Codeigniter : $this->session->userdata('user_id') not working - php

Question

So i'm trying to learn using codeigniter 3, and i'm trying to get the id from users table, the name of the id column on users table is user_id, and i have another table called lowongan, it has id_user to get the id(user_id) from the users table. So when i tried to input and submit that input to be saved into the database, the id_user is null, but i already set it like this
$id_user = $this->session->userdata('user_id');
$data = array(
'id_user' => $id_user
);
But it's still null how can i fix this??
The model :
<?php
class M_lowongan extends CI_Model{
public function show_lowongan(){
return $this->db->get('lowongan');
}
public function input_data($data, $table){
$this->db->insert($table, $data);
}
}
The Controller :
public function store_lowongan(){
$id_user = $this->session->userdata('user_id');
$title = $this->input->post('title');
$lokasi = $this->input->post('lokasi');
$level_pekerja = $this->input->post('level_pekerja');
$pengalaman_kerja = $this->input->post('pengalaman_kerja');
$pendidikan = $this->input->post('pendidikan');
$alamat = $this->input->post('alamat');
$no_wa = $this->input->post('no_wa');
$no_telp = $this->input->post('no_telp');
$min_gaji = $this->input->post('min_gaji');
$max_gaji = $this->input->post('max_gaji');
$job_desc = $this->input->post('job_desc');
$data = array(
'id_user' => $id_user,
'title' => $title,
'lokasi' => $lokasi,
'level_pekerja' => $level_pekerja,
'pengalaman_kerja' => $pengalaman_kerja,
'pendidikan' => $pendidikan,
'alamat' => $alamat,
'no_wa' => $no_wa,
'no_telp' => $no_telp,
'min_gaji' => $min_gaji,
'max_gaji' => $max_gaji,
'job_desc' => $job_desc
);
$this->m_lowongan->input_data($data, 'lowongan');
redirect ('dashboard');
}

Answer 1

do you already create the session? If not, you can create like this:
$row = $this->Auth_model->get_by_username($this->input->post('username'));
$session = array(
'id_users' => $row->id_users,
'name' => $row->name,
'username' => $row->username,
'email' => $row->email,
'usertype' => $row->usertype,
'photo' => $row->photo,
'photo_thumb' => $row->photo_thumb,
);
$this->session->set_userdata($session);
After that you can easily call the session like:
$this->session->name