如果用戶在用戶陣列中，如何使用貓鼬查詢查找

我正在嘗試找到一種方法來檢查學生是否使用貓鼬簽署了課程。

我有這些模式：

課程架構：

    const mongoose = require("mongoose");
    const User = require("../models/User");

    const CourseSchema = new mongoose.Schema(
     {
    courseName: { type: String, required: true, unique: true },
    teacher: {
      teacherName: { type: String },
      teacherID: {
        type: mongoose.Schema.Types.ObjectId,
        ref: "User",
      },
    },
    students: [
      {
        studentName: { type: String },
        studentID: {
          type: mongoose.Schema.Types.ObjectId,
          ref: "User",
        },
      },
    ],
    },
      { collection: "courses" },
     { timestamps: true }
     );

    module.exports = mongoose.model("Course", CourseSchema);

在這里，我將所有簽署課程的學生保存在學生物件陣列中。

學生模式：

const mongoose = require("mongoose");

const UserSchema = new mongoose.Schema(
  {
    username: { type: String, required: true, unique: true },
    email: { type: String, required: true, unique: true },
    password: { type: String, required: true },
    userType: {
      type: String,
      enum: ["student", "teacher"],
      default: "student",
    },
    isOnline: { type: Boolean, default: false },
  },
  { collection: "users" },
  { timestamps: true }
);
module.exports = mongoose.model("User", UserSchema);

現在我正在嘗試進行查詢，該查詢將回傳學生簽署的課程串列。

例如：

如果我有 3 門課程 = [數學、英語、編程] 并且有一個 id = 1 的學生為數學和英語簽名（在學生陣列中），那么查詢將回傳數學和英語課程。

我試過這個沒有成功（得到空值，但用戶在學生物件陣列中）：

router.post("/:id", async (req, res) => {
  try {
    // get user
    var user = await User.findOne({
      username: req.body.username,
      email: req.body.email,
      password: req.body.password,
    });
    // search user courses by user id.
    const coursesList = await Course.find({
      students: {
        $in: [{ studentID: user._id, studentName: user.username }],
      },
    });
    res.status(200).json(coursesList);
  } catch (err) {
    res.status(500).json(err.message);
  }
});

uj5u.com熱心網友回復：

你可以這樣做：

const coursesList = await Course.find({ "students.studentID": user._id });

作業示例

uj5u.com熱心網友回復：

如果您只想回傳匹配的用戶，則可以使用聚合管道。現場演示在這里

資料庫

[
  {
    "course": "Math",
    "students": [
      {
        studentID: "id_1",
        studentName: "Name 1"
      },
      {
        studentID: "id_2",
        studentName: "Name 2"
      }
    ]
  },
  {
    "course": "English",
    "students": [
      {
        studentID: "id_1",
        studentName: "Name 1"
      },
      {
        studentID: "id_3",
        studentName: "Name 3"
      }
    ]
  },
  {
    "course": "Programming",
    "students": [
      {
        studentID: "id_4",
        studentName: "Name 4"
      },
      {
        studentID: "id_5",
        studentName: "Name 5"
      }
    ]
  },
  
]

詢問

db.collection.aggregate([
  {
    $unwind: "$students"
  },
  {
    $match: {
      "students.studentID": "id_1"
    }
  }
])

結果

[
  {
    "_id": ObjectId("5a934e000102030405000000"),
    "course": "Math",
    "students": {
      "studentID": "id_1",
      "studentName": "Name 1"
    }
  },
  {
    "_id": ObjectId("5a934e000102030405000001"),
    "course": "English",
    "students": {
      "studentID": "id_1",
      "studentName": "Name 1"
    }
  }
]

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