How to use $slice operator to get last element of array in MongoDB?

To get the last element of an array in MongoDB, use the $slice operator with -1 in the projection. This returns only the last element of the specified array field.

Syntax

db.collectionName.find(
    {},
    { arrayFieldName: { $slice: -1 } }
);

Sample Data

Let us create a collection with sample student documents ?

db.getLastElementOfArrayDemo.insertMany([
    {
        "StudentName": "James",
        "StudentMathScore": [78, 68, 98]
    },
    {
        "StudentName": "Chris", 
        "StudentMathScore": [88, 56, 34]
    },
    {
        "StudentName": "Larry",
        "StudentMathScore": [99]
    },
    {
        "StudentName": "Robert",
        "StudentMathScore": [90, 78, 67, 66, 75, 73]
    }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5c9d2d71a629b87623db1b2e"),
        ObjectId("5c9d2d83a629b87623db1b2f"),
        ObjectId("5c9d2d8ea629b87623db1b30"),
        ObjectId("5c9d2dada629b87623db1b31")
    ]
}

View All Documents

db.getLastElementOfArrayDemo.find().pretty();

{
    "_id": ObjectId("5c9d2d71a629b87623db1b2e"),
    "StudentName": "James",
    "StudentMathScore": [78, 68, 98]
}
{
    "_id": ObjectId("5c9d2d83a629b87623db1b2f"),
    "StudentName": "Chris",
    "StudentMathScore": [88, 56, 34]
}
{
    "_id": ObjectId("5c9d2d8ea629b87623db1b30"),
    "StudentName": "Larry",
    "StudentMathScore": [99]
}
{
    "_id": ObjectId("5c9d2dada629b87623db1b31"),
    "StudentName": "Robert",
    "StudentMathScore": [90, 78, 67, 66, 75, 73]
}

Get Last Array Element

Use $slice: -1 to retrieve only the last element from each array ?

db.getLastElementOfArrayDemo.find(
    {},
    { StudentMathScore: { $slice: -1 } }
);

{ "_id": ObjectId("5c9d2d71a629b87623db1b2e"), "StudentName": "James", "StudentMathScore": [98] }
{ "_id": ObjectId("5c9d2d83a629b87623db1b2f"), "StudentName": "Chris", "StudentMathScore": [34] }
{ "_id": ObjectId("5c9d2d8ea629b87623db1b30"), "StudentName": "Larry", "StudentMathScore": [99] }
{ "_id": ObjectId("5c9d2dada629b87623db1b31"), "StudentName": "Robert", "StudentMathScore": [73] }

Key Points

• $slice: -1 returns the last element as a single-element array, not a scalar value.
• Works with arrays of any size, including single-element arrays.
• Can be combined with query filters to target specific documents.

Conclusion

The $slice operator with -1 efficiently retrieves the last element from array fields. The result is returned as an array containing only the last element, preserving the array structure in the output.