Mongoose - How to populate a sub document on condition - node.js

Question

I'm new to Mongoose I don't know how to populate on condition.
So this is my model :
const OrderSchema = new Schema({
products: [{ type: Schema.Types.ObjectId, ref: 'Product' }],
remarks: {type: String, lowercase: true}
});
mongoose.model("Order", OrderSchema);
const ProductSchema = new Schema({
reference: {type: String}
status: {type: Schema.Types.ObjectId, ref: 'ProductStatus'}
});
mongoose.model("Product", ProductSchema);
const ProductStatus = new Schema({
name: {type: String}
});
const CountrySchema = new Schema({
name: {type: String}
});
mongoose.model("Country", CountrySchema);
I have a getOrderById methods
export const getOrderById = async (req, res) => {
let id = req.params.id;
try {
await orderModel
.findById(id)
.populate({
path: 'products',
populate: {
path: 'country',
model: 'Country'
}
})
.populate({
path: 'products',
populate: {
path: 'status',
model: 'ProductStatus'
}
})
.exec(function (err, orders) {
if (err) {
res.send(err);
}
res.status(200).json(orders);
});
} catch (error) {
console.log(error);
}
}
And now I would like to show in the order lists all products that have the status Received in France.

Answer 1

First, I guess you also missed reference to the country in the product schema, so assuming these are your corrected schemas:
const OrderSchema = new Schema({
products: [{
type: Schema.Types.ObjectId,
ref: 'Product'
}],
remarks: {
type: String,
lowercase: true
}
});
const Order = mongoose.model("Order", OrderSchema);
const ProductSchema = new Schema({
reference: {
type: String
},
country: {
type: Schema.Types.ObjectId,
ref: 'Country'
},
status: {
type: Schema.Types.ObjectId,
ref: 'ProductStatus'
}
});
const Product = mongoose.model("Product", ProductSchema);
const ProductStatusSchema = new Schema({
name: {
type: String
}
});
const ProductStatus = mongoose.model("ProductStatus", ProductStatusSchema);
const CountrySchema = new Schema({
name: {
type: String
}
});
const Country = mongoose.model("Country", CountrySchema);
As far as I understand you want to only show the products, whose country's name is 'France' and ProductStatus' name is 'Received', these kind of operations are done through Aggregation
Your query may look like this assuming you want to do it one query:
const getOrderById = async (req, res) => {
let id = req.params.id.toString();
const ObjectId = mongoose.Types.ObjectId
try {
const aggregationStages = [{
$match: {
_id: ObjectId(id) //It is important to cast to ObjectId in aggregations
}
}, {
$lookup: {
from: 'products',
let: {
productIds: '$products'
},
pipeline: [{
$match: {
$expr: {
$in: ['$_id', '$$productIds']
}
}
}, {
$lookup: {
from: 'countries',
localField: 'country',
foreignField: '_id',
as: 'country'
}
}, {
$lookup: {
from: 'productstatuses',
localField: 'status',
foreignField: '_id',
as: 'status'
}
}, {
$match: {
'country.name': 'France',
'status.name': 'Received'
}
}],
as: 'products'
}
}];
await orderModel.aggregate(aggregationStages)
.exec(function (err, orders) { // The return is an array btw.
if (err) {
res.send(err);
}
res.status(200).json(orders);
});
} catch (error) {
console.log(error);
}
}
If you feel the aggregation is complicated you may resort to breaking it to smaller simpler queries. Feel free to ask if you need more explanation/modification.