How do I check whether a field contains null value in MongoDB?

To check whether a field contains a null value in MongoDB, use the $type operator with type number 10 (which represents null) or compare the field directly with null.

Syntax

// Method 1: Using $type operator
db.collection.find({ fieldName: { $type: 10 } });

// Method 2: Direct null comparison
db.collection.find({ fieldName: null });

Sample Data

Let us create a collection with documents, including one with a null field ?

db.nullDemo.insertMany([
    { "FirstName": "Chris" },
    { "FirstName": null },
    { "FirstName": "Robert" }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5cc68a1eac184d684e3fa270"),
        ObjectId("5cc68a25ac184d684e3fa271"),
        ObjectId("5cc68a2cac184d684e3fa272")
    ]
}

Display all documents to see the data structure ?

db.nullDemo.find();

{ "_id": ObjectId("5cc68a1eac184d684e3fa270"), "FirstName": "Chris" }
{ "_id": ObjectId("5cc68a25ac184d684e3fa271"), "FirstName": null }
{ "_id": ObjectId("5cc68a2cac184d684e3fa272"), "FirstName": "Robert" }

Method 1: Using $type Operator

Check for null values using $type: 10 ?

db.nullDemo.find({ FirstName: { $type: 10 } });

{ "_id": ObjectId("5cc68a25ac184d684e3fa271"), "FirstName": null }

Method 2: Direct Null Comparison

Alternatively, compare the field directly with null ?

db.nullDemo.find({ FirstName: null });

{ "_id": ObjectId("5cc68a25ac184d684e3fa271"), "FirstName": null }

Key Differences

• $type: 10 finds fields that are explicitly null
• fieldName: null finds both null values and missing fields

Conclusion

Use $type: 10 to find explicitly null fields, or fieldName: null to find both null and missing fields. The $type operator provides more precise control when checking for null values specifically.