title: ruby on rails: ensure user must enter value before submittal
body: <p>I have a form in rails using &lt;%= form_for... %> and I was wondering what do I need to do so that the user has to submit values before submitting?</p>
  
  <p>I have input field, radio buttons, and checkbox.</p>
  
  <pre><code>&lt;%= form_for @user, :html =&gt; {:multipart =&gt; true} do |f| %&gt;
    &lt;%= f.text_field :textfield %&gt;
    &lt;%= f.check_box :checkbox %&gt;
    &lt;%= f.radio_button :radiobutton %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>How do I tell my form that <code>:textfield</code>, <code>:checkbox</code>, and <code>:radiobutton</code> needs to be filled out or checked or something before submitting?</p>
  
  <p>Thanks!</p>