How to re-map the fields of a MongoDB collection?

To re-map the fields of a MongoDB collection, use $rename operator with update() or updateMany(). This operator allows you to rename field names across documents in your collection.

Syntax

db.collection.updateMany(
    {},
    { $rename: { "oldFieldName": "newFieldName" } }
);

Sample Data

Let us create a collection with sample documents ?

db.demo171.insertMany([
    {
        "Name": "Chris",
        "Details": {
            "SubjectName": "MySQL",
            "CountryName": "US"
        }
    },
    {
        "Name": "John",
        "Details": {
            "SubjectName": "MongoDB",
            "CountryName": "UK"
        }
    }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e3837399e4f06af551997e0"),
        ObjectId("5e3837399e4f06af551997e1")
    ]
}

Display all documents from the collection ?

db.demo171.find().pretty();

{
    "_id": ObjectId("5e3837399e4f06af551997e0"),
    "Name": "Chris",
    "Details": {
        "SubjectName": "MySQL",
        "CountryName": "US"
    }
}
{
    "_id": ObjectId("5e3837399e4f06af551997e1"),
    "Name": "John",
    "Details": {
        "SubjectName": "MongoDB",
        "CountryName": "UK"
    }
}

Example: Rename Top-Level Field

Rename the "Name" field to "StudentName" across all documents ?

db.demo171.updateMany(
    {},
    { $rename: { "Name": "StudentName" } }
);

{
    "acknowledged": true,
    "matchedCount": 2,
    "modifiedCount": 2
}

Verify Result

db.demo171.find().pretty();

{
    "_id": ObjectId("5e3837399e4f06af551997e0"),
    "Details": {
        "SubjectName": "MySQL",
        "CountryName": "US"
    },
    "StudentName": "Chris"
}
{
    "_id": ObjectId("5e3837399e4f06af551997e1"),
    "Details": {
        "SubjectName": "MongoDB",
        "CountryName": "UK"
    },
    "StudentName": "John"
}

Example: Rename Nested Field

Rename nested field "SubjectName" to "Subject" ?

db.demo171.updateMany(
    {},
    { $rename: { "Details.SubjectName": "Details.Subject" } }
);

{
    "acknowledged": true,
    "matchedCount": 2,
    "modifiedCount": 2
}

Key Points

• Use {} as filter to rename fields across all documents in the collection.
• For nested fields, use dot notation like "parent.child".
• updateMany() is preferred over the legacy update() method.
• If the old field doesn't exist, the operation is ignored for that document.

Conclusion

The $rename operator provides an efficient way to restructure your MongoDB collections by changing field names. Use updateMany() with an empty filter to rename fields across all documents in the collection.