$group Group Operation in Mongo

Grouping the Employee using $group operator under Employee_Detail collection.

Example:

[
{ 
    "_id" : ObjectId("60179dd62381fc69d5f1c5a0"), 
    "Emp_Name" : "Jatin", 
    "Emp_Age" : NumberInt(24), 
    "Emp_Salary" : NumberInt(34000), 
    "Emp_Grade" : "C", 
    "Emp_Joining_Date" : ISODate("2020-07-03T18:30:00.000+0000")
}
{ 
    "_id" : ObjectId("60179dd62381fc69d5f1c5a1"), 
    "Emp_Name" : "Terens", 
    "Emp_Age" : NumberInt(27), 
    "Emp_Salary" : NumberInt(34000), 
    "Emp_Grade" : "D", 
    "Emp_Joining_Date" : ISODate("2020-07-03T18:30:00.000+0000")
}
{ 
    "_id" : ObjectId("60179dd62381fc69d5f1c5a2"), 
    "Emp_Name" : "Manu", 
    "Emp_Age" : NumberInt(21), 
    "Emp_Salary" : NumberInt(34000), 
    "Emp_Grade" : "A", 
    "Emp_Joining_Date" : ISODate("2020-07-03T18:30:00.000+0000")
}
{ 
    "_id" : ObjectId("60179dd62381fc69d5f1c5a3"), 
    "Emp_Name" : "Sagun", 
    "Emp_Age" : NumberInt(20), 
    "Emp_Salary" : NumberInt(34000), 
    "Emp_Grade" : "B", 
    "Emp_Joining_Date" : ISODate("2020-07-03T18:30:00.000+0000")
}
{ 
    "_id" : ObjectId("60179dd62381fc69d5f1c5a4"), 
    "Emp_Name" : "Pankaj", 
    "Emp_Age" : NumberInt(60), 
    "Emp_Salary" : NumberInt(34000), 
    "Emp_Grade" : "D", 
    "Emp_Joining_Date" : ISODate("2020-07-03T18:30:00.000+0000")
}
]

Approach

Query: To group employee based on one field. 

db.Employee_Detail.aggregate([
    {"$group":{"_id":"$Emp_Grade","gradeWiseEmp":{"$push":{"Emp_Name":"$Emp_Name"}}}}
    ]);

Output: 

[
    {
        "_id": "D",
        "gradeWiseEmp": [
            {
                "Emp_Name": "Terens"
            },
            {
                "Emp_Name": "Pankaj"
            }
        ]
    },
    {
        "_id": "B",
        "gradeWiseEmp": [
            {
                "Emp_Name": "Sagun"
            }
        ]
    },
    {
        "_id": "C",
        "gradeWiseEmp": [
            {
                "Emp_Name": "Jatin"
            }
        ]
    },
    {
        "_id": "A",
        "gradeWiseEmp": [
            {
                "Emp_Name": "Manu"
            }
        ]
    }
]