How to add a column in MongoDB collection?

To add a column (field) in MongoDB, you need to update the collection using the $set operator. Since MongoDB is schema-less, adding a new field means updating existing documents to include the new field.

Syntax

db.collection.updateMany({}, {$set: {"newColumnName": "value"}});

Sample Data

Let us create a collection with some sample documents ?

db.addColumnDemo.insertMany([
    {"StudentId": 101, "StudentName": "Chris"},
    {"StudentId": 102, "StudentName": "Robert"},
    {"StudentId": 103, "StudentName": "David"}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e04d66af5e889d7a519950f"),
        ObjectId("5e04d673f5e889d7a5199510"),
        ObjectId("5e04d67bf5e889d7a5199511")
    ]
}

Display the current documents ?

db.addColumnDemo.find().pretty();

{
    "_id": ObjectId("5e04d66af5e889d7a519950f"),
    "StudentId": 101,
    "StudentName": "Chris"
}
{
    "_id": ObjectId("5e04d673f5e889d7a5199510"),
    "StudentId": 102,
    "StudentName": "Robert"
}
{
    "_id": ObjectId("5e04d67bf5e889d7a5199511"),
    "StudentId": 103,
    "StudentName": "David"
}

Example: Adding a New Column

Add a new field StudentCityName to all documents ?

db.addColumnDemo.updateMany({}, {$set: {"StudentCityName": "New York"}});

{
    "acknowledged": true,
    "matchedCount": 3,
    "modifiedCount": 3
}

Verify the result ?

db.addColumnDemo.find().pretty();

{
    "_id": ObjectId("5e04d66af5e889d7a519950f"),
    "StudentId": 101,
    "StudentName": "Chris",
    "StudentCityName": "New York"
}
{
    "_id": ObjectId("5e04d673f5e889d7a5199510"),
    "StudentId": 102,
    "StudentName": "Robert",
    "StudentCityName": "New York"
}
{
    "_id": ObjectId("5e04d67bf5e889d7a5199511"),
    "StudentId": 103,
    "StudentName": "David",
    "StudentCityName": "New York"
}

Key Points

• Use updateMany() with an empty filter {} to update all documents
• The $set operator adds new fields or updates existing ones
• New fields are added instantly without affecting the collection schema

Conclusion

Adding columns in MongoDB is accomplished using updateMany() with the $set operator. This flexible approach allows you to add new fields to existing documents without schema modifications.