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 } ] }