title: simple_form default value with association
body: <p>This didn't work me: <a href="https://stackoverflow.com/questions/6477942/rails-default-selected-radiobutton-in-simpleform-collection">Rails - Default selected radiobutton in SimpleForm :collection</a></p>
  
  <p>I am trying to have a default selection. </p>
  
  <p>I have the following input in my form using simple_form</p>
  
  <pre><code>= f.association :collection_page
  </code></pre>
  
  <p>This generates a drop down with all the titles in my CollectionPage object. </p>
  
  <p>Kinda like:</p>
  
  <ul>
  <li>title1</li>
  <li>title2</li>
  <li>title3</li>
  </ul>
  
  <p>lets say, @collection_page.title = title1</p>
  
  <p>if I do:</p>
  
  <pre><code>= f.association :collection_page, as: :radio, :checked =&gt; @collection_page.title
  </code></pre>
  
  <p>title1 should be selected by default, but it isn't working for me. </p>
  
  <p>Thank you in advance for your help. </p>