Display the last two values from field with MongoDB

To display the last two values from a field in MongoDB, use the $slice operator with a negative value in the projection. The negative value indicates retrieving elements from the end of the array.

Syntax

db.collection.find({}, { "fieldName": { "$slice": -N } });

Sample Data

Let us first create a collection with documents ?

db.numberOfValuesDemo.insertOne({
    "Values": [100, 200, 300, 900, 1000, 98]
});

{
    "acknowledged": true,
    "insertedId": ObjectId("5cefb736ef71edecf6a1f6ab")
}

Display all documents from a collection with the help of find() method ?

db.numberOfValuesDemo.find().pretty();

{
    "_id": ObjectId("5cefb736ef71edecf6a1f6ab"),
    "Values": [
        100,
        200,
        300,
        900,
        1000,
        98
    ]
}

Example: Get Last Two Values

Following is the query to get the last two values. Here, we have used negative sign with $slice ?

db.numberOfValuesDemo.find({}, { "Values": { "$slice": -2 } });

{ "_id": ObjectId("5cefb736ef71edecf6a1f6ab"), "Values": [1000, 98] }

Key Points

• $slice: -2 returns the last 2 elements from the array.
• Positive values with $slice return elements from the beginning of the array.
• The projection only affects the returned document structure, not the stored data.

Conclusion

Use $slice with negative values in MongoDB projections to retrieve the last N elements from an array field. This is particularly useful for getting recent entries or the latest values from array fields.