Getting items that referenced an object id - node.js

Question

// PRODUCT MODEL
const productSchema = new mongoose.Schema(
{
category: {
type: mongoose.Schema.Types.ObjectId,
ref: "Category",
},
name: {
type: String,
required: true,
},
price: {
type: Number,
required: true,
default: 0,
},
colors: [
{
type: mongoose.Schema.Types.ObjectId,
ref: "Color",
},
],
sizes: {
type: Array,
default: [
{ id: 1, size: "XS" },
{ id: 2, size: "S" },
{ id: 3, size: "M" },
{ id: 4, size: "L" },
{ id: 5, size: "XL" },
{ id: 6, size: "XXL" },
],
},
},
{ timestamps: true }
);
const Product = mongoose.model("Product", productSchema);
export default Product;
// CATEGORY MODEL
const CategorySchema = new mongoose.Schema(
{
name: String,
},
{ timestamps: true, toJSON: true, toObject: true }
);
CategorySchema.virtual("items").get(async function () {
return await CategorySchema.aggregate([
{
$lookup: {
from: "Product",
localField: "category",
foreignField: "_id",
as: "items",
},
},
]);
});
const Category = mongoose.model("Category", CategorySchema);
export default Category;
Hello, please i'm trying to get list of items that referenced each categoryid on the product model, i want to add the result as a virtual field called "count" from the category model and not the product model. i'm getting this error "TypeError: Cannot use 'in' operator to search for 'transform' in true".
i want to get the result the way it was done in this example from mongodb doc about inventory and orders but i'm getting "items: {}". docs.mongodb.com/manual/reference/operator/aggregation/lookup

Answer 1

router.get(
"/counts",
catchAsync(async (req, res) => {
const stats = await Category.aggregate([
{
$lookup: {
from: "products",
localField: "_id",
foreignField: "category",
as: "count",
},
},
{
$project: {
name: 1,
image: 1,
count: {
$cond: {
if: { $isArray: "$count" },
then: { $size: "$count" },
else: "NA",
},
},
},
},
]);
if (!stats) {
return res.status(404).json("No data found");
}
res.status(200).json(stats);
})
);
For anyone that is trying to achieve the result i wanted, i used Category.aggregate on the category route instead of creating a virtual field from the category model.