带连接的 Codeigniter 活动记录更新语句

这是我试图通过活动记录实现的查询：

UPDATE `Customer_donations` cd 
join Invoices i on i.cd_id = cd.cd_id 
set cd.amount = '4', cd.amount_verified = '1' 
WHERE i.invoice_id =  '13';

这是我对活动记录的尝试：

$data = array('cd.amount'=>$amount, 'cd.amount_verified'=>'1');
$this->db->join('Invoices i', 'i.cd_id = cd.cd_id')
     ->where('i.invoice_id', $invoiceId);


// update the table with the new data
if($this->db->update('Customer_donations cd', $data)) {
  return true;
}

这是实际生成的查询：

UPDATE `Customer_donations` cd 
SET `cd`.`amount` = '1', `cd`.`amount_verified` = '1' 
WHERE `i`.`invoice_id` =  '13'

为什么此活动记录语句不应用我的连接子句？

下面的解决方案怎么样？有点难看，但它达到了您在问题中的预期。

$invoiceId = 13;
$amount = 4;
$data = array('cd.amount'=>$amount, 'cd.amount_verified'=>'1');

$this->db->where('i.invoice_id', $invoiceId);

$this->db->update('Customer_donations cd join Invoices i on i.cd_id = cd.cd_id', $data);