MongoDB query to update array object in index N?

To update an array object at a specific index in MongoDB, use the $ positional operator with dot notation. The $ operator identifies the matched array element, allowing you to update its nested fields.

Syntax

db.collection.update(
    {"arrayField.matchingField": "value"},
    {$set: {"arrayField.$.nestedField": "newValue"}}
)

Sample Data

db.demo489.insertOne({
    details: [
        {
            id: 101,
            "Info1": {
                "StudentName": "Chris"
            },
            "Info2": {
                "TeacherName": "David"
            }
        },
        {
            id: 102,
            "Info1": {
                "StudentName": "Carol"
            },
            "Info2": {
                "TeacherName": "Mike"
            }
        }
    ]
})

{
    "acknowledged": true,
    "insertedId": ObjectId("5e8356e0b0f3fa88e22790ba")
}

Display all documents from the collection ?

db.demo489.find()

{
    "_id": ObjectId("5e8356e0b0f3fa88e22790ba"),
    "details": [
        {
            "id": 101,
            "Info1": {"StudentName": "Chris"},
            "Info2": {"TeacherName": "David"}
        },
        {
            "id": 102,
            "Info1": {"StudentName": "Carol"},
            "Info2": {"TeacherName": "Mike"}
        }
    ]
}

Example: Update Array Object by Matching Field

Update the array object where id is 102 ?

db.demo489.update(
    {"details.id": 102},
    {
        $set: {
            "details.$.Info1.StudentName": "Robert",
            "details.$.Info2.TeacherName": "John",
            "details.$.CountryName": "US"
        }
    }
)

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

Verify Result

db.demo489.find().pretty()

{
    "_id": ObjectId("5e8356e0b0f3fa88e22790ba"),
    "details": [
        {
            "id": 101,
            "Info1": {
                "StudentName": "Chris"
            },
            "Info2": {
                "TeacherName": "David"
            }
        },
        {
            "id": 102,
            "Info1": {
                "StudentName": "Robert"
            },
            "Info2": {
                "TeacherName": "John"
            },
            "CountryName": "US"
        }
    ]
}

Key Points

• The $ operator matches the first array element that satisfies the query condition
• Use dot notation to access nested fields within the matched array element
• Multiple fields can be updated in a single operation using $set

Conclusion

The positional operator $ combined with dot notation provides an efficient way to update specific array objects in MongoDB. This approach allows precise modifications to nested document fields within arrays.