就是类似于 SELECT tp_user AS Owner, tp_user AS User 这样的，一个表起了两个别名，其中一个别名下的冲突字段改名？

class BorrowViewModel extends ViewModel {
public $viewFields = array(
'Borrow' => array(),
'Own' => array('_on' => 'Borrow.b_o_id = Own.o_id'),
'Machine' => array('_on' => 'Machine.m_id = Own.o_m_id'),
'User' => array(
'u_id' => 'ob_id',
'u_name' => 'ob_name',
'_as' => 'Owner',
'_on' => 'Owner.ob_id = Own.o_u_id'
),
'User' => array(
'_as' => 'User',
'_on' => 'User.u_id = Borrow.b_u_id'
),
);
}