title: Adding a custom input field in formtastic?
body: <p>I can't figure out, or find any solutions to a very simple question:
  "How can I define my own input field in formtastic?"</p>
  
  <p>This is what I got:</p>
  
  <pre><code>&lt;%= semantic_form_for @someFantasticVariable, :url =&gt; "/someFantasticUrl.html" do |f|%&gt;  
      &lt;%= f.inputs do %&gt;
          &lt;%= f.input :something_else_id, :required =&gt; true , :as =&gt; :select, :collection   =&gt; SomethingElse.find(:all), :label =&gt;"The something else"%&gt;
          &lt;%= f.input :fantastic_max_cost, :label =&gt; "Budget (max cost)"%&gt;  
      &lt;%end%&gt;
  
  
      &lt;%= f.buttons do%&gt;
          &lt;%= f.commit_button :button_html =&gt; { :class =&gt; "primary", :disable_with =&gt;     'Processing...', :id =&gt; "commitButton"}%&gt;
      &lt;%end%&gt;
  &lt;%end%&gt;
  </code></pre>
  
  <p>Now..</p>
  
  <p>I want to have a very simple thing. I want to ad a field that is not part of the model. I want to have a date field that I can use to calculate some stuff in my controller. So I want to do this:</p>
  
  <pre><code>&lt;%= f.inputs do %&gt;
      &lt;%= f.input :something_else_id, :required =&gt; true , :as =&gt; :select, :collection   =&gt; SomethingElse.find(:all), :label =&gt;"The something else"%&gt;
      &lt;%= f.input :fantastic_max_cost, :label =&gt; "Budget (max cost)"%&gt;  
      &lt;%= f.input :start_date, :as =&gt; :date , :label =&gt; "Start date"%&gt;
  &lt;%end%&gt;
  </code></pre>
  
  <p>But apparetly I'm not allowed, and I can't find any way to do this through my thrusted googling. Any help / ideas?</p>