title: Select2 generating id with ajax response data
body: <p>My JSON response data does not contain an ID field, which is required by Select2 in order to display results. In the documentation they  provide a way to generate id, however, I was unable to do so. Can someone provide an example on how to do this? I have tried this so far:</p>
  
  <pre><code>  $('.itemSearch').select2(
       ajax: {
       type: "POST",
       url: '/Default.aspx/TestMethod',
       data: function(params){
         var query={
             message:params.term
         }
         return JSON.stringify(query);
       },
       processResults: function (data) {
                  var data1 = $.map(data, function (obj) {
                     obj.id = obj.id || obj.ItemNumber; // replace pk with your identifier
                     return obj;
                  });                         
        return {
           results: data.items,
        };
      }
     }
   });
  </code></pre>