title: set param value in rails form_for method
body: <p>How can I set the value of an attribute (called 'type') that I don't want to appear in a form? (i.e. I don't want the user to be able to select it in the form. I want to set the value myself).</p>
  
  <p>My form code is:</p>
  
  <pre><code>&lt;%= form_for @unit do |f| %&gt;
  
       &lt;%= f.datetime_select :start_datetime %&gt;
       &lt;%= f.text_field :notes %&gt;
  
  &lt;% end %&gt;
  </code></pre>
  
  <p>This generates params of:</p>
  
  <pre><code>{'unit' =&gt; {'start_datetime' =&gt; value, 'notes' =&gt; value }}
  </code></pre>
  
  <p>I want to set the 'type' attribute (to some value that I determine) so that the form returns params of:</p>
  
  <pre><code>{'unit' =&gt; {'type' =&gt; value, 'start_datetime' =&gt; value, 'notes' =&gt; value }}
  </code></pre>
  
  <p>Does form_for have some option that I can use to include 'type' in params and set its value?</p>