node.js - 如何在 MongoDB 中 $unset 整个对象而不是将其保留为空或 null

Question

我有以下更新查询，它会删除对象的内容，但它会留下空。我想删除整个对象{}。

我怎样才能做到这一点？我也尝试过为 properties 指定 value 而不是 booleans，这给了我相同的结果。

如果我执行此操作 { $unset: { "courses.1.teachers.1": 1 }，则会返回 null 而不是 {}。所以它们都不是最佳的。

student.updateStudent = (fcallback) => {
    var studentObjectId = global.mongoId("5a019896f89c24926108e2bf")
    global.db.collection('students').updateOne({ "_id": studentObjectId }, { $unset: { "courses.1.teachers.1.firstName": 1, "courses.1.teachers.1.lastName": 1 } }, (err, result) => {
        if (err) {
            var jError = { "status": "error", "message": "ERROR -> user.js -> 001" }
            console.log(jError)
            return fcallback(true, jError)
        }
        var jOk = { "status": "ok", "message": "user.js -> deleted -> 000" }
        console.log(jOk)
        console.log(JSON.stringify(result))
        return fcallback(false, jOk)
    })
}

这是留下空对象的结果:

{
    "_id" : ObjectId("5a019896f89c24926108e2bf"),
    "firstName" : "Sarah",
    "lastName" : "Jepsen",
    "age" : 27,
    "courses" : [ 
        {
            "courseName" : "Web-development",
            "teachers" : [ 
                {
                    "firstName" : "Santiago",
                    "lastName" : "Donoso"
                }
            ]
        }, 
        {
            "courseName" : "Databases",
            "teachers" : [ 
                {
                    "firstName" : "Dany",
                    "lastName" : "Kallas"
                }, 
                {} //see here
            ]
        }, 
        {
            "teachers" : [ 
                {
                    "firstName" : "Roxana",
                    "lastName" : "Stolniceanu"
                }
            ]
        }
    ]
}

我想要的是这样的:

{
    "_id" : ObjectId("5a019896f89c24926108e2bf"),
    "firstName" : "Sarah",
    "lastName" : "Jepsen",
    "age" : 27,
    "courses" : [ 
        {
            "courseName" : "Web-development",
            "teachers" : [ 
                {
                    "firstName" : "Santiago",
                    "lastName" : "Donoso"
                }
            ]
        }, 
        {
            "courseName" : "Databases",
            "teachers" : [ 
                {
                    "firstName" : "Dany",
                    "lastName" : "Kallas"
                }
            ]
        }, 
        {
            "teachers" : [ 
                {
                    "firstName" : "Roxana",
                    "lastName" : "Stolniceanu"
                }
            ]
        }
    ]
}

Answer 1

根据$unset docs ，这是所需的行为:

When used with $ to match an array element, $unset replaces the matching element with null rather than removing the matching element from the array. This behavior keeps consistent the array size and element positions.

所以您使用了错误的工具来完成这项工作。

正确的工具:

1. $pop运算符:删除第一个或最后一个数组元素
2. $pull运算符:根据条件删除项目

文档示例:

{
    "_id" : ObjectId("5a019896f89c24926108e2bf"),
    "firstName" : "Sarah",
    "lastName" : "Jepsen",
    "age" : 27,
    "courses" : [ 
        {
            "courseName" : "Web-development",
            "teachers" : [ 
                {
                    "firstName" : "Santiago",
                    "lastName" : "Donoso"
                }
            ]
        }, 
        {
            "courseName" : "Databases",
            "teachers" : [ 
                {
                    "firstName" : "Dany",
                    "lastName" : "Kallas"
                }, 
                {
                    "firstName": "Code",
                    "lastName": "Dragon"
                }
            ]
        }, 
        {
            "teachers" : [ 
                {
                    "firstName" : "Roxana",
                    "lastName" : "Stolniceanu"
                }
            ]
        }
    ]
}

示例 1:$pop:

global.db
    .collection('students')
    .updateOne(
        { _id : studentObjectId },
        { $pop: { "courses.1.teachers": 1 } } // 1 for last item, -1 for the first
    )

示例 2:$pull:

global.db
    .collection('students')
    .updateOne(
        { _id  : studentObjectId },
        { $pull: { "courses.1.teachers": { firstName: 'Code' } } }
    )