Ruby on Rails Access column from belongs_to table - ruby-on-rails-4

Question

I'm developing a CRUD and I have three tables clients, audit_cases and ra_cases.
The followings are the relationship of my models
class Client < ActiveRecord::Base
has_many :audit_cases
end
class AuditCase < ActiveRecord::Base
belongs_to :client
has_many :ra_cases
end
class RaCase < ActiveRecord::Base
belongs_to :audit_case
end
Model
def index
#a_cases = AuditCase.all
#b_cases = RaCase.all
end
I'm trying to join these three tables and show in a view
The following script works successfully
<tbody>
<% #b_cases.each do |b_case| %>
<tr>
<td><%= b_case.audit_case.client.Client_name %></td>
</tr>
<% end %>
</tbody>
But the following script have an error of undefined method `Client_name' for nil:NilClass
<tbody>
<% #a_cases.each do |a_case| %>
<tr>
<td><%= a_case.client.Client_name %></td>
</tr>
<% end %>
</tbody>
I can get the client array 'Client:0x007ff7d662adb0' if I use
<%= a_case.client %>
I'd like to know how could I modify my script if I want to extract parent's data from child(audit_cases) instead of from grandchild(ra_cases).
Thank you very much!

Answer 1

Due to some of the column "client.Client_name" are nil,
It works after I add this code "unless a_case.client.nil?"
<%= a_case.client.Client_name unless a_case.client.nil? %>

Answer 2

It doesn't look like each relation is required, so there may be some AuditCase records in your database that don't have Client records associated with them (or the Client record was destroyed). The consequence of that is that your view will raise an error because it tries to call a method on nil.
To get the view working, I would nil-guard it in some way. If you want to enforce a requirement around the client-case relationship, that's a different issue.
Here are some possible nil guard ideas:
# If you're using Ruby 2.3+, you can use the Safe Navigation Operator
<tbody>
<% #a_cases.each do |a_case| %>
<tr>
<td><%= a_case.client&.Client_name %></td>
</tr>
<% end %>
</tbody>
# Rails also provides a #try method
<tbody>
<% #a_cases.each do |a_case| %>
<tr>
<td><%= a_case.client.try(:Client_name) %></td>
</tr>
<% end %>
</tbody>
# or just a rough nil check
<tbody>
<% #a_cases.each do |a_case| %>
<tr>
<td><%= a_case.client.Client_name if a_case.client %></td>
</tr>
<% end %>
</tbody>
Let me know if that works.
From a ruby style perspective, I would avoid capitalizing methods like Client_name. Capitalization defines a constant/class in ruby.