Update values in multiple documents with multi parameter in MongoDB?

To update values in multiple documents in MongoDB, use the multi: true parameter in the update operation. By default, MongoDB updates only the first matching document, but setting multi: true updates all documents that match the query criteria.

Syntax

db.collection.update(
    { query },
    { $set: { field: "newValue" } },
    { multi: true }
);

Sample Data

Let us create a collection with sample documents ?

db.demo390.insertMany([
    { "FirstName": "Chris" },
    { "FirstName": "David" },
    { "FirstName": "Bob" },
    { "FirstName": "Chris" }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e5d1f3a22064be7ab44e7fa"),
        ObjectId("5e5d1f3e22064be7ab44e7fb"),
        ObjectId("5e5d1f4122064be7ab44e7fc"),
        ObjectId("5e5d1f4422064be7ab44e7fd")
    ]
}

Display all documents from the collection ?

db.demo390.find();

{ "_id": ObjectId("5e5d1f3a22064be7ab44e7fa"), "FirstName": "Chris" }
{ "_id": ObjectId("5e5d1f3e22064be7ab44e7fb"), "FirstName": "David" }
{ "_id": ObjectId("5e5d1f4122064be7ab44e7fc"), "FirstName": "Bob" }
{ "_id": ObjectId("5e5d1f4422064be7ab44e7fd"), "FirstName": "Chris" }

Example: Update Multiple Documents

Update all documents where FirstName is "Chris" to "John" using multi: true ?

db.demo390.update(
    { FirstName: "Chris" },
    { $set: { "FirstName": "John" } },
    { multi: true }
);

WriteResult({ "nMatched": 2, "nUpserted": 0, "nModified": 2 })

Verify Result

Display the updated documents ?

db.demo390.find();

{ "_id": ObjectId("5e5d1f3a22064be7ab44e7fa"), "FirstName": "John" }
{ "_id": ObjectId("5e5d1f3e22064be7ab44e7fb"), "FirstName": "David" }
{ "_id": ObjectId("5e5d1f4122064be7ab44e7fc"), "FirstName": "Bob" }
{ "_id": ObjectId("5e5d1f4422064be7ab44e7fd"), "FirstName": "John" }

Key Points

• Without multi: true, only the first matching document gets updated.
• The WriteResult shows nMatched: 2 and nModified: 2, confirming both "Chris" documents were updated.
• Use updateMany() as a modern alternative to update() with multi: true.

Conclusion

The multi: true parameter ensures all matching documents are updated, not just the first one. This is essential for bulk updates across multiple documents in MongoDB collections.