) %>
What could i do to fix that? thanks

Answer 1

The quick and dirty solution would be to use #try (not recommended though)
<% if !#subdomain.try(:id).try(:blank?) %>
By the way, you can use #present? instead of negating a #blank? to make code more readable.
However, if I assume correctly and the #subdomain is an ActiveRecord model, you don't need to check if it's id is present. A following code should be sufficient in your case:
<% if #subdomain %>
(...)
<% else %>
(...)
<% end %>
If the #subdomain is not found, it will be a nil anyway - and then the if #subdomain condition will be evaluated as false - since nil is a falsy value.
And if you get this error because you happen to be rendering a collection like this:
= render 'subdomain', collection: #subdomains
...then you can just put that inside a condition...
<% if #subdomains.present? %>
= render 'subdomain', collection: #subdomains
<% else %>
<% # #subdomains are an empty collection %>
<% end %>

Answer 2

From your create action, id will definitely be created in your table. I don't still understand what you are trying to get to, for negating on #id.blank?.
Change the first line from your view. i.e.
<% if (!#subdomain.id.blank?) %>
to,
<% if #subdomains %>, which will definitely return all attributes on your Subdomain Table since its has being taken care of in your index action.
Another thing I do is wrap my if...else statement inside a loop, such the your view becomes:
<% #subdomains.each do |subd| %>
<% if subd.id.present? %> #you can use another attribute here instead of id. e.g. <% if subd.is_published == true %> since `is_published` is a boolean.
<li>
(#your codes here referenced with the format called `subd.whatever_attribute`)
</li>
<li>
(#your codes here referenced with the format called `subd.whatever_attribute`)
</li>
<% else %>
<li>Some thing</li>
<% end %>
<% end %>