Group query upon nested object in MongoDB?

For this, use dot notation along with $group in MongoDB. Let us create a collection with documents −

> db.demo617.insertOne(
...    {
...
...       "clientDetails": {
...          "Name": "Chris",
...          "Age":32,
...          "Project":"Online Library Management System"
...       }
...    }
... );
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e99d2b86c954c74be91e69b")
}
>
> db.demo617.insertOne(
...    {
...
...       "clientDetails": {
...          "Name": "David",
...          "Age":34,
...          "Project":"Online Hospital Management System"
...       }
...    }
... );
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e99d2b86c954c74be91e69c")
}
>
> db.demo617.insertOne(
...    {
...
...       "clientDetails": {
...          "Name": "David",
...          "Age":34,
...          "Project":"Online Library Management System"
...       }
...    }
... );
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e99d2b96c954c74be91e69d")
}

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

> db.demo617.find();

This will produce the following output −

{ "_id" : ObjectId("5e99d2b86c954c74be91e69b"), "clientDetails" : { "Name" : "Chris", "Age" : 32, "Project" : "Online Library Management System" } }
{ "_id" : ObjectId("5e99d2b86c954c74be91e69c"), "clientDetails" : { "Name" : "David", "Age" : 34, "Project" : "Online Hospital Management System" } }
{ "_id" : ObjectId("5e99d2b96c954c74be91e69d"), "clientDetails" : { "Name" : "David", "Age" : 34, "Project" : "Online Library Management System" } }

The group query upon nested object in MongoDB −

> db.demo617.aggregate({ $group : {_id : "$clientDetails.Project", All : { $sum : 1 }} });

This will produce the following output −

{ "_id" : "Online Hosiptal Management System", "All" : 1 }
{ "_id" : "Online Library Management System", "All" : 2 }