加入Linq参加DevExpress博览会

我在devexpress中使用持久类添加了两个数据表

 XPQuery<me_employee> EmployeeQuery = new XPQuery<me_employee>(XpoDefault.Session);
 XPQuery<mr_role> EmployeeRoleQuery = new XPQuery<mr_role>(XpoDefault.Session);
 var employees = from emp in EmployeeQuery join empRole in EmployeeRoleQuery on emp.me_role_pkey equals empRole.mr_pkey 
 select new { emp.me_pkey, empRole.mr_role_name };

抛出错误:

"Specified Method is not supported"

如何在Devexpress中使用linq连接

谢谢