Mongoose $AddFields添加数组而不是单个值

我使用以下代码，其中根据购买对象中的

软件

值添加

soft_id

字段，但不幸的是，它通过获取所有现有软件的id添加了一个数组

const user = await User.aggregate()
        .match({ _id: ObjectId(id) })                       
        .addFields({                
            'purchased.soft_id': '$purchased.software'
        })

    res.send(user);

这是我使用上述代码后得到的输出

{
    "_id": "5f6f71685c370b1bec3763fc",
    "role": "user",
    "email": "ab137@12345.com",
    "password": "test123",
    "purchased": [
        {
            "software": "5f6e47eb92d318037c0a6e50",
            "expiredAt": "1970-01-19T12:32:40.241Z",
            "soft_id": [
                "5f6e47eb92d318037c0a6e50",
                "5f5d410d61fea800f01d8714",
                "5f6f804490b35a0398c64cd5"
            ]
        },
        {
            "software": "5f5d410d61fea800f01d8714",
            "expiredAt": "1970-01-19T12:32:40.241Z",
            "soft_id": [
                "5f6e47eb92d318037c0a6e50",
                "5f5d410d61fea800f01d8714",
                "5f6f804490b35a0398c64cd5"
            ]
        },
        {
            "software": "5f6f804490b35a0398c64cd5",
            "expiredAt": "1970-01-19T12:32:40.241Z",
            "soft_id": [
                "5f6e47eb92d318037c0a6e50",
                "5f5d410d61fea800f01d8714",
                "5f6f804490b35a0398c64cd5"
            ]
        }
    ],
    "createdAt": "2020-09-26T16:50:48.872Z",
    "updatedAt": "2020-09-26T17:54:19.208Z",
    "__v": 0
}
]

---

它无法访问对象元素的直接数组，您需要使用一些数组运算符，如

$map

• $map

  迭代循环，添加新字段

  soft\u id

  ，值为

  software

  ，并使用

  $mergeObjects

  合并对象

const user = await User.aggregate()
    .match({ _id: ObjectId(id) })                       
    .addFields({                
        purchased: {
            $map: {
                input: "$purchased",
                in: {
                    $mergeObjects: [
                        "$$this",
                        { soft_id: "$$this.software" }
                    ]
                }
            }
        }
    });

    res.send(user);