search queries in nodejs and mongodb and populated data - node.js

Question

i have a web app that's written in nodejs and mongodb, i have the following two models
var TeacherSchema = new Schema({
school_id:[{type: Schema.Types.ObjectId, ref: 'School'}],
name: String,
subjects: [{type: Schema.Types.ObjectId, ref: 'Subject'}],
});
var SubjectSchema = new Schema({
title : String,
school_id:[{type: Schema.Types.ObjectId, ref: 'School'}]
});
i wrote an api that searches throw the teacher or subjects
router.get("/field-teacher-subject", function (req, res) {
var school_id= req.query.schoolId;
Subject.find(school_id:'school_id,function (err, subjects) {
if (err) {
console.log(err);
res.json({status: "error", message: err.message});
} else {
var sub_array=[];
for(var q in subjects){
sub_array.push(subjects[q]._id);
}
Teacher.find({subjects:{$in :sub_array }},{first_name:true, father_name:true, last_name : true, subjects:true}).populate('subjects')
.exec(function(tech) {
console.log("hello: ");
var subjeto = [];
if(tech){
for(var p in tech){
subjeto.push(tech[p].subjects);
}
}
res.json({status: "success", message: "subjects returned",
items: tech});
}).catch(function(err){
if(err){
res.json({status:"error",
message:"error occurred"+err.message});
return;
}
});
}
}).limit(parseInt(req.query.max));
});
THIS RETURNS null when i search for a name,
what is the best way to solve this

Answer 1

Hard to know what you are asking but your code has few errors. Let's clean up your code, shall we?
router.get("/field-teacher-subject", function (req, res) {
// get subjects
Subject
.find({ school_id: req.query.schoolId }) // 1st argument is an object
.limit(parseInt(req.query.max)) // should go before
.exec(function (err, subjects) { // use .exec()
if (err) {
console.log(err);
return res.json({ status: "error", message: err.message });
}
// get subject IDs
var sub_array = subjects.map(function (subject) { return subject._id; });
// get teachers assigned to subjects
Teacher
.find({ subjects: { $in: sub_array }})
.select('first_name father_name last_name subjects')
.populate('subjects')
.exec(function(err, teachers) { // 1st argument is an error
if (err) {
console.log(err);
return res.json({status: "error", message: err.message });
}
var subjeto = teachers.map(function (teacher) { return teacher.subjects; });
res.json({status: "success", message: "subjects returned", items: teachers });
});
});
});
Useful links:
See 3rd example in doc on how to use .limit() and .exec().
.map()
You tried to use .exec() like .then() and .catch() in your second query