title: validation for at least one checkbox
body: <p>I have seen a couple of other posts with the same question but couldn't get the solution to work for me so I'm posting my own question.</p>
  
  <p>Let me preface this by saying I'm new to JQuery and MVC. I have 3 checkboxes, and I need to ensure at least one of them is checked. I have something that is working using a Jquery custom validation. But it is displaying 3 messages in a Validation Summary. I want it to display only one message, and if possible not in a validation summary. How could I achieve this?</p>
  
  <p>html code</p>
  
  <pre><code>&lt;label for="river1"&gt;river1&lt;/label&gt;
  &lt;input checked="checked" class="checkbox" data-val="true" data-val-required="The     river1 field is required." id="river1" name="river1" type="checkbox" value="true" /&gt;
  &lt;input name="river1" type="hidden" value="false" /&gt;&lt;br /&gt;
  
  &lt;label for="river2"&gt;river2&lt;/label&gt;
  &lt;input checked="checked" class="checkbox" data-val="true" data-val-required="The river2 field is required." id="river2" name="river2" type="checkbox" value="true" /&gt;
  &lt;input name="river2" type="hidden" value="false" /&gt;&lt;br /&gt;
  
  &lt;label for="river3"&gt;river3&lt;/label&gt;
  &lt;input checked="checked" class="checkbox" data-val="true" data-val-required="The river3 field is required." id="river3" name="river3" type="checkbox" value="true" /&gt;
  &lt;input name="river3" type="hidden" value="false" /&gt;&lt;br /&gt;
  </code></pre>
  
  <p>JQuery</p>
  
  <pre><code>$.validator.addMethod("checkbox", function (value, element) {
    return $('.checkbox:checked').length &gt; 0;
    }, 'At least one river must be selected.');
  </code></pre>