Check that Field Exists with MongoDB?

In MongoDB, you can check if a field exists in documents using the $exists operator. To ensure the field is not null, combine it with the $ne operator.

Syntax

db.collection.find({ "fieldName": { $exists: true, $ne: null } })

Sample Data

db.checkFieldExistDemo.insertMany([
    {
        "EmployeeId": 1,
        "EmployeeName": "John",
        "isMarried": true,
        "EmployeeSalary": 4648585
    },
    {
        "StudentId": 2,
        "StudentName": "John",
        "isMarried": false,
        "StudentAge": 19
    }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5c76f7b31e9c5dd6f1f78281"),
        ObjectId("5c76f7e11e9c5dd6f1f78282")
    ]
}

Display all documents from the collection ?

db.checkFieldExistDemo.find().pretty();

{
    "_id": ObjectId("5c76f7b31e9c5dd6f1f78281"),
    "EmployeeId": 1,
    "EmployeeName": "John",
    "isMarried": true,
    "EmployeeSalary": 4648585
}
{
    "_id": ObjectId("5c76f7e11e9c5dd6f1f78282"),
    "StudentId": 2,
    "StudentName": "John",
    "isMarried": false,
    "StudentAge": 19
}

Case 1: Field Present in Multiple Documents

Check for the "isMarried" field that exists in both documents ?

db.checkFieldExistDemo.find({ "isMarried": { $exists: true, $ne: null } }).pretty();

{
    "_id": ObjectId("5c76f7b31e9c5dd6f1f78281"),
    "EmployeeId": 1,
    "EmployeeName": "John",
    "isMarried": true,
    "EmployeeSalary": 4648585
}
{
    "_id": ObjectId("5c76f7e11e9c5dd6f1f78282"),
    "StudentId": 2,
    "StudentName": "John",
    "isMarried": false,
    "StudentAge": 19
}

Case 2: Field Present in Single Document

Check for the "StudentName" field that exists only in one document ?

db.checkFieldExistDemo.find({ "StudentName": { $exists: true, $ne: null } }).pretty();

{
    "_id": ObjectId("5c76f7e11e9c5dd6f1f78282"),
    "StudentId": 2,
    "StudentName": "John",
    "isMarried": false,
    "StudentAge": 19
}

Key Points

• $exists: true matches documents where the field is present
• $ne: null excludes documents where the field is null
• Combining both ensures the field exists and has a value

Conclusion

Use $exists: true with $ne: null to check if a field exists and contains a value. This combination filters out both missing fields and null values effectively.