Return True if a document exists in MongoDB?

To check if a document exists in MongoDB, use the find() method with count() or limit(1) to return a boolean result. The count() > 0 approach returns true if documents match the query criteria.

Syntax

db.collection.find(query).count() > 0

Create Sample Data

First, let's create a collection with sample documents ?

db.documentExistsOrNotDemo.insertMany([
    {"UserId": 101, "UserName": "John"},
    {"UserId": 102, "UserName": "Chris"},
    {"UserId": 102, "UserName": "Robert"}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5c9932bd330fd0aa0d2fe4cf"),
        ObjectId("5c9932c6330fd0aa0d2fe4d0"),
        ObjectId("5c9932ce330fd0aa0d2fe4d1")
    ]
}

Display all documents to verify the data ?

db.documentExistsOrNotDemo.find().pretty();

{
    "_id": ObjectId("5c9932bd330fd0aa0d2fe4cf"),
    "UserId": 101,
    "UserName": "John"
}
{
    "_id": ObjectId("5c9932c6330fd0aa0d2fe4d0"),
    "UserId": 102,
    "UserName": "Chris"
}
{
    "_id": ObjectId("5c9932ce330fd0aa0d2fe4d1"),
    "UserId": 102,
    "UserName": "Robert"
}

Case 1: Document Exists (Returns True)

Check if a document with UserId 101 exists ?

db.documentExistsOrNotDemo.find({"UserId": 101}).count() > 0;

true

Case 2: Document Does Not Exist (Returns False)

Check if a document with UserId 110 exists ?

db.documentExistsOrNotDemo.find({"UserId": 110}).count() > 0;

false

Alternative Method: Using limit(1)

For better performance with large collections, use limit(1) to stop after finding the first match ?

db.documentExistsOrNotDemo.find({"UserId": 101}).limit(1).count() > 0;

true

Conclusion

Use find(query).count() > 0 to check document existence in MongoDB. This returns true if matching documents exist, false otherwise. For large collections, combine with limit(1) for better performance.