/**
* 减小符合条件的记录的指定字段的值，返回更新的记录总数
*
* 该操作不会引发任何事件，也不会处理关联数据。
*
* @param mixed $conditions
* @param string $field
* @param int $decr
*
* @return mixed
*/
function decrField($conditions, $field, $decr = 1)
{
$field = $this->dbo->qfield($field, $this->fullTableName, $this->schema);
$decr = (int) $decr;
$row = array();
$this->_setUpdatedTimeFields($row);
list($pairs, $values) = $this->dbo->getPlaceholderPair($row, $this->fields);
$pairs = implode(',', $pairs);
if ($pairs) {
$pairs = ', ' . $pairs;
}
$whereby = $this->getWhere($conditions, false);
$sql = "UPDATE {$this->qtableName} SET {$field} = {$field}- {$decr}{$pairs} {$whereby}";
return $this->dbo->execute($sql, $values);
}
