#### TABLES ####
=# \d orders
                                         Table "orders"
   Column   |            Type             |                         Modifiers
------------+-----------------------------+-----------------------------------------------------------
 id         | integer                     | not null default nextval('orders_id_seq'::regclass)
 approved   | integer                     |
 removed    | integer                     |
 created_at | timestamp without time zone |
 updated_at | timestamp without time zone |
Indexes:
    "orders_pkey" PRIMARY KEY, btree (id)

=# select id,approved from orders limit 3;
 id | approved
----+----------
  1 |        1
  2 |        1
  3 |        1

=# \d customers
                                         Table "customers"
   Column   |            Type             |                         Modifiers
------------+-----------------------------+-----------------------------------------------------------
 id         | integer                     | not null default nextval('customers_id_seq'::regclass)
 name       | character varying(255)      |
...

=# select id from customers;
 id
----
  1
(1 row)

!!!! Only 1 record with ID = 1 !!!!

##### DEF #####
class Order < ActiveRecord::Base
        validates_presence_of :quote

        belongs_to :approved, :class_name => "Customer", :foreign_key => "id"
#        has_one :remover, :class_name => "Customer", :foreign_key => "id"
end

.. Somewhere in .erb ..
<% @orders.each do |order| %>
...
   <%=h order.approved.name %>
...

#### RESULT: LOG ####
...
Rendering template within layouts/orders
Rendering orders/index
  Admin Load (0.5ms)   SELECT * FROM "customers" WHERE ("customers"."id" = 1)
  Admin Load (0.2ms)   SELECT * FROM "customers" WHERE ("customers"."id" = 2)

ActionView::TemplateError (You have a nil object when you didn't expect it!


#### RESULT : WEB #####
 Showing app/views/orders/index.html.erb where line #8 raised:

You have a nil object when you didn't expect it!
The error occurred while evaluating nil.nick

Extracted source (around line #8):

...
8: 		<span class="approver">Approved by <%=h quote.approved.name %></span>
....