How to Retrieve session id

login.php

<?php
class Login extends MY_Controller
{
public function index()
{
$this->load->view('login_view');
}
public function user_login()
{

$this->form_validation->set_error_delimiters('<p class="text-danger">','</p>');
if($this->form_validation->run('login_rules'))
{
$email = $this->input->post('uemail');
$password = $this->input->post('upassword');

$this->load->model('loginmodel');
$login_id = $this->loginmodel->login_valid($email, $password);
if($login_id)
{
$this->session->set_userdata('user_id', $login_id);

return redirect('admin/dashboard');

}

else
{
echo "password do not match.";
}
}
else
{
$this->load->view('login_view');
}

}
}

?>
----------------------------------------------------------------------------------------------------------------------------------------------------------
propertymodel.php
<?php 
class Propertymodel extends CI_Model
{
public function property_list()
{
$user_id = $this->session->userdata('user_id');
$query = $this->db
->select('prop_name')
->from('properties')
->where('user_id', $user_id )
->get();

return $query->result();
}
}

?>