title: how to set grid's column dataindex like depart.name
body: <p>I have two classes</p>
  
  <pre><code>public class Employee
  {
      int id;
      String name;
      Depart depart;
  }
  
  public class Depart
  {
      int id;
      String name;
  }
  </code></pre>
  
  <p>so i query the employee data back to the extjs like</p>
  
  <pre><code>{total:2,list:[{"id":1,,"name":"jack",depart:{"id":1,"name":"departA"},{"id":2,,"name":"rose",depart:{"id":2,"name":"departB"}}
  </code></pre>
  
  <p>i set model like </p>
  
  <pre><code>{
      ....
  
      {
          type: 'string',
          name: 'depart.name'
      }    
  
      ....
  }
  </code></pre>
  
  <p>in the grid's column,i set like this</p>
  
  <pre><code>{
      ...
      dataIndex: 'depart.name',
      ...
  }
  </code></pre>
  
  <p>but the grid's column can't show the depart's name, how to do?
  thanks!</p>