Appending an entry in one to many embedded documents with MongoDB

To append an entry in MongoDB one-to-many embedded documents, use the $push operator which adds new elements to an existing array field without affecting other array elements.

Syntax

db.collection.update(
    { "matchField": "value" },
    { $push: { "arrayField": newDocument } }
);

Create Sample Data

Let us create a collection with documents ?

db.demo253.insertOne({
    _id: "101",
    isActive: false,
    details: [
        {
            Name: "Chris"
        },
        {
            CountryName: "US"
        }
    ]
});

{ "acknowledged": true, "insertedId": "101" }

Display all documents from the collection ?

db.demo253.find();

{ "_id": "101", "isActive": false, "details": [ { "Name": "Chris" }, { "CountryName": "US" } ] }

Example: Append Entry to Embedded Array

Following is the query to append an entry in one to many embedded documents ?

db.demo253.update(
    { _id: "101" }, 
    { $push: { details: { Age: 21 } } }
);

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

Verify Result

Display all documents to see the appended entry ?

db.demo253.find();

{ "_id": "101", "isActive": false, "details": [ { "Name": "Chris" }, { "CountryName": "US" }, { "Age": 21 } ] }

Conclusion

The $push operator effectively appends new documents to embedded arrays in MongoDB. It preserves existing array elements while adding new entries at the end, making it ideal for one-to-many relationships.