MongoDB Field Update Operator - $set

Last update on August 19 2022 21:50:43 (UTC/GMT +8 hours)

Description

In MongoDB, the $set operator is used to replace the value of a field to the specified value. If the given field does not exist in the document, the $set operator will add the field to the specified value.

Syntax:

{ $set: { <field1>: <value1>, ... } }

Parameters:

Name	Description
field1	the field which value going to be changed
value1	the new value for the field

Our database name is 'myinfo' and our collection name is "employee". Here, is the collection bellow.

Sample collection "employee"

{
        "_id" : 1,
        "emp_id" : 1231,
        "pinfo" : {
                "empfname" : "Alen",
                "emplname" : "Jones"
        },
        "phno" : "123-123-1234",
        "email" : "[email protected]",
        "sector" : 2,
        "offinfo" : [
                "manager",
                "sales"
        ]
}
{
        "_id" : 2,
        "emp_id" : 1232,
        "pinfo" : {
                "empfname" : "Robart",
                "emplname" : "Bolt"
        },
        "phno" : "123-123-1235",
        "email" : "[email protected]",
        "sector" : 3,
        "offinfo" : [
                "administration",
                "MD"
        ]
}

Example of MongoDB $set operator to update first matching document

If we want to change the content of email field for that employee which id is 1231 the following mongodb statement can be used:

>db.employeeset.update( { emp_id: 1231 },{ $set: {"email": "[email protected]"}});

To see the updated output -

> db.employee.find().pretty();

N.B. find() method displays the documents in a non structured format but to display the results in a formatted way, the pretty() method can be used.

Output of the command

{
        "_id" : 1,
        "email" : "[email protected]",
        "emp_id" : 1231,
        "offinfo" : [
                "manager",
                "sales"
        ],
        "phno" : "123-123-1234",
        "pinfo" : {
                "empfname" : "Alen",
                "emplname" : "Jones"
        },
        "sector" : 2
}
{
        "_id" : 2,
        "emp_id" : 1232,
        "pinfo" : {
                "empfname" : "Robart",
                "emplname" : "Bolt"
        },
        "phno" : "123-123-1235",
        "email" : "[email protected]",
        "sector" : 3,
        "offinfo" : [
                "administration",
                "MD"
        ]
}

Example of MongoDB $set operator to update all matching document

If we want to update the value of "block" with "E" for all those documents which matching the condition sector greater than equal to 2, the following mongodb queries can be used -

>db.employeeset.update( { "sector":{$gte:2} },{ $set: {"block": "E"}},{multi : true});

Here in the above example "multi : true" have used to effect the updates for all the matching document, and the important thing to be noted that, the "block" field does not exists in the document, so, a new field "block" have added with value "E" in the document.

To see the updated output -

> db.employee.find().pretty();

N.B. find() method displays the documents in a non structured format but to display the results in a formatted way, the pretty() method can be used.

Output of the command:

{
        "_id" : 2,
        "block" : "E",
        "email" : "[email protected]",
        "emp_id" : 1232,
        "offinfo" : [
                "administration",
                "MD"
        ],
        "phno" : "123-123-1235",
        "pinfo" : {
                "empfname" : "Robart",
                "emplname" : "Bolt"
        },
        "sector" : 3
}
{
        "_id" : 1,
        "block" : "E",
        "email" : "[email protected]",
        "emp_id" : 1231,
        "offinfo" : [
                "manager",
                "sales"
        ],
        "phno" : "123-123-1234",
        "pinfo" : {
                "empfname" : "Alen",
                "emplname" : "Jones"
        },
        "sector" : 2
}

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