如何在codeigniter中引用数据库连接？

$db['default'] = array(
	'dsn'	=> '',
	'hostname' => 'localhost',
	'username' => 'your_username',
	'password' => 'your_password',
	'database' => 'your_database_name',
	'dbdriver' => 'mysqli',
	'dbprefix' => '',
	'pconnect' => FALSE,
	'db_debug' => (ENVIRONMENT !== 'production'),
	'cache_on' => FALSE,
	'cachedir' => '',
	'char_set' => 'utf8',
	'dbcollat' => 'utf8_general_ci',
	'swap_pre' => '',
	'encrypt' => FALSE,
	'compress' => FALSE,
	'stricton' => FALSE,
	'failover' => array(),
	'save_queries' => TRUE
);

class Example_controller extends CI_Controller {

	public function __construct() {
		parent::__construct();
		$this->load->database();
	}

	public function index() {
		// 使用$this->db对象执行数据库操作
	}
}

class Example_model extends CI_Model {

	public function __construct() {
		parent::__construct();
	}

	public function get_data() {
		// 使用$this->db对象执行数据库操作
	}
}

$query = $this->db->query("SELECT * FROM your_table_name");
$result = $query->result();

$data = array(
	'column1' => 'value1',
	'column2' => 'value2'
);
$this->db->insert('your_table_name', $data);

$data = array(
	'column1' => 'new_value1',
	'column2' => 'new_value2'
);
$this->db->where('id', $id);
$this->db->update('your_table_name', $data);

$this->db->where('id', $id);
$this->db->delete('your_table_name');