title: How to make associations work in built and unsaved objects?
body: <p>Let's say I have something like:</p>
  
  <pre><code>@order = Order.new(status: :pending)
  
  @item  = @order.items.build(title: "Shirt")
  </code></pre>
  
  <p>When I try to call <code>@item.order</code>, I get an error not found, I guess it's because it's still unsaved to the DB, but how can make it point to the built object without saving any of the objects?</p>
  
  <pre><code>@item.order # Not Found - Tries to fetch from the DB
  </code></pre>