使用猫鼬“填充”时遇到问题答案

【问题标题】：Trouble using mongoose 'Populate'使用猫鼬“填充”时遇到问题
【发布时间】：2020-02-23 00:21:12
【问题描述】：

早安，

所以我似乎在用 Node.js 和 Mongoose 填充我的字段时遇到了问题。它只是打开一个空白数组：

结果：(JSON)

[
    {
        "courseassignments": [],
        "_id": "5db56ceb4cc2c92824ae2651",
        "name": "Garibaldi",
        "website": "www.garibaldi.org.uk",
        "__v": 0
    },
    {
        "courseassignments": [],
        "_id": "5db56d074cc2c92824ae2652",
        "name": "Kirk Hallam",
        "website": "www.kirkhallamacademy.co.uk",
        "__v": 0
    }
]

下面是我使用调用填充函数的代码，以及我用于每个数据的模型。这很奇怪。

*school.js（模型）*

// Require modules within our file:
const mongoose = require('mongoose')

const schoolSchema = new mongoose.Schema({
    name: {
        type: String,
        required: true,
        unique: true,
        trim: true
    },
    website: {
        type: String,
        required: true,
        trim: true
    },
    logo: {
        type: Buffer
    },
    courseassignments: [{
        type: mongoose.Schema.Types.ObjectID, 
        ref: 'CourseAssignment'
    }]
})

// Export the user to use within other files:
const school = mongoose.model('School', schoolSchema)
module.exports = school

courseassignment.js（模型）

// Require modules within our file:
const mongoose = require('mongoose')

const courseAssignmentSchema = new mongoose.Schema({
    school: {
        type: mongoose.Schema.Types.ObjectID,
        required: true,
        ref: 'School'
    },
    course: {
        type: mongoose.Schema.Types.ObjectID,
        required: true,
        ref: 'Course'
    }
})

// Export the user to use within other files:
const courseAssignment = mongoose.model('CourseAssignment', courseAssignmentSchema)
module.exports = courseAssignment

* 获取数据的代码：（在 app.js 中）*

router.get('/school', async (req, res) => {

    const schools = await School.find({}).populate({ path: 'courseassignments' })
    res.send(schools)

})

【问题讨论】：

标签： javascript node.js mongodb mongoose

【解决方案1】：

我会从 School 模型中删除 courseassigment 引用，并会利用虚拟填充。

以下是步骤：

school.js（学校模型 - 如您所见，我删除了课程分配参考，并添加了虚拟功能选项）

const mongoose = require('mongoose')

const schoolSchema = new mongoose.Schema({
    name: {
        type: String,
        required: true,
        unique: true,
        trim: true
    },
    website: {
        type: String,
        required: true,
        trim: true
    },
    logo: {
        type: Buffer
    }
}, {
    toJSON: { virtuals: true },
    toObject: { virtuals: true }
})

schoolSchema.virtual("courseassignments", {
    ref: "CourseAssignment",
    foreignField: "school",
    localField: "_id"
})

const school = mongoose.model('School', schoolSchema)
module.exports = school

此时，当您点击学校端点时，您的响应将是这样的。（我只展示了一个简短的项目。）

[
    {
        "_id": "5db5a809cfc9951770d5078a",
        "name": "school 1",
        "website": "school 1 website",
        "__v": 0,
        "courseassignments": [
            {
                "_id": "5db5a892cfc9951770d50790",
                "school": "5db5a809cfc9951770d5078a",
                "course": "5db5a847cfc9951770d5078d",
                "__v": 0
            },
            {
                "_id": "5db5a89ccfc9951770d50791",
                "school": "5db5a809cfc9951770d5078a",
                "course": "5db5a851cfc9951770d5078e",
                "__v": 0
            },
            {
                "_id": "5db5a8a1cfc9951770d50792",
                "school": "5db5a809cfc9951770d5078a",
                "course": "5db5a858cfc9951770d5078f",
                "__v": 0
            }
        ],
        "id": "5db5a809cfc9951770d5078a"
    },
    ...
    ...
]

如果您还想访问课程名称（我认为这很好），

courseassigment.js

const mongoose = require('mongoose')

const courseAssignmentSchema = new mongoose.Schema({
    school: {
        type: mongoose.Schema.Types.ObjectID,
        required: true,
        ref: 'School'
    },
    course: {
        type: mongoose.Schema.Types.ObjectID,
        required: true,
        ref: 'Course'
    }
}, {
    toJSON: { virtuals: true },
    toObject: { virtuals: true }
})

courseAssignmentSchema.pre(/^find/, function (next) {

    this.populate({
        path: 'course'
    });
    next();
});


// an index may be required like this
//courseAssignmentSchema.index({ school: 1, course: 1 }, { unique: true });

const courseAssignment = mongoose.model('CourseAssignment', courseAssignmentSchema)
module.exports = courseAssignment

结果将包含与课程相关的字段，例如课程名称。

[[
    {
        "_id": "5db5a809cfc9951770d5078a",
        "name": "school 1",
        "website": "school 1 website",
        "__v": 0,
        "courseassignments": [
            {
                "_id": "5db5a892cfc9951770d50790",
                "school": "5db5a809cfc9951770d5078a",
                "course": {
                    "_id": "5db5a847cfc9951770d5078d",
                    "name": "course 1",
                    "__v": 0
                },
                "__v": 0,
                "id": "5db5a892cfc9951770d50790"
            },
            {
                "_id": "5db5a89ccfc9951770d50791",
                "school": "5db5a809cfc9951770d5078a",
                "course": {
                    "_id": "5db5a851cfc9951770d5078e",
                    "name": "course 2",
                    "__v": 0
                },
                "__v": 0,
                "id": "5db5a89ccfc9951770d50791"
            },
            {
                "_id": "5db5a8a1cfc9951770d50792",
                "school": "5db5a809cfc9951770d5078a",
                "course": {
                    "_id": "5db5a858cfc9951770d5078f",
                    "name": "course 3",
                    "__v": 0
                },
                "__v": 0,
                "id": "5db5a8a1cfc9951770d50792"
            }
        ],
        "id": "5db5a809cfc9951770d5078a"
    },
    ...
    ...
]

文档：

https://mongoosejs.com/docs/tutorials/virtuals.html

https://mongoosejs.com/docs/populate.html#populate-virtuals

【讨论】：