class User extends CI_Controller
{
 function index()
 {
  $this->load->model('login_model');
  $data['user'] = $this->login_model->get_user();
  $data['tweets'] = $this->tweet_model->usertweets();
  $this->load->view('templates/header');
  $this->load->view('user', $data);
  $this->load->view('templates/footer');
 }
}

class Login_model extends CI_Model
{
 function can_login($username, $password)
{
 $this->db->where('username', $username);
 $this->db->where('password', $password);
 $query = $this->db->get('users');

 //SELECT * FROM users WHERE username = '$username' AND password = '$password'

 if($query->num_rows() > 0)
 {
  return true;
 }
 else {
  return false;
 }
}

 function get_user()
 {
  $query = $this->db->get('users');

  $username = $_SESSION['username'];
  $this->db->select('user_id', 'first_name', 'last_name', 'date_joined');
  $this->db->from('users');
  $this->db->where('username', $username);
  $query = $this->db->get();
  return $query->row();
 }
}

class Tweet_model extends CI_Model
{
public function __construct()
{
    $this->load->database();
}

public function get_tweets($tweet_id = false)
{
    if ($tweet_id === false) {
        $this->db->join('users', 'tweets.user_id = users.user_id');
        $query = $this->db->get('tweets');
        return $query->result_array();
    }

    $query = $this->db->get_where('tweets', array('tweet_id' => $tweet_id));
    return $query->row_array();
}

public function set_tweet()
{
    $tweet = url_title($this->input->post('tweet'), 'dash', true);

    $query = $this->db->get('users');

    $username = $_SESSION['username'];
    $this->db->select('user_id');
    $this->db->from('users');
    $this->db->where('username', $username);

    if ($this->db->affected_rows())
    {
        $user = $query->row();
        var_dump($user_id);
    }

    $data = array(
      'tweet' => $this->input->post('tweet'),
      'user_id' => $user->user_id
    );

    return $this->db->insert('tweets', $data);
}

function Usertweets() {
  $this->db->flush_cache();

  $username = $_SESSION['username'];
  $this->db->select('user_id');
  $this->db->from('users');
  $this->db->where('username', $username);

  $query = $this->db->get();
  $user = $query->row();

  $this->db->flush_cache();

  $this->db->select('*');
  $this->db->from('tweets');
  $this->db->where('user_id', $user->user_id);

  return $this->db->get()->result();

}
}

<div class="container">
 <div class="row">
  <div class="col-md-4">
   <h4><?php echo $_SESSION['username']; ?></h4>
  </div>
  <div class="col-md-8">
   <?php foreach ($tweets as $tweet): ?>
    <div class="user-tweet">
     <h4><?php echo $_SESSION['username']; ?></h4>
     <h6><?php echo $tweet->tweet_date; ?></h6>
     <p><?php echo $tweet->tweet; ?></p>
    </div>
   <?php endforeach; ?>
  </div>
 </div>
</div>