title: Validating Observable Array, using Knockout.Validation
body: <p>We are building a Single Page Application using Knockout, Durandal &amp; Breeze.</p>
  
  <p>We have a observable array, &amp; want to validate whether it contains any value or not i.e. the text box accepting values has been provided with any value or not. I am trying to achieve this using Knockout.Validation plugin. </p>
  
  <p>Code for view model is-</p>
  
  <pre><code>withs = ko.observableArray([]).extend({ required: true }),
  </code></pre>
  
  <p>and HTML is</p>
  
  <pre><code>&lt;div class="col-lg-9"&gt;
     &lt;select multiple="true" 
          data-bind="options: entities, optionsValue: 'Id', optionsText: 'Name', 
                     selectedOptions: withs, select2: {}" 
          style="width: 249px; border-radius: 4px;"&gt;&lt;/select&gt;
  &lt;/div&gt;
  </code></pre>