猫鼬内的嵌套查询

Question

我有一个 Student.find 查询，它在 Room.find 查询中运行，如下所示：

Room.find({ schoolID:  mongoose.mongo.ObjectId(user.schoolID) }).sort({'level':'ascending','name':'ascending'}).then(function (roomList) {
  if (!roomList){
    console.log("no class room found")
  }else{
    console.log("class room found: " + roomList.length)
    var studentList = []
    for (var i = 0; i < roomList.length; i++){
      console.log(i)
      console.log("class room id: " + roomList[i]._id)
      console.log("class room name: " + roomList[i].name)
      Students.find({ schoolID:  mongoose.mongo.ObjectId(user.schoolID), classRoomID:  mongoose.mongo.ObjectId(roomList[i]._id) }).sort({'firstName':'ascending'}).then(function (data) {
        if (!data){
          console.log("no data found")
          return res.status(200).send({success: true, msg: 'No data found.'});
        }else{
          console.log("214 ada data: " + data.length)
          studentList[i] = data
          console.log("studentList " + i)
          console.log(studentList[i])
        }
      });
    }
    res.json({success: true, token: 'JWT ' + token, id: user._id, user: user, classRoom: roomList, students: studentList});    
  }
});

在数据库中，有 6 个教室，每个班级的学生人数不同。在 console.log 中，我期待看到类似的内容：

class room id: 01
class room name: my first class
studentList 0:
list of students from first class

class room id: 02
class room name: my second class
studentList 1:
list of students from 2nd class

class room id: 03
class room name: my third class
studentList 2:
list of students from 3rd class

因为我假设 Student.find 将在我输出 console.log("class room name: + roomList[i].name) 后立即执行

但原来所有的console.log("class room id") 和console.log("class room name") 都是先打印出来的，然后好像只有Students.find 被执行了，因为我的输出是什么像这样：

class room id: 01
class room name: my first class
class room id: 02
class room name: my second class
class room id: 03
class room name: my third class
class room id: 04
class room name: my fourth class
class room id: 05
class room name: my fifth class
class room id: 06
class room name: my six class

list of students
list of students
list of students
list of students
list of students
list of students

如果是这种情况，我该如何进行正确的嵌套查询？

Answer 1

Room.find({ schoolID:  mongoose.mongo.ObjectId(user.schoolID) }).sort({'level':'ascending','name':'ascending'}).then(function (roomList) {
  if (!roomList){
    console.log("no class room found")
  }else{
    console.log("class room found: " + roomList.length)
    var promsies = [];
    if (roomList.length) return res.status(200).send({success: true, msg: 'No data found.'});
    for (var i = 0; i < roomList.length; i++){
      console.log(i)
      console.log("class room id: " + roomList[i]._id)
      console.log("class room name: " + roomList[i].name)
      promsies.push(Students.find({ schoolID:  mongoose.mongo.ObjectId(user.schoolID), classRoomID:  mongoose.mongo.ObjectId(roomList[i]._id) }).sort({'firstName':'ascending'}));
    }
    Promise.all(promsies).then(function (studentList) {
        res.json({success: true, token: 'JWT ' + token, id: user._id, user: user, classRoom: roomList, students: studentList});
      });
  }
});

Answer 2

Mongoose 查询不是承诺。他们有一个用于 co 的 .then() 函数 和 async/await 作为一种方便。如果你需要一个成熟的承诺， 使用 .exec() 函数。

试试：

Room.find({
  schoolID: mongoose.mongo.ObjectId(user.schoolID)
}).sort({
  'level': 'ascending',
  'name': 'ascending'
}).exec().then(function(roomList) {
  if (!roomList) {
    console.log("no class room found")
  } else {
    console.log("class room found: " + roomList.length)
    var studentList = []
    for (var i = 0; i < roomList.length; i++) {
      console.log(i)
      console.log("class room id: " + roomList[i]._id)
      console.log("class room name: " + roomList[i].name)
      Students.find({
        schoolID: mongoose.mongo.ObjectId(user.schoolID),
        classRoomID: mongoose.mongo.ObjectId(roomList[i]._id)
      }).sort({
        'firstName': 'ascending'
      }).exec().then(function(data) {
        if (!data) {
          console.log("no data found")
          return res.status(200).send({
            success: true,
            msg: 'No data found.'
          });
        } else {
          console.log("214 ada data: " + data.length)
          studentList[i] = data
          console.log("studentList " + i)
          console.log(studentList[i])
        }
      });
    }
    res.json({
      success: true,
      token: 'JWT ' + token,
      id: user._id,
      user: user,
      classRoom: roomList,
      students: studentList
    });
  }
});

您遇到的另一个问题是您正在尝试使用异步进行 for 循环。它不能那样工作......（for循环不会等待并且会继续运行）要么使用Promise.All，要么使用among these lines