db={"users":[{"_id":{"oid":"61a04f49909f8e972f5722f1"},"email":"1234@gmail.com","password":"$2b$10$g06lbwH4jNd4O9R/dbaqnus10iy1uhGeroge.bXkUeBxTSaVkR75a","albums_ids":["61a45889f3bedd5c1b7a9db4","61a45969f3bedd5c1b7a9db6"]}],"albums":[{"_id":{"oid":"61a45889f3bedd5c1b7a9db4"},"name":"Brasil 2014"},{"_id":{"oid":"61a45969f3bedd5c1b7a9db5"},"name":"Brasil 2015"},{"_id":{"oid":"61a45969f3bedd5c1b7a9db6"},"name":"Brasil 2016"}]}

db.users.aggregate([{$unwind:"$albums_ids"},{"$lookup":{"from":"albums","localField":"albums_ids","foreignField":"_id.oid","as":"albums"}},{$unwind:"$albums"},{$group:{_id:"$_id.oid",albums:{"$push":"$albums"}}}])