Rails: second-level associations/undefined method error

Question

I have these methods:

class Item < ApplicationRecord
  has_many :fabrics
end

class Fabric < ApplicationRecord
  belongs_to :item
  has_many :inventories
end

class Inventory < ApplicationRecord
  belongs_to :fabric
end

Controller:

class InventoryController < ApplicationController

def index
  @inventory = Inventory.all
end

And view:

<% @inventory.each do |f| %>
    <tr>
        <td><%= f.fabric.item %></td>
    </tr>
<% end %>

I get this error:

ActionView::Template::Error (undefined method `item' for nil:NilClass):

Can someone explain why I am getting this error? Is it because of scopes? I've read Active Record Associations Guide ( http://guides.rubyonrails.org/association_basics.html#belongs-to-association-reference ). Under '4.1.3.2 includes' there is an example similar to my model associations which says this should be fine?

Answer 1

This error means that some of the inventories does not have related fabric, etc inventory.fabric == nil . You need to manage this case in the view code:

<% @inventory.each do |f| %>
    <tr>
        <td><%= f.fabric ? f.fabric.item : "Without item" %></td>
    </tr>
<% end %>