title: Rails 3 ActiveAdmin CanCan. How to setup that User should only see records that belong to him?
body: <p>I setup admin_users that belongs to a customer class (Customer is a company). So Customer has many admin_users.</p>
  
  <p>I'm trying to restrict access to Shipment records that belongs to a certain customer. I don't want customers watching other customers data. So I set this up but it seems to do nothing...</p>
  
  <p>class Ability
        include CanCan::Ability</p>
  
  <pre><code>  def initialize(user)
      user ||= AdminUser.new       
      if user.role == "administrator"
          can :manage, :all
      else
        cannot :create, :all
        cannot :update, :all
        cannot :destroy, :all
        can :read, Shipment do |shipment|
          shipment.customer == user.customer
        end
      end
    end 
  end
  </code></pre>
  
  <p>And I do have this in shipments.rb ...</p>
  
  <pre><code>ActiveAdmin.register Shipment do
    menu :if =&gt; proc{ can?(:read, Shipment) }, :priority =&gt; 1
    controller.authorize_resource
  
    index do
      column "File #", :sortable =&gt; :file_number do |shipment|
        link_to shipment.file_number, admin_shipment_path(shipment)
      end
      [... more columns ...]
      default_actions if can? :manage, Shipment
    end
  
    show :title =&gt; :file_number do
    panel "Shipment Details" do
    attributes_table_for shipment do
      row("File number") {shipment.file_number}
      row("Mode") {shipment.mode}
      row("Ocean Rate") { number_to_currency shipment.ocean_rate}
      row("Customer") { link_to shipment.customer.company_name, admin_customer_path(shipment.customer)}
      row("Shipper") { link_to shipment.shipper.company_name, admin_shipper_path(shipment.shipper)}
      row("Broker") { link_to shipment.broker.company_name, admin_broker_path(shipment.broker)}
    end
  end
  
  [...more show action stuff...]
  </code></pre>
  
  <p>So in the index page, all shipments get displayed and if I'm logged in as Customer A and click on Customer B's shipment I can see it, but it's supposed to block me.</p>
  
  <p>More info...</p>
  
  <pre><code>shipments_controller.rb
  class ShipmentsController &lt; InheritedResources::Base
    before_filter :authenticate_admin_user!
  end
  </code></pre>