Update a single list item of a MongoDB document?

To update a single list item in MongoDB, use the positional operator ($) to target the first array element that matches your query condition. This operator allows you to update specific fields within array elements without affecting other items in the list.

Syntax

db.collection.update(
    { "arrayField.field": "matchValue" },
    { $set: { "arrayField.$.field": "newValue" } }
);

Sample Data

Let us first create a collection with documents ?

db.updateASingleListDemo.insertOne({
    _id: 1,
    "EmployeeName": "Chris",
    "EmployeeDetails": [
        {
            "EmployeeId": "EMP-101",
            "EmployeeSalary": 18999
        }
    ]
});

{ "acknowledged": true, "insertedId": 1 }

Display all documents from the collection ?

db.updateASingleListDemo.find().pretty();

{
    "_id": 1,
    "EmployeeName": "Chris",
    "EmployeeDetails": [
        {
            "EmployeeId": "EMP-101",
            "EmployeeSalary": 18999
        }
    ]
}

Example: Update Single List Item

Update the salary of employee with ID "EMP-101" by incrementing it by 1 ?

db.updateASingleListDemo.update(
    { _id: 1, 'EmployeeDetails.EmployeeId': "EMP-101" },
    { $inc: { 'EmployeeDetails.$.EmployeeSalary': 1 } }
);

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

Verify Result

Check the updated document ?

db.updateASingleListDemo.find().pretty();

{
    "_id": 1,
    "EmployeeName": "Chris",
    "EmployeeDetails": [
        {
            "EmployeeId": "EMP-101",
            "EmployeeSalary": 19000
        }
    ]
}

Key Points

• The $ positional operator matches the first array element that satisfies the query condition.
• Use dot notation to specify the field within the array element to update.
• The query condition must include a field from the array to identify which element to update.

Conclusion

The positional operator $ provides an efficient way to update specific items in MongoDB arrays. It matches array elements based on your query criteria and updates only the targeted fields within those elements.