MongoDB $rename operator

What is the $rename operator in MongoDB?

MongoDB provides a variety of field update operators to update the values of the fields. The $rename operator is one of those operators. The $rename operator is used to change the name of a field. The new name of the field must be different from the old name of the field.

Important points:

The $rename operator performs the $unset operation on both the old and new names before performing the $set operation on the new name.
It can also work with arrays or nested documents.
According to your requirements you can use this operator in findAndModify(), like(), update(), etc.
If the given field does not exist to rename in the document, the $rename operator does nothing.

Syntax of the $rename operator:

Examples:

In the following examples, we are working with:

Database: JavaTpoint
Collection: employees
Document: Six documents that contain the details of the employees

>db.employees.find().pretty()
        {
                "_id" : 1,
                "employee_name" : "Tin",
                "father_name" : "Thor",
                "department" : "Tester",
                "address" : "London",
                "joinning" : 2020,
                "phone_no" : 9856321478,
                "gender" : "Male",
                "age" : 20,
                "salary" : 10000
        }
        {
                "_id" : 2,
                "employee_name" : "John",
                "father_name" : "Mick",
                "department" : "Tester",
                "address" : "NewYork",
                "joining" : 2015,
                "phone_no" : 7896541478,
                "gender" : "Male",
                "age" : 23,
                "salary" : 20000,
                "report_lastDate" : ISODate("2021-08-05T00:00:00Z") 
        }
        {
                "_id" : 3,
                "employee_name" : "Ammy john",
                "father_name" : "John",
                "department" : "Software developer",
                "address" : "London",
                "joining" : 2019,
                "phone_no" : 7985631478,
                "gender" : "Female",
                "age" : 26,
                "salary" : 15000
        }
        {
                "_id" : 4,
                "employee_name" : "Reeza",
                "father_name" : "Reeza Hendricks",
                "department" : "Tester",
                "address" : "USA",
                "joining" : 2020,
                "phone_no" : 7412563278,
                "gender" : "Male",
                "age" : 22,
                "salary" : 20000
        }
        { 
                "_id" : 5,
                "employee_name" : "John Lewis",
                "father_name" : "Lewis",
                "department" : "Software developer",
                "address" : "London",
                "joining" : 2015,
                "phone_no" : 9632587418,
                "gender" : "Male",
                "age" : 25,
                "salary" : 25000,
        }
        {
                "_id" : 6,
                "employee_name" : "Temba",
                "father_name" : "George",
                "department" : "Tester",
                "address" : "NewYork",
                "joining" : 2018,
                "phone_no" : 8965247418,
                "gender" : "Male",
                "age" : 24,
                "salary" : {
                             "first_month" : 15000,
                             "second_month" : 18000,
                             "bonus" : 2000
                           }
        }

Example 1: Renaming a single field

In this example, we're renaming the name of the "joining" field to "joinYear" in the employee's document whose department is Tester.

db.employees.update( {"department": "Tester"},
				{$rename: {"joining": "joinYear"}})

Output:

{
     "_id" : 1,
     "employee_name" : "Tin",
     "father_name" : "Thor",
     "department" : "Tester",
     "address" : "London",
     "joinYear" : 2020,
     "phone_no" : 9856321478,
     "gender" : "Male",
     "age" : 20,
     "salary" : 10000
}
{
     "_id" : 2,
     "employee_name" : "John",
     "father_name" : "Mick",
     "department" : "Tester",
     "address" : "NewYork",
     "joinYear" : 2015,
     "phone_no" : 7896541478,
     "gender" : "Male",
     "age" : 23,
     "salary" : 20000,
     "report_lastDate" : ISODate("2021-08-05T00:00:00Z") 
}
{
     "_id" : 4,
     "employee_name" : "Reeza",
     "father_name" : "Reeza Hendricks",
     "department" : "Tester",
     "address" : "USA",
     "joinYear" : 2020,
     "phone_no" : 7412563278,
     "gender" : "Male",
     "age" : 22,
     "salary" : 20000
}
{
     "_id" : 6,
     "employee_name" : "Temba",
     "father_name" : "George",
     "department" : "Tester",
     "address" : "NewYork",
     "joinYear" : 2018,
     "phone_no" : 8965247418,
     "gender" : "Male",
     "age" : 24,
     "salary" : {
                 "first_month" : 15000,
                 "second_month" : 18000,
                 "bonus" : 2000
                }
}

Example 2: Renaming multiple fields in the documents

In this example, we're renaming the name of the "phone_no" field to "contact_no" in all the documents present in the employees collection.

Output:

{
     "_id" : 1,
     "employee_name" : "Tin",
     "father_name" : "Thor",
     "department" : "Tester",
     "address" : "London",
     "joining" : 2020,
     "contact_no" : 9856321478,
     "gender" : "Male",
     "age" : 20,
     "salary" : 10000
}
{
     "_id" : 2,
     "employee_name" : "John",
     "father_name" : "Mick",
     "department" : "Tester",
     "address" : "NewYork",
     "joining" : 2015,
     "contact_no" : 7896541478,
     "gender" : "Male",
     "age" : 23,
     "salary" : 20000,
     "report_lastDate" : ISODate("2021-08-05T00:00:00Z") 
}
{
     "_id" : 3,
     "employee_name" : "Ammy john",
     "father_name" : "John",
     "department" : "Software developer",
     "address" : "London",
     "joining" : 2019,
     "contact_no" : 7985631478,
     "gender" : "Female",
     "age" : 26,
     "salary" : 15000
}
{
     "_id" : 4,
     "employee_name" : "Reeza",
     "father_name" : "Reeza Hendricks",
     "department" : "Tester",
     "address" : "USA",
     "joining" : 2020,
     "contact_no" : 7412563278,
     "gender" : "Male",
     "age" : 22,
     "salary" : 20000
}
{ 
     "_id" : 5,
     "employee_name" : "John Lewis",
     "father_name" : "Lewis",
     "department" : "Software developer",
     "address" : "London",
     "joining" : 2015,
     "contact_no" : 9632587418,
     "gender" : "Male",
     "age" : 25,
     "salary" : 25000,
}
{
     "_id" : 6,
     "employee_name" : "Temba",
     "father_name" : "George",
     "department" : "Tester",
     "address" : "NewYork",
     "joining" : 2018,
     "contact_no" : 8965247418,
     "gender" : "Male",
     "age" : 24,
     "salary" : {
                 "first_month" : 15000,
                 "second_month" : 18000,
                 "bonus" : 2000
                }
}

Example 3: Renaming a field in nested documents

In this example, we're renaming the name of the "salary.first_month" field to "salary.month" in the employee document whose employee_name is Temba.

db.employee.update({"employee_name": "Temba"},
				{$rename: {"salary.first_month": "salary.month"}})

Output:

{
     "_id" : 6,
     "employee_name" : "Temba",
     "father_name" : "George",
     "department" : "Tester",
     "address" : "NewYork",
     "joining" : 2018,
     "phone_no" : 8965247418,
     "gender" : "Male",
     "age" : 24,
     "salary" : {
                 "month" : 15000,
                 "second_month" : 18000,
                 "bonus" : 2000
                }
}

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