title: How to eager-load has_one associations on STI subclass
body: <p>I have a model hierarchy like this:</p>
  
  <pre><code>class Activity
  end
  
  class HelloActivity &lt; Activity
    has_one :hello_activity_details
  end
  
  class WorldActivity &lt; Activity
    has_one :world_activity_details
  end
  </code></pre>
  
  <p>I want to query all activities and eager load the details to avoid the N+1 issue. However, doing:</p>
  
  <pre><code>Activity.all.include([:hello_activity_details, :world_activity_details])
  </code></pre>
  
  <p>Yields</p>
  
  <pre><code>Association named 'hello_activity_details' not found on WorldActivity; perhaps you misspelled it?
  </code></pre>
  
  <p>How can I load the details?</p>
  
  <p>I know I can invoke the preloader manually, but is there a more idiomatic way.</p>
  
  <p>Thanks</p>