+----------+----------------------------------+
| class_id | name                             |
+----------+----------------------------------+
| BBI2424  | Academic Writing                 |
| MTH3100  | Calculus                         |
| SIM4207  | Ethics In Computing              |
| SSE3304  | Software Design                  |
| SSK3118  | Data Structure and Algorithm     |
| SSK3408  | Database Application Development |
+----------+----------------------------------+

+----------+----------+------------+----------+---------+
| class_id | day      | start_time | end_time | type    |
+----------+----------+------------+----------+---------+
| MTH3100  | Tuesday  | 10:00:00   | 12:00:00 | lecture |
| MTH3100  | Thursday | 11:00:00   | 12:00:00 | lecture |
+----------+----------+------------+----------+---------+

public function beforeFilter()
{
    // load classes model alias as classes
    $this->load->model('classes_model', 'classes');
    $this->load->model('schedules_model','schedules');
}

/**
 * index
 *
 * listing data classes
 *
 * @access public
 * @return void
 */
public function index()
{
    // get data from database
    $content['classes'] = $this->classes->lists();

    // capture classes content to template
    $data['content'] = $this->view->fetch('classes/list', $content);

    // bind content to template
    $this->view->display('example_layout', $data);
}

public function lists()
{
    // get all data from table classes
    $this->db->join('schedules','schedules.class_id=classes.class_id');
    return $this->db->find_all('classes');
}

public function create()
{
    // load input library
    $this->load->library('input');
    $content['classes']=$this->classes->lists();

    // get input data & filter it
    $input = $this->input->post('data', true);

    // input data exist
    if ( $input !== false )
    {
        // insert new data to database
        if ( $this->schedules->create($input) )
            redirect('/schedules/index');
    }

    // capture form
    $data['content'] = $this->view->fetch('schedules/create',$content);

    // bind content to template
    $this->view->display('example_layout', $data);
}

public function create($input)
{

    // insert new data to table schedules
    return $this->db->insert('schedules', $input);
}

<form role="form" action="<?php echo CONF_BASE_PATH; ?>/schedules/create" method="post">
<div class="form-group">
<label for="data[class_id]">Class Id:</label>
<select class="form-control" name="data[class_id]">
    <?php foreach($classes as $class){ //this line code return class_id from Schedules instead. i want to return from Classes ?>
        <option value="<?php echo $class['class_id'] ?>"><?php echo $class['class_id'] ?></option>
    <?php } ?>
</select>
</div>