如何将laravel模型保存到2个数据库中

'connections' => [
    // 默认数据库连接
    'mysql' => [
        'driver' => 'mysql',
        'host' => env('DB_HOST', '127.0.0.1'),
        'port' => env('DB_PORT', '3306'),
        'database' => env('DB_DATABASE', 'forge'),
        'username' => env('DB_USERNAME', 'forge'),
        'password' => env('DB_PASSWORD', ''),
        'charset' => 'utf8mb4',
        'collation' => 'utf8mb4_unicode_ci',
        'prefix' => '',
        'strict' => true,
        'engine' => null,
    ],

    // 第二个数据库连接
    'secondary' => [
        'driver' => 'mysql',
        'host' => env('DB_SECONDARY_HOST', '127.0.0.1'),
        'port' => env('DB_SECONDARY_PORT', '3306'),
        'database' => env('DB_SECONDARY_DATABASE', 'forge'),
        'username' => env('DB_SECONDARY_USERNAME', 'forge'),
        'password' => env('DB_SECONDARY_PASSWORD', ''),
        'charset' => 'utf8mb4',
        'collation' => 'utf8mb4_unicode_ci',
        'prefix' => '',
        'strict' => true,
        'engine' => null,
    ],
],

DB_SECONDARY_HOST=127.0.0.1
DB_SECONDARY_PORT=3306
DB_SECONDARY_DATABASE=secondary_db
DB_SECONDARY_USERNAME=root
DB_SECONDARY_PASSWORD=secret

$user = new User;
$user->name = 'John Doe';
$user->email = 'john@example.com';
$user->save();

$user->on('secondary')->save();