How to update data using session in codeigniter - codeigniter-3

Question

This my code in codeigniter but it doesn't update in database, I'm beginner ni codeigniter, how could I fix this error, or what is wrong in my code?
THis is my Controller:
function edit() {
$role = $this->session->userdata('role');
$this->form_validation->set_rules('firstname', 'firstname', 'required|xss_clean');
$this->form_validation->set_rules('lastname', 'lastname', 'required|xss_clean');
if ($this->form_validation->run() == FALSE) {
//set page data
$data['title'] = 'Update Profile';
if($role!=''){
$data['admin'] = $this->M_user->get($this->session->userdata('user_id'));
}else{
$data['admin'] = $this->M_administrator->getAdmin($this->session->userdata('id_admin'));
}
$data['sitename'] = $this->M_website->getName();
$data['content'] = 'admin/myaccount/edit';
//parse template
$this->parser->parse('admin/template', $data);
} else {
if($role!=''){
if ($this->M_user->updateStatus($_POST['user_id'])) {
//SAVE ADMIN ACTION LOG
//save_admin_action(array('module' => Constant::AM_ACCOUNT, 'action' => Constant::AL_EDIT, 'title' => $this->form_validation['username'], 'object_id' => $id));
//redirect page
$this->session->set_flashdata('saved', TRUE);
redirect('admin/myaccount');
}
}else{
if ($this->M_administrator->updateStatus($_POST['id_admin'])) {
//SAVE ADMIN ACTION LOG
//save_admin_action(array('module' => Constant::AM_ACCOUNT, 'action' => Constant::AL_EDIT, 'title' => $this->form_validation['username'], 'object_id' => $id));
//redirect page
$this->session->set_flashdata('saved', TRUE);
redirect('admin/myaccount');
}
}
}
}
This is my model administrator:
function updateStatus($post, $id){
$data = array(
'firstname' => $post['firstname'],
'lastname' => $post['lastname']
);
$this->db->where('id_admin', $id);
if($this->db->update('admin', $data)){
return TRUE;
}else{
return FALSE;
}
}
user Model:
function updateStatus($post, $id){
$data = array(
'firstname' => $post['firstname'],
'lastname' => $post['lastname']
);
$this->db->where('user_id', $id);
if($this->db->update('user', $data)){
return TRUE;
}else{
return FALSE;
}
}

Answer 1

pass firstname and last name to your updatestatus model function if you are not getting that value in model so you are not able to change
print your query using $this->db->last_query(); to get query output and post your query here

Answer 2

Change your where clause to
$this->db->where('id_admin', $post);