MongoDB 聚合 - 重新映射内部文档

Question

如何在以下示例中重新映射内部文档：

db.customers.aggregate(
[
    {
        $project: {
            "_id": 0,
            "First Name": "customerDetails.firstName",
            "Last Name": "customerDetails.lastName",
            "Full Name": { $concat : [ "customerDetails.firstName", " ", "customerDetails.lastName" ] }
        }
    }
]

)

像这样 "$customer.firstName" 放置 $ 不起作用，而不是取内部字段 firstName 的值，基本上它不会返回任何内容.

customer集合的结构示例：

{
    "_id" : ObjectId("5fb3c41454742e0d3c9f7605"),
    "customerDetails" : {
        "firstName" : "Robert",
        "lastName" : "Green",
        "phoneNumber" : "0878712375",
        "email" : "robert.green@gmail.com"
    }
}

预期结果：

{
    "First Name": "Robert",
    "Last Name": "Green",
    "Full Name": "Robert Green"
}

实际结果：

{
    "First Name": "customerDetails.firstName",
    "Last Name": "customerDetails.lastName",
    "Full Name": "customerDetails.firstName customerDetails.lastName"
}

Answer 1

使用$ 引用字段，应该可以：

db.customers.aggregate(
[
    {
        $project: {
            "_id": 0,
            "First Name": "$customerDetails.firstName",
            "Last Name": "$customerDetails.lastName",
            "Full Name": { $concat : [ "$customerDetails.firstName", " ", "$customerDetails.lastName" ] }
        }
    }
]