“Structured” grouping query in MongoDB to display result with a new field displaying the count

For this, use $group in MongoDB IN aggregate(). The $group groups input documents by the specified _id expression and for each distinct grouping, outputs a document. Let us first create a collection with documents −

> db.demo534.insertOne({_id:10,"ProductId":100,"ProductName":"Product-1"});
{ "acknowledged" : true, "insertedId" : 10 }
> db.demo534.insertOne({_id:11,"ProductId":100,"ProductName":"Product-2"});
{ "acknowledged" : true, "insertedId" : 11 }
> db.demo534.insertOne({_id:12,"ProductId":101,"ProductName":"Product-1"});
{ "acknowledged" : true, "insertedId" : 12 }

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

> db.demo534.find();

This will produce the following output −

{ "_id" : 10, "ProductId" : 100, "ProductName" : "Product-1" }
{ "_id" : 11, "ProductId" : 100, "ProductName" : "Product-2" }
{ "_id" : 12, "ProductId" : 101, "ProductName" : "Product-1" }

Following is the query to implement structured grouping query in MongoDB −

> db.demo534.aggregate(
... {
...    $group:
...    {
...       _id:
...          {
...             productName: "$ProductName",
...             productId: "$ProductId"
...          },
...          count:
...             {
...                $sum: 1
...             }
...          },
...       },
...       {
...          $group:
...             {
...                _id: "$_id.productId",
...                itemCounts:
...                   {
...                      "$push":
...                         {
...                            productName: "$_id.productName",
...                            count: "$count"
...                   }
...             }
...       }
... })

This will produce the following output −

{ "_id" : 101, "itemCounts" : [ { "productName" : "Product-1", "count" : 1 } ] }
{ "_id" : 100, "itemCounts" : [ { "productName" : "Product-2", "count" : 1 }, { "productName" : "Product-1", "count" : 1 } ] }