名称xxx在当前上下文中不存在。我究竟做错了什么？

 var result = from lr in _db.LeaveRequest
                 join th in _db.TotalHourslu    
                 on lr.TotalHoursEffect 
                 equals th.Minutesselect
                     select new { lr.TotalHoursEffect, th.Minutes, tr.Display };
 var result = from lr in _db.LeaveRequest