find nested (embedded) object in the collection - node.js

Question

while i was going through my problem on StackOverflow,i noticed same question was asked before aswell,but none of them had got a good response,or an actual answer.
Mongoose Find One on Nested Object
How can I find nested objects in a document?
well back to my question: i wanted to find the object that is nested in the schema. trying findMany gives all the objects,and findOne give just the first one,but i want particular objects whose id i pass through req.body.checkbox.
my JS code goes like..
app.post("/data", uploads, function (req, res) {
User.findById(req.user.id, function (err, foundUser) {
if (err) {
console.log(err);
} else {
if (foundUser) {
var checkedBox = req.body.checkbox;
console.log(checkedBox);
User.findMany({_id:foundUser._id},{comments:{$elemMatch:{_id:checkedBox}}} ,function(err,checkedobj){
if(err){
console.log(err);
}
else{
console.log(checkedobj.comments);
if (Array.isArray(checkedobj.comments)) {
res.render("checkout",{SIMG: checkedobj.comments});
} else {
res.render("checkout",{SIMG: [checkedobj.comments]});
}
}
})
}
}
});
});
here is my schema,for reference
const commentSchema = new mongoose.Schema({
comment: String,
imagename: String,
permission:{type:Number,default:0},
});
const Comment = new mongoose.model("Comment", commentSchema);
const userSchema = new mongoose.Schema({
firstname: String,
lastname: String,
email: String,
password: String,
comments: [commentSchema],
permission:{type:Number,default:0},
});
userSchema.plugin(passportLocalMongoose);
const User = new mongoose.model("User", userSchema);
example
{
"_id" : ObjectId("5ec3f54adfaa1560c0f97cbf"),
"firstname" : "q",
"lastname" : "q",
"username" : "q#q.com",
"salt" : "***",
"hash" : "***",
"__v" : NumberInt(2),
"comments" : [
{
"permission" : NumberInt(0),
"_id" : ObjectId("5ec511e54db483837885793f"),
"comment" : "hi",
"imagename" : "image-1589973477170.PNG"
}
],
"permission" : NumberInt(1)
}
also when i check 3 checkboxes, console.log(checkBox) logs:
[
'5ec543d351e2db83481e878e',
'5ec589369d3e9b606446b776',
'5ec6463c4df40f79e8f1783b'
]
but console.log(checkedobj.comments) gives only one object.
[
{
permission: 0,
_id: 5ec543d351e2db83481e878e,
comment: 'q',
imagename: 'image-1589986259358.jpeg'
}
]

Answer 1

When you want multiple matching elements from an array you should use $filter aggregation operator
And as a precaution, first check req.body.checkbox is an array or not and convert it into an array of ObjectIds
app.post("/data", uploads, function (req, res) {
var ObjectId = mongoose.Types.ObjectId;
User.findById(req.user.id, function (err, foundUser) {
if (err) {
console.log(err);
} else {
if (foundUser) {
var checkedBox = req.body.checkbox;
if (!Array.isArray(checkedBox)) {
checkedBox = [checkedBox]
}
console.log(checkedBox);
var checkedBoxArray = checkedBox.map(id => ObjectId(id))
User.aggregate([
{$match: {_id: foundUser._id}},
{
$project: {
comments: {
$filter: {
input: "$comments",
as: "comment",
cond: { $in: [ "$$comment._id", checkedBoxArray ] }
}
}
}
}
],function(err,checkedobj){
if(err){
console.log(err);
}
else{
console.log(checkedobj[0].comments);
if (Array.isArray(checkedobj[0].comments)) {
res.render("checkout",{SIMG: checkedobj[0].comments});
} else {
res.render("checkout",{SIMG: [checkedobj[0].comments]});
}
}
})
}
}
});
});
Working example - https://mongoplayground.net/p/HnfrB6e4E3C
Above example will return only 2 comments matching the ids

Answer 2

You can make use of findById() method, more documentation about it is provided here
You can use something like this to search by object id:-
var id = "123";
userSchema.findById(id, function (err, user) { ... } );
Hope this helps!