在foreach中的mongoose find（）

Question

我想根據數組中的某些條件查找文檔，例如：

subscriptions=[
{teacher: 'john', student:'david' ,course:'math'},
{teacher: 'john', student:'david' ,course:'english'},
{teacher: 'matt', student:'max' ,course:'math'}]

我想在Exam集中找到以下位置：老師，學生和課程都基於以下數組：

subscriptions.forEach(sub=>{
Exam.find({teacher:sub.teacer, student:sub.student, course:sub.course},(err,res)=>{})})

誰不能在for循環中調用find，我應該使用async庫嗎？ 我認為此查詢有更好的方法，不需要循環

Answer 1

如果要獲取與數組條目之一匹配的所有文檔：

const subscriptions = [{
    teacher: 'john',
    student: 'david',
    course: 'math',
  },
  {
    teacher: 'john',
    student: 'david',
    course: 'english',
  },
  {
    teacher: 'matt',
    student: 'max',
    course: 'math',
  },
];

Exam.find({
    $or: subscriptions,
  })
  .then((ret) => {
    // Deal with the data
  })
  .catch((err) => {
    // Deal with the error
  });

---

如果要在分開的數組中獲取數據：

const subscriptions = [{
    teacher: 'john',
    student: 'david',
    course: 'math',
  },
  {
    teacher: 'john',
    student: 'david',
    course: 'english',
  },
  {
    teacher: 'matt',
    student: 'max',
    course: 'math',
  },
];

Promise.all(subscriptions.map(x => Exam.find(x))
  .then(([
    find1,
    find2,
    find3,
  ]) => {
    // Deal with the data
  })
  .catch((err) => {
    // Deal with the error
  });

---

---

// Explaination of :

.then(([
  find1,
  find2,
  find3,
]) => {
  // Deal with the data
})


// This is the equivalent

.then((rets) => {
  const find1 = rets[0];
  const find2 = rets[1];
  const find3 = rets[2];

  // Deal with the data
});

Answer 2

您應該選擇使用or運算符，而不是循環選擇：

Exam.find().or(subscriptions).then(docs => { 
/*logic here*/ 
})
.catch(error => { 
/*error logic here*/ 
})

Answer 3

使用異步

app.get('/',function(req,res){ 
var examsArray= [];

async.each(subscriptions,function(sub,callback){
      Exam.find({teacher:sub.teacher,
                student:sub.student,
                course:sub.course},
             function(err,exams){
                 if(err) return callback(error);
                 if(!err && exams){ 
                     examsArray.push(exams);
                     return callback(exams);
                 }
            });
     },
     , function(err) {
         if (err) { res.json(err); }
         console.log("ALL FINISH");
         if(!err){ res.json(examsArray); }
      });
    });
 });