title: Statement Invalid in Rails Admin
body: <p>I'm using <a href="https://github.com/sferik/rails_admin" rel="nofollow">rails_admin</a> gem. It works fine when I open the admin panel from localhost but then I get this error whenever i tried to show the user inside rails admin panel.</p>
  
  <pre><code>ActiveRecord::StatementInvalid in RailsAdmin::Main#show
  
  PG::UndefinedColumn: ERROR:  column relationships.user_id does not exist
  LINE 1: ...LECT "relationships".* FROM "relationships" WHERE "relations...
                                                               ^
  : SELECT "relationships".* FROM "relationships" WHERE "relationships"."user_id" = $1
  </code></pre>
  
  <p>I realised this error might come from my User model</p>
  
  <pre><code>class User &lt; ActiveRecord::Base
    has_many :relationships
    has_many :active_relationships, class_name:  "Relationship",
                                    foreign_key: "follower_id",
                                    dependent:   :destroy
    has_many :passive_relationships, class_name:  "Relationship",
                                     foreign_key: "followed_id",
                                     dependent:   :destroy
    has_many :following, through: :active_relationships, source: :followed
    has_many :followers, through: :passive_relationships, source: :follower
  end
  </code></pre>
  
  <p>relationship.rb</p>
  
  <pre><code>class Relationship &lt; ActiveRecord::Base
    belongs_to :follower, class_name: "User"
    belongs_to :followed, class_name: "User"    
  end
  </code></pre>
  
  <p>I don't have any idea at all why at fist the error said the <code>relationship.user_id</code> does not exist. How can I fix this? Thanks in advance.</p>