using mysql function in update function's config virable

[eluser]杨帅[/eluser]
i use the following code to update a record in my database, but i want to use the mysql now() function in the config variable $data, the following syntaz output error, cuz php thought now() is a php function, and it cannot find it. if i surround quotes on now() as

Code:

'last_edit_time'=>'now()';

it also output error, cuz mysql thought "now()" is a string ,and it cannot be insert into a datetime collum in the database. anyone know how to solve this problem?

Code:

$data=array(
        'name'=>$name,
        'sex'=>$sex,
        'work_experience'=>$work_experience,
        'last_edit_time'=>now();
    );
            
        $username=$this->session->userdata('username');    
            
        $this->db->where('username', $username);
    $this->db->update('person', $data);