Using MongoDB nested $group and $sum to get the count of stocks with similar ProductID?

The $group in MongoDB is used to group input documents by the specified _id expression. Let us create a collection with documents −

> db.demo466.insertOne(
... {
...
... "ProductPrice" :150,
... "ProductQuantity" : 1,
... "ProductName" : "Product-1",
... "ActualAmount" :110,
... "ProductProfit" : 40,
... "ProductId" : 1
... }
... );
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e80477cb0f3fa88e2279066")
}
>
> db.demo466.insertOne(
... {
...
... "ProductPrice" :150,
... "ProductQuantity" : 1,
... "ProductName" : "Product-1",
... "ActualAmount" :110,
... "ProductProfit" : 40,
... "ProductId" : 2
... }
... );
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e80477db0f3fa88e2279067")
}
> db.demo466.insertOne(
... {
...
... "ProductPrice" :170,
... "ProductQuantity" : 2,
... "ProductName" : "Product-2",
... "ActualAmount" :130,
... "ProductProfit" : 50,
... "ProductId" : 3
... }
... );
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e80477eb0f3fa88e2279068")
}

Display all documents from a collection with the help of find() method −

> db.demo466.find();

This will produce the following output −

{ "_id" : ObjectId("5e80477cb0f3fa88e2279066"), "ProductPrice" : 150, "ProductQuantity" : 1,
"ProductName" : "Product-1", "ActualAmount" : 110, "ProductProfit" : 40, "ProductId" : 1 }
{ "_id" : ObjectId("5e80477db0f3fa88e2279067"), "ProductPrice" : 150, "ProductQuantity" : 1,
"ProductName" : "Product-1", "ActualAmount" : 110, "ProductProfit" : 40, "ProductId" : 2 }
{ "_id" : ObjectId("5e80477eb0f3fa88e2279068"), "ProductPrice" : 170, "ProductQuantity" : 2,
"ProductName" : "Product-2", "ActualAmount" : 130, "ProductProfit" : 50, "ProductId" : 3 }

Following is the query to use nested $group and $sum in MongoDB −

> db.demo466.aggregate([
... {
...    '$group': {
...       '_id': {
...          'ProductName': '$ProductName',
...       },
...       'ActualAmount': {'$sum': '$ActualAmount'},
...       'ProductQuantity': {'$sum': '$ProductQuantity'},
...       'ProductId': {'$addToSet': '$ProductId'},
...    },
... },
... {
...    '$project': {
...       'ProductQuantity': true,
...       'ActualAmount': true,
...       'NumberOfProductInStock': {'$size': '$ProductId'}
...    }
... }])

This will produce the following output −

{ "_id" : { "ProductName" : "Product-2" }, "ActualAmount" : 130, "ProductQuantity" : 2,
"NumberOfProductInStock" : 1 }
{ "_id" : { "ProductName" : "Product-1" }, "ActualAmount" : 220, "ProductQuantity" : 2,
"NumberOfProductInStock" : 2 }