Count by category and sum it up in MongoDB - node.js

Question

I have a product collection in MongoDb which sole fields like _id, category, user_id.
I want to check and count the sum number of each category in collection given the matching the user_id and then sum up all the count again at the end.
my solution is :
return Product.aggregate([
{ $match: { "user_id": "id if user that added the product" } },
{ "$unwind": "$category" },
{
"$group": {
"_id": {
'category': '$category',
},
"count": { "$sum": 1 }
}
},
{ "$sort": { "_id.category": 1 } },
{
"$group": {
"_id": "$_id.category",
"count": { "$first": "$count" }
}
}
])
the code gives me the count of each category without matching the condition of user_id. But when I add the $match it fails.
Product Schema:
const ProductSchema = new Schema({
title: {
type: String,
required: true
},
description: {
type: String,
required: true
},
quantity: {
type: Number,
default: -1
},
category:
{
type: String,
required: true
},
manufactured_by: {
type: String,
required: true
},
user_id: {
type: Schema.Types.ObjectId,
ref: 'user',
required: true
}
})
my result if I dont add the condition:
[
{
"_id": "A Tables",
"count": 1
},
{
"_id": "C Tables",
"count": 4
},
{
"_id": "B Tables",
"count": 2
}
]

Answer 1

Not sure what you are trying to achieve from the last stage in your pipeline.
But the following should give you desired output (without any complications that you added)
async getSellerStatistics(seller_id) {
return await Product.aggregate([
{ $match: { user_id: seller_id } }
{ $unwind: "$category" },
{
$group: {
_id: "$category",
count: { $sum: 1 },
},
},
{ $sort: { _id: 1 } },
])
}