选择文档的子文档，并在mongoDB中排除if属性

Question

我在mongoDb.中有以下文档结构

我希望能够只使用select，而不是all the courses中的teacher属性。我怎么能这么做？

我试过以下几种方法，但不起作用。我也希望当它找到result时，它会将它返回给console

我怎么能这么做？

    student.findCourses = (fcallback) => {
        var jCourses = {
            "courses": [
                {
                    "courseName": "Web-development"
                },
                {
                    "courseName": "Databases"
                },
                {
                    "courseName": "Databases"
                }
            ]
        }
    global.db.collection('students').find(({}, { jCourses: true, _id: false, firstName: false, lastName: false, age: false, teachers: false }).toArray, (err) => {

        if (err) {
            var jError = { "status": "error", "message": "ERROR -> student.js -> 001" }
            console.log(jError)
            return fcallback(true, jError)
        }
        var jOk = { "status": "ok", "message": "student.js -> found -> 000" }
        console.log(jOk)
        return fcallback(false, jOk)

    })
}

该文件：

 {
                "firstName": "Sarah",
                "lastName": "Jepsen",
                "age": 27,
                "courses": [
                    {
                        "courseName": "Web-development",
                        "teachers": [
                            {
                                "firstName": "Santiago",
                                "lastName": "Donoso"
                            }
                        ]
                    },

                    {
                        "courseName": "Databases",
                        "teachers": [
                            {
                                "firstName": "Dany",
                                "lastName": "Kallas"
                            },
                            {
                                "firstName": "Rune",
                                "lastName": "Lyng"
                            }
                        ]
                    },
                    {
                        "courseName": "Interface-Design",
                        "teachers": [
                            {
                                "firstName": "Roxana",
                                "lastName": "Stolniceanu"
                            }
                        ]
                    }
                ]
            }

结果应该如下所示：

     {
        "courses": [
            {
                "courseName": "Web-development"
            },
            {
                "courseName": "Databases"
            },
            {
                "courseName": "Databases"
            }
        ]
    }

Answer 1

您可以使用点语法。

就像这样：

global.db.collection('students').find({}, { "courses.courseName": true, _id: false }).toArray((err, docs) => {
    if (err) {
        var jError = { "status": "error", "message": "ERROR -> student.js -> 001" }
        console.log(jError)
        return fcallback(true, jError)
    }
    var jOk = { "status": "ok", "message": "student.js -> found -> 000" }
    console.log(jOk);
    console.log(docs); // Will print to the console the data that you want
    return fcallback(false, jOk)

})

它将只打印 courseName of courses。

芒果壳上的例子：

> db.users.find().pretty()
{
        "_id" : ObjectId("59ff442eb40a672f2223a14f"),
        "firstName" : "Sarah",
        "lastName" : "Jepsen",
        "age" : 27,
        "courses" : [
                {
                        "courseName" : "Web-development",
                        "teachers" : [
                                {
                                        "firstName" : "Santiago",
                                        "lastName" : "Donoso"
                                }
                        ]
                },
                {
                        "courseName" : "Databases",
                        "teachers" : [
                                {
                                        "firstName" : "Dany",
                                        "lastName" : "Kallas"
                                },
                                {
                                        "firstName" : "Rune",
                                        "lastName" : "Lyng"
                                }
                        ]
                },
                {
                        "courseName" : "Interface-Design",
                        "teachers" : [
                                {
                                        "firstName" : "Roxana",
                                        "lastName" : "Stolniceanu"
                                }
                        ]
                }
        ]
}
> db.users.find({}, {_id: 1, "courses.courseName": 1}).pretty()
{
        "_id" : ObjectId("59ff442eb40a672f2223a14f"),
        "courses" : [
                {
                        "courseName" : "Web-development"
                },
                {
                        "courseName" : "Databases"
                },
                {
                        "courseName" : "Interface-Design"
                }
        ]
}
> db.users.find({}, {_id: 0, "courses.courseName": 1}).pretty()
{
        "courses" : [
                {
                        "courseName" : "Web-development"
                },
                {
                        "courseName" : "Databases"
                },
                {
                        "courseName" : "Interface-Design"
                }
        ]
}