how can I get value in populate() in mongoose? - node.js

Question

I want to return one index's object of the array,
but when I query, It returns to me that all of the documents.
This is my Schema(userTb)
const userTbSchema = new Schema({
_id: mongoose.Schema.Types.ObjectId,
userId: String,
gender: String
}
And this is my another Schema(product)
const productSchema = new Schema({
_id: mongoose.Schema.Types.ObjectId,
product: String,
userTbId: { type: mongoose.Schema.Types.ObjectId, ref: "userTb", required: true },
}
And They are in another js file.
This is the result of the query of my Schema(product) don't use Populate.
{
"_id": "5fc4c13f32ab3174acb01234",
"product": "watch",
"userTbId": "5fc4c13f32ab3174acb08540"
},
{
"_id": "5fc4c2d6b3a2a054d4dc1235",
"userId": "car",
"userTbId": "5fc4c2d6b3a2a054d4dc462c"
}
And This is the result of the query of my Schema(product) when I using Populate.
{
"_id": "5fc4c13f32ab3174acb01234",
"product": "watch",
"userTbId": {
"_id": "5fc4c13f32ab3174acb08540",
"userId": "go05111",
"gender": "male"
}
},
{
"_id": "5fc4c2d6b3a2a054d4dc1235",
"userId": "car",
"userTbId": {
"_id": "5fc4c2d6b3a2a054d4dc462c",
"userId": "Chips",
"gender": "female"
}
}
I want to get the only { "gender" : "male" } object in proudct, like...
{
"_id": "5fc4c13f32ab3174acb01234",
"product": "watch",
"userTbId": {
"_id": "5fc4c13f32ab3174acb08540",
"userId": "go05111",
"gender": "male"
}
}
so I query like this
router.get('/:gender', (req, res, next) => {
Product.find({
"userTbId.gender": req.params.gender
})
.populate({
path: 'userTbId',
match: {
userId: req.params.userId
}
})
.exec()
.then(docs => {
res.status(200).json({
docs
});
})
.catch(err => {
res.status(500).json({
error: err
});
});
});
but the result is nothing returned.
I think the userTbId is ObjectId, so even if populate() is used, the value does not appear when find() is used.
I tried a few different ways, but it didn't work that I want.
how can I fix it in mongoose?
would you please help me?

Answer 1

In mongoose, populate will execute on the result set from the find query.
In your Product schema userTbId is an object id and it will not have the gender property unless it gets populated. To achieve your goal only by using mongoose, you can write a query like below. First you need to find all the userTbIds for your gender and userId. Then query your Product schema for the returned userTbIds. Corrections and optimisations are welcome.
router.get('/:gender', (req, res, next) => {
userTbId.find({
"gender": req.params.gender,
"userId": req.params.userId
}).exec()
.then(docs => {
let ids = docs.map(doc => doc.id);
Product.find({
"userTbId": {$in:ids}
})
.populate({
path: 'userTbId'
})
.exec()
.then(docs => {
res.status(200).json({
docs
});
})
.catch(err => {
res.status(500).json({
error: err
});
});
})
.catch(err => {
res.status(500).json({
error: err
});
});
});