MongoDB query to update only a single item from voting (up and down) records?

To update a single field in MongoDB voting records, use the $inc operator to increment or decrement vote counts. This allows you to modify only the TotalVote field without affecting other document properties.

Syntax

db.collection.update(
    { "field": "matchValue" },
    { $inc: { "fieldToUpdate": incrementValue } }
);

Create Sample Data

Let us first create a collection with voting records ?

db.demo57.insertMany([
    { "Votes": { "VoterName": "Chris", "TotalVote": 50 } },
    { "Votes": { "VoterName": "David", "TotalVote": 101 } }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e285bb8cfb11e5c34d8991a"),
        ObjectId("5e285bc3cfb11e5c34d8991b")
    ]
}

Display all documents from the collection ?

db.demo57.find();

{ "_id": ObjectId("5e285bb8cfb11e5c34d8991a"), "Votes": { "VoterName": "Chris", "TotalVote": 50 } }
{ "_id": ObjectId("5e285bc3cfb11e5c34d8991b"), "Votes": { "VoterName": "David", "TotalVote": 101 } }

Example: Update Single Vote Count

Here is the query to update only David's TotalVote by incrementing it by 19 ?

db.demo57.update(
    { "Votes.VoterName": "David" },
    { $inc: { "Votes.TotalVote": 19 } }
);

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

Verify Result

Display the updated documents ?

db.demo57.find();

{ "_id": ObjectId("5e285bb8cfb11e5c34d8991a"), "Votes": { "VoterName": "Chris", "TotalVote": 50 } }
{ "_id": ObjectId("5e285bc3cfb11e5c34d8991b"), "Votes": { "VoterName": "David", "TotalVote": 120 } }

Key Points

• Use $inc with positive values for upvotes and negative values for downvotes
• Dot notation targets nested fields like "Votes.TotalVote"
• Only the specified field is modified; other document properties remain unchanged

Conclusion

The $inc operator efficiently updates single voting fields by incrementing or decrementing values. This approach ensures atomic updates while preserving the integrity of other document data.