Load database config file from libraries in CodeIgniter

Sometime you will need load database config variables from your libraries.In this case, if you use $this->_CI->config->load('database'), you will get an error:

$this->_CI = &get_instance();
$this->_CI->config->load('database');

The error somthing like Your application/config/database.php file does not appear to contain a valid configuration array.

The source is in system/core/Config.php#138:

// CodeIgniter Version 2.1.4

if ( ! isset($config) OR ! is_array($config))
			{
				if ($fail_gracefully === TRUE)
				{
					return FALSE;
				}
				show_error('Your '.$file_path.' file does not appear to contain a valid configuration array.');
			}

You can find that the config will lookup an array with the name $config, but in your database's config file it contains array variable with the name $db defaultly.This is the reason you got the invalid configuration array error message.

To correctly load database configuration from libraries,you can you code below:

$this->_CI->load->database('default');

$db = $this->_CI->db;

Something::config(['driver'=> 'mysql','host'=> $db->hostname,
    'dbname'=> $db->database,
    'user'=> $db->username,
    'password'=> $db->password]);

Notice the default is the active group in your database configuration file.