Updating an array with $push in MongoDB

To update an array with $push in MongoDB, use the updateOne() method. The $push operator adds elements to an array field, and when combined with the positional operator $, it can target specific array elements.

Syntax

db.collection.updateOne(
    { "arrayField": { "$elemMatch": { "field": "value" } } },
    { "$push": { "arrayField.$.targetField": newElement } }
);

Sample Data

Let us create a collection with documents ?

db.demo526.insertOne({
    "CountryName": "US",
    "TeacherName": "Bob",
    "StudentInformation": [
        {
            "Name": "Chris",
            "Subject": "MySQL",
            "ListOfMailId": []
        },
        {
            "Name": "David",
            "Subject": "MongoDB",
            "ListOfMailId": []
        }
    ]
});

{
    "acknowledged": true,
    "insertedId": ObjectId("5e8af031437efc8605595b6b")
}

Display all documents from the collection ?

db.demo526.find();

{
    "_id": ObjectId("5e8af031437efc8605595b6b"),
    "CountryName": "US",
    "TeacherName": "Bob",
    "StudentInformation": [
        { "Name": "Chris", "Subject": "MySQL", "ListOfMailId": [] },
        { "Name": "David", "Subject": "MongoDB", "ListOfMailId": [] }
    ]
}

Example: Update Array with $push

Following is the query to update an array with $push ?

db.demo526.updateOne(
    {
        _id: ObjectId("5e8af031437efc8605595b6b"),
        "StudentInformation": { "$elemMatch": { "Name": "David", "Subject": "MongoDB" }}
    },
    {
        "$push": { "StudentInformation.$.ListOfMailId": { "MailId": "David@gmail.com" }}
    }
);

{ "acknowledged": true, "matchedCount": 1, "modifiedCount": 1 }

Verify Result

Display the updated document ?

db.demo526.find();

{
    "_id": ObjectId("5e8af031437efc8605595b6b"),
    "CountryName": "US",
    "TeacherName": "Bob",
    "StudentInformation": [
        { "Name": "Chris", "Subject": "MySQL", "ListOfMailId": [] },
        { "Name": "David", "Subject": "MongoDB", "ListOfMailId": [{ "MailId": "David@gmail.com" }] }
    ]
}

Conclusion

The $push operator effectively adds elements to arrays in MongoDB. Combined with $elemMatch and the positional operator $, it enables precise updates to nested array elements within documents.