Perform conditional upserts or updates in MongoDB

In MongoDB, you can perform conditional updates that only modify a field if certain conditions are met. The $max operator is particularly useful for conditional updates - it only updates a field if the new value is greater than the current value.

Syntax

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

Sample Data

Let us create a collection with sample student score documents ?

db.conditionalUpdatesDemo.insertMany([
    {
        "_id": 100,
        "StudentFirstScore": 89,
        "StudentSecondScore": 78,
        "BiggestScore": 89
    },
    {
        "_id": 101,
        "StudentFirstScore": 305,
        "StudentSecondScore": 560,
        "BiggestScore": 1050
    },
    {
        "_id": 103,
        "StudentFirstScore": 560,
        "StudentSecondScore": 789,
        "BiggestScore": 880
    }
]);

{
    "acknowledged": true,
    "insertedIds": [100, 101, 103]
}

Display all documents from the collection ?

db.conditionalUpdatesDemo.find().pretty();

{
    "_id": 100,
    "StudentFirstScore": 89,
    "StudentSecondScore": 78,
    "BiggestScore": 89
}
{
    "_id": 101,
    "StudentFirstScore": 305,
    "StudentSecondScore": 560,
    "BiggestScore": 1050
}
{
    "_id": 103,
    "StudentFirstScore": 560,
    "StudentSecondScore": 789,
    "BiggestScore": 880
}

Example: Conditional Update with $max

Update the BiggestScore field to 150, but only if 150 is greater than the current value ?

db.conditionalUpdatesDemo.update(
    { "_id": 100 },
    { $max: { "BiggestScore": 150 } }
);

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

Verify Result

Check if the BiggestScore field was updated for document with _id 100 ?

db.conditionalUpdatesDemo.find();

{
    "_id": 100,
    "StudentFirstScore": 89,
    "StudentSecondScore": 78,
    "BiggestScore": 150
}
{
    "_id": 101,
    "StudentFirstScore": 305,
    "StudentSecondScore": 560,
    "BiggestScore": 1050
}
{
    "_id": 103,
    "StudentFirstScore": 560,
    "StudentSecondScore": 789,
    "BiggestScore": 880
}

Key Points

• The $max operator only updates the field if the new value is greater than the existing value
• If the new value is smaller or equal, no update occurs
• This provides automatic conditional logic without complex queries

Conclusion

The $max operator provides an elegant solution for conditional updates in MongoDB, automatically comparing values and updating only when the new value exceeds the current one. This is particularly useful for maintaining maximum scores or highest values.