Generate one json from find in 2 collections in mongodb

Question

Can you help me to generate one json from two collections:

Users [ user_id, user_name, city_id ]

[
    {
        "name": "Anton",
        "user_id": 1,
        "city_id": 1
    },
    {
        "name": "Vasiliy",
        "user_id": 2,
        "city_id": 2
    }
]

Cities [ city_id, city_name ]

[
    {
        "name": "Kharkov",
        "city_id": 1
    },
    {
        "name": "Kiev",
        "city_id": 2
    }
]

JSON Like this:

[
        {
            "user_name": "Anton",
            "city_name": "Kharkov",
            "user_id": 1,
        },
        {
            "user_name": "Vasiliy",
            "city_name": "Kiev",
            "user_id": 2,
        }
]

Answer 1

You'll need to do the join in your application layer, there is no way to join the data in MongoDB. Any time you have data in two collections you will have to issue two queries.