How to count a cursor's iteration in MongoDB?

To count a cursor's iteration in MongoDB, you need to use custom logic with a while loop along with a find() cursor. This allows you to iterate through documents and count specific conditions during traversal.

Syntax

var cursor = db.collection.find();
var count = 0;
while (cursor.hasNext()) {
    var document = cursor.next();
    // Apply your counting logic here
    if (condition) {
        count++;
    }
}

Sample Data

db.demo724.insertMany([
    {
        details: {
            id: 101,
            otherDetails: [
                { Name: "Chris" }
            ]
        }
    },
    {
        // Empty document
    },
    {
        details: {
            id: 1001
        }
    }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5eab0cce43417811278f5890"),
        ObjectId("5eab0cce43417811278f5891"),
        ObjectId("5eab0cce43417811278f5892")
    ]
}

Display all documents from the collection ?

db.demo724.find();

{ "_id": ObjectId("5eab0cce43417811278f5890"), "details": { "id": 101, "otherDetails": [ { "Name": "Chris" } ] } }
{ "_id": ObjectId("5eab0cce43417811278f5891") }
{ "_id": ObjectId("5eab0cce43417811278f5892"), "details": { "id": 1001 } }

Example: Count Documents with "details" Field

var c = db.demo724.find();
var detailsCount = 0;
while (c.hasNext()) {
    var current = c.next();
    if (typeof current["details"] != "undefined") {
        detailsCount++;
    }
}
print("Number of details: " + detailsCount);

Number of details: 2

How It Works

• hasNext() checks if more documents exist in the cursor
• next() retrieves the current document and advances the cursor
• Custom condition logic determines when to increment the counter
• The loop continues until all documents are processed

Conclusion

Use cursor iteration with while loops to implement custom counting logic in MongoDB. This approach gives you full control over which documents to count based on specific field conditions or complex criteria.