title: Ext js sorting custom column by contents
body: <p>I have a grid in ext with some custom columns, and I want to be able to sort this column - I want to sort it by what is displayed inside of it, but really I just cannot figure out how to define a sorter for a column that will not be based on the dataIndex - I tried using a custom model, but I could not get that to work.</p>
  
  <pre><code>{
      text: 'Parent',
      dataIndex: 'Parent',
      renderer: function(value, meta, record) {
          var ret = record.raw.Parent;
          if (ret) {
              return ret.Name;
          } else {
              meta.tdCls = 'invisible';
              return record.data.Name;
          }
      },
      sortable: true
  },
  </code></pre>