title: Rails Form Association Field Shows Object Instead of Name
body: <p>I have a form that edits an object with an association, but the select menu shows the associated object instead of the user-friendly name (i.e. <code>#&lt;User:0x007fdcac6da278&gt;</code> instead of <code>SeanPerryman</code>). How can I set the value for that association box to be a value associated with that object? </p>
  
  <pre><code>= simple_form_for(@captain) do |f|
    = f.error_notification
    = f.association :user 
    = f.input :name
    = f.association :world
    = f.button :submit
  </code></pre>
  
  <p>Looks like it is doing it for the World association, but not for the User association.</p>
  
  <p><img src="https://i.stack.imgur.com/Xr5jJ.png" alt="enter image description here"></p>
  
  <p>I've tried adding a value tag:</p>
  
  <pre><code>= f.association :user, :value =&gt; @captain.user.username
  </code></pre>
  
  <p>But that doesn't change the display, and inspecting the select box has no mention of the value tag that I added.</p>