gistfile1.php

<?php

// MongoDB Model

class MongoTest extends Moloquent {
	
	protected $connection = 'mongodb';
	
	protected $collection = 'test';
	
	public function mysql() {
		return $this->belongsTo('MysqlTest', 'test_id');
	}
	
}

// MySQL Model

class MysqlTest extends \Jenssegers\Mongodb\ModelCross {
	
	protected $connection = 'mysql';
	
	protected $table = 'test';
	
	public function mongo() {
		return $this->hasMany('MongoTest', 'test_id');
	}
	
}

// Method to test

	public function mongo() {
		$mongo = MongoTest::all()->first();
		echo '<h1>Mongo with MySQL relation</h1>';
		echo '<pre>' . $mongo . "\n" . $mongo->mysql . '</pre>';
		$mysql = MysqlTest::all()->first();
		echo '<h1>MySQL with Mongo relation</h1>';
		echo '<pre>' . $mysql . "\n" . $mysql->mongo . '</pre>';
	}
	
// Example: http://laravel.ollieread.com/mongo