Many a times we need use multiple database as per the domain or some other reason . We can easily achieve it with the following code in cakePhp.

Write the following code in app->config->database.php

class DATABASE_CONFIG {

    public $default = array(
        'datasource' => 'Database/Mysql',
        'persistent' => false,
        'host' => 'localhost',
        'login' => 'root',
        'password' => '',
        'database' => 'firstDatabaseName',
        'prefix' => ''
    );
    public $first = array(
        'datasource' => 'Database/Mysql',
        'persistent' => false,
        'host' => 'localhost',
        'login' => 'root',
        'password' => '',
        'database' => 'firstDatabaseName',
        'prefix' => ''
    );
    public $second= array(
        'datasource' => 'Database/Mysql',
        'persistent' => false,
        'host' => 'localhost',
        'login' => 'root',
        'password' => '',
        'database' => 'seondDatabaseName',
        'prefix' => ''
    );

   public function __construct() {
        $parsed = parse_url($_SERVER['HTTP_HOST']);

       $domain = explode('.', $parsed['path']);
        $subdomain = '';
        if ($domain[0] == 'www')
            $subdomain = $domain[1];
        else
            $subdomain = $domain[0];
        if ($subdomain == 'us') {
            // use site one database config
            $this->default = $this->second;

            // elseif site two
        }else if($subdomain == 'can'){
           $this->default = $this->first; 
        }
    }

}