Javascript 从mongodb中的2个集合中查找生成一个json

您能否帮助我从两个集合生成一个json：

用户[用户id、用户名、城市id]

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

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

城市[城市id、城市名称]

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

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

JSON如下所示：

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

---

您将需要在应用程序层中进行连接，在MongoDB中无法连接数据。任何时候，当您有两个集合中的数据时，您都必须发出两个查询。

我同意两个查询，但是，它如何在nodejs中正确写入？