How can I update child objects in MongoDB database?

To update child objects in MongoDB, use the $set operator with dot notation to target specific fields within nested documents. This allows you to modify individual properties of embedded objects without affecting other fields.

Syntax

db.collection.update(
    { "matchField": "value" },
    { $set: { "parentObject.childField": "newValue" } }
);

Sample Data

Let us first create a collection with documents ?

db.demo21.insertOne({
    "StudentId": "STU-101",
    "StudentDetails": {
        "StudentName": "Chris",
        "StudentAge": 21
    }
});

{
    "acknowledged": true,
    "insertedId": ObjectId("5e14be8922d07d3b95082e6f")
}

Display the document to verify the initial data ?

db.demo21.find().pretty();

{
    "_id": ObjectId("5e14be8922d07d3b95082e6f"),
    "StudentId": "STU-101",
    "StudentDetails": {
        "StudentName": "Chris",
        "StudentAge": 21
    }
}

Example: Update Child Object Field

Update the StudentName field within the nested StudentDetails object ?

db.demo21.update(
    { "StudentId": "STU-101" },
    { $set: { "StudentDetails.StudentName": "Robert" } }
);

WriteResult({ "nMatched": 1, "nUpserted": 0, "nModified": 1 })

Verify Result

Display the updated document ?

db.demo21.find().pretty();

{
    "_id": ObjectId("5e14be8922d07d3b95082e6f"),
    "StudentId": "STU-101",
    "StudentDetails": {
        "StudentName": "Robert",
        "StudentAge": 21
    }
}

Key Points

• Use dot notation with $set to target nested fields: "parent.child"
• Only the specified child field is updated; other fields remain unchanged
• The operation preserves the overall document structure

Conclusion

Use $set with dot notation to update specific fields in child objects. This approach allows precise modifications to nested documents while preserving other embedded fields and the document structure.