Adding external databases to settings.php using prefix

Question

As per the comments in settings.php:

/*
 * You can also use a reference to a schema/database as a prefix. This maybe
 * useful if your Drupal installation exists in a schema that is not the default
 * or you want to access several databases from the same code base at the same
 * time.
 * Example:
 * @code
 *   'prefix' => array(
 *     'default'   => 'main.',
 *     'users'     => 'shared.',
 *     'sessions'  => 'shared.',
 *     'role'      => 'shared.',
 *     'authmap'   => 'shared.',
 *   );
 * @endcode
 */

So if my current simple default looks like:

$databases = array (
  'default' => 
  array (
    'default' => 
    array (
      'database' => 'dev',
      'username' => 'dev',
      'password' => 'dev',
      'host' => 'localhost',
      'port' => '',
      'driver' => 'mysql',
      'prefix' => false,
    ),
  ),
);

How would I add two tables (table1 and table2) on another database (dev1) on localhost so that they are available to drupal?

Answer 1

If they're on the same mysql host (and you've got the appropriate permissions) you can access the tables by simply prefixing them with the schema name: otherdatabasename.tablename. You can even run queries joining across the two databases.

If they're on a different server you'll need to add a separate connection and specify it as part of the query by using the $options['target'] setting.