Implementing MongoDB exists and ne?

The $exists operator checks whether a field exists in a document, while $ne (not equal) filters documents where a field value does not match the specified value. Combining both operators helps find documents with existing fields that contain meaningful data.

Syntax

// $exists operator
db.collection.find({ "fieldName": { "$exists": true/false } });

// $ne operator  
db.collection.find({ "fieldName": { "$ne": "value" } });

// Combined usage
db.collection.find({
    "$and": [
        { "fieldName": { "$exists": true } },
        { "fieldName": { "$ne": "unwantedValue" } }
    ]
});

Sample Data

db.existsDemo.insertMany([
    { "Name": "Chris", "Age": 21 },
    { "Name": "", "Age": null },
    { "Name": null, "Age": 24 },
    { "Age": 23 }
]);

Display All Documents

db.existsDemo.find().pretty();

{
   "_id" : ObjectId("5cd7c3916d78f205348bc650"),
   "Name" : "Chris",
   "Age" : 21
}
{ "_id" : ObjectId("5cd7c39a6d78f205348bc651"), "Name" : "", "Age" : null }
{ "_id" : ObjectId("5cd7c3a66d78f205348bc652"), "Name" : null, "Age" : 24 }
{ "_id" : ObjectId("5cd7c3c36d78f205348bc653"), "Age" : 23 }

Example: Find Documents with Non-Empty Name Field

Find documents where the "Name" field exists and is not an empty string ?

db.existsDemo.find({
    "$and": [
        { "Name": { "$exists": true } },
        { "Name": { "$ne": "" } }
    ]
});

{ "_id" : ObjectId("5cd7c3916d78f205348bc650"), "Name" : "Chris", "Age" : 21 }
{ "_id" : ObjectId("5cd7c3a66d78f205348bc652"), "Name" : null, "Age" : 24 }

Key Points

• $exists: true matches documents where the field is present, even if the value is null
• $exists: false matches documents where the field is completely missing
• $ne matches all values except the specified one, including null
• Combining both operators helps filter for fields with meaningful non-empty values

Conclusion

Use $exists and $ne together to find documents with existing fields that contain meaningful data. This combination is particularly useful for filtering out empty strings, null values, or missing fields in query results.