Remove null element from MongoDB array?

To remove null elements from a MongoDB array, use the $pull operator. This operator removes all instances of specified values from an array field, making it perfect for eliminating null entries.

Syntax

db.collection.update(
    { /* query criteria */ },
    { $pull: { "arrayField": null } }
);

Sample Data

Let us create a collection with documents containing null values in arrays ?

db.removeNullDemo.insertMany([
    {
        "_id": 1,
        "StudentDetails": [
            {
                "FirstName": "John",
                "LastName": "Smith"
            },
            {
                "Age": 21
            },
            null
        ]
    },
    {
        "_id": 2,
        "StudentDetails": [
            {
                "FirstName": "Carol",
                "LastName": "Taylor"
            },
            {
                "Age": 23
            }
        ]
    }
]);

{ "acknowledged": true, "insertedIds": [1, 2] }

Display Current Data

db.removeNullDemo.find().pretty();

{
    "_id": 1,
    "StudentDetails": [
        {
            "FirstName": "John",
            "LastName": "Smith"
        },
        {
            "Age": 21
        },
        null
    ]
}
{
    "_id": 2,
    "StudentDetails": [
        {
            "FirstName": "Carol",
            "LastName": "Taylor"
        },
        {
            "Age": 23
        }
    ]
}

Remove Null Elements

Use $pull to remove null values from the StudentDetails array ?

db.removeNullDemo.update(
    { _id: 1 },
    { $pull: { StudentDetails: null } }
);

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

Verify Result

db.removeNullDemo.find().pretty();

{
    "_id": 1,
    "StudentDetails": [
        {
            "FirstName": "John",
            "LastName": "Smith"
        },
        {
            "Age": 21
        }
    ]
}
{
    "_id": 2,
    "StudentDetails": [
        {
            "FirstName": "Carol",
            "LastName": "Taylor"
        },
        {
            "Age": 23
        }
    ]
}

Remove Null from All Documents

To remove null values from all documents in the collection, use an empty query filter ?

db.removeNullDemo.updateMany(
    {},
    { $pull: { StudentDetails: null } }
);

Conclusion

The $pull operator effectively removes null elements from MongoDB arrays. Use update() for single documents or updateMany() to clean null values across multiple documents in one operation.