Pushing values into array with multi field set to TRUE?

To push values into arrays across multiple documents in MongoDB, use the $push operator with update() and set the multi field to true. This allows updating all matching documents in a single operation.

Syntax

db.collection.update(
    {filter},
    { $push: { arrayField: "value" } },
    { multi: true }
);

Sample Data

db.demo747.insertMany([
    { "CountryName": ["US", "IND"] },
    { "CountryName": ["UK", "US"] },
    { "CountryName": ["UK", "IND"] }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5eae6a50a930c785c834e55f"),
        ObjectId("5eae6a57a930c785c834e560"),
        ObjectId("5eae6a60a930c785c834e561")
    ]
}

Display Documents

db.demo747.find();

{ "_id": ObjectId("5eae6a50a930c785c834e55f"), "CountryName": ["US", "IND"] }
{ "_id": ObjectId("5eae6a57a930c785c834e560"), "CountryName": ["UK", "US"] }
{ "_id": ObjectId("5eae6a60a930c785c834e561"), "CountryName": ["UK", "IND"] }

Example: Push Value to All Documents

Push "AUS" to the CountryName array in all documents ?

db.demo747.update(
    {},
    { $push: { CountryName: "AUS" } },
    { multi: true }
);

WriteResult({ "nMatched": 3, "nUpserted": 0, "nModified": 3 })

Verify Result

db.demo747.find();

{ "_id": ObjectId("5eae6a50a930c785c834e55f"), "CountryName": ["US", "IND", "AUS"] }
{ "_id": ObjectId("5eae6a57a930c785c834e560"), "CountryName": ["UK", "US", "AUS"] }
{ "_id": ObjectId("5eae6a60a930c785c834e561"), "CountryName": ["UK", "IND", "AUS"] }

Key Points

• Empty filter {} matches all documents in the collection.
• multi: true ensures all matching documents are updated, not just the first one.
• $push adds the value to the end of each array.

Conclusion

Use $push with multi: true to add values to arrays across multiple documents efficiently. This approach updates all matching documents in a single operation rather than individual updates.