Data not getting fetched using aggregation query in nodejs - node.js

Question

I tried below code but only first match is checked and displayed,others displayed as object, why I am unable to see it in console. I have 3 collections student subject teacher, also made schema for the same. tried aggregation
Student.aggregate([
{
$match: { name: 'abcd'}
},
{
$lookup:
{
from:'teachers',
pipeline: [{ $match: { name: 'pqrs' } },],
as: "teacherLookup"
}
},
{
$lookup:
{
from:'subjects',
pipeline: [{ $match: { name: 'computer' } }],
as: "subjectLookup"
}
}
]).then(function (res) {
console.log(res);
res.forEach(function(students){
let id = students._id;
console.log(id+ ' got id ')
}
output
student
name:'abcd' -- its fetched and other two not displaying values only shows object
teacherLookup: [ [Object] ]
subjectLookup: [ [Object] ]

Answer 1

You were there just to project something you have to use $project stage.
Here I'm adding the query:
Student.aggregate([
{
$match: { name: 'abcd'}
},
{
$lookup:{
from:'teachers',
pipeline: [
{
$match: { name: 'pqrs' }
},
{
$project:{
"_id":1
}
}
],
as: "teacherLookup"
}
},
{
$lookup:
{
from:'subjects',
pipeline: [
{
$match: { name: 'computer' }
},
{
$project:{
"_id":1
}
}
],
as: "subjectLookup"
}
}
])
For more about $project refer here.
Hope this will help :)