title: active_admin - display a list of items that belongs to another item
body: <p>I am trying to display somehow the <code>line items</code> for the <code>order</code> in the active_admin <code>order show page</code>, no luck..</p>
  
  <p>here are the relations between models:</p>
  
  <p><strong>order.rb</strong></p>
  
  <pre><code>class Order &lt; ActiveRecord::Base
    has_many :line_items, :dependent =&gt; :destroy
    # ...
    validates :name, :address, :email, :presence =&gt; true
    validates :pay_type, :inclusion =&gt; PAYMENT_TYPES
  end
  </code></pre>
  
  <p><strong>line_item.rb</strong></p>
  
  <pre><code>class LineItem &lt; ActiveRecord::Base
    belongs_to :order
    belongs_to :product
    belongs_to :cart
  
    def total_price
      product.price * quantity
    end
  
  end
  </code></pre>
  
  <p><strong>active_admin order.rb</strong></p>
  
  <pre><code>ActiveAdmin.register Order do
  
    show do
      attributes_table :name, :email, :address, :pay_type, :created_at, :updated_at
    end
  end
  </code></pre>
  
  <p><strong>active_admin line_item.rb</strong></p>
  
  <pre><code>class LineItem &lt; ActiveRecord::Base
    belongs_to :order
    belongs_to :product
    belongs_to :cart
  
    def total_price
      product.price * quantity
    end
  
  end
  </code></pre>
  
  <p>when I click show order, it must display the items for this order.. In application's show file I did it with </p>
  
  <pre><code>&lt;%= render @order.line_items %&gt;
  </code></pre>
  
  <p><strong>_line_items.html.erb</strong></p>
  
  <pre><code>&lt;!-- START_HIGHLIGHT --&gt;
  &lt;% if line_item == @current_item %&gt;
      &lt;tr id="current_item"&gt;
    &lt;% else %&gt;
  &lt;tr&gt;
  &lt;% end %&gt;
  &lt;!-- END_HIGHLIGHT --&gt;
    &lt;td&gt;&lt;%= line_item.quantity %&gt;&amp;times;&lt;/td&gt;
    &lt;td&gt;&lt;%= line_item.product.title %&gt;&lt;/td&gt;
    &lt;td class="item_price"&gt;&lt;%= number_to_currency(line_item.total_price) %&gt;&lt;/td&gt;
  &lt;/tr&gt;
  </code></pre>
  
  <p>and the items are in the page, but in Active_Admin I don't know how to make it work.. Please help. Thank you for your time.</p>
  
  <p><strong>Solved</strong></p>
  
  <p>Thanks to bruno077  I managed to finally get the line_items in the order show_page in ActiveAdmin</p>
  
  <pre><code> show do |order|
  
    panel "Customer details" do
      attributes_table_for order, :first_name, :last_name, :card_type, :created_at, :ip_address
    end
  
    panel("Products for this order") do
      table_for(order.line_items) do
        column "Product" do |item| 
          item.product.title
        end
        column "Price" do |item| 
          item.product.price
        end
        column "Quantity" do |item| 
          item.quantity
        end
      end
    end
  end
  </code></pre>
  
  <p>I got the ID of the product for now, but it's not far from here to get what I want. Cheers!</p>