const vador = new classes.Jedi({
  _id: 'vador',
  'firstName': 'Dark',
  'lastName': 'Vador'
});

const luke = new classes.Jedi({
  _id: 'luke',
  'firstName': 'Luke',
  'lastName': 'Skywalker'
});

// set father link
luke.father = vador;

db.export('Jedi');
// => '{\"vador\":{\"_id\":\"vador\",\"firstName\":\"Dark\",\"lastName\":\"Vador\"},
// \"luke\":{\"_id\":\"luke\",\"firstName\":\"Luke\",\"lastName\":\"Skywalker\",\"father\":\"@vador\"}}'