How to loop through collections with a cursor in MongoDB?

In MongoDB, you can loop through collections with a cursor using the while loop with hasNext() and next() methods. A cursor is returned by the find() method and allows you to iterate through documents one by one.

Syntax

var cursor = db.collectionName.find();
while(cursor.hasNext()) {
    var document = cursor.next();
    printjson(document);
}

Create Sample Data

Let us create a collection with student documents ?

db.loopThroughCollectionDemo.insertMany([
    {"StudentName": "John", "StudentAge": 23},
    {"StudentName": "Larry", "StudentAge": 21},
    {"StudentName": "Chris", "StudentAge": 25},
    {"StudentName": "Robert", "StudentAge": 24}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5c9ca81f2d6669774125247f"),
        ObjectId("5c9ca8272d66697741252480"),
        ObjectId("5c9ca8462d66697741252481"),
        ObjectId("5c9ca8632d66697741252482")
    ]
}

Verify Sample Data

db.loopThroughCollectionDemo.find().pretty();

{
    "_id": ObjectId("5c9ca81f2d6669774125247f"),
    "StudentName": "John",
    "StudentAge": 23
}
{
    "_id": ObjectId("5c9ca8272d66697741252480"),
    "StudentName": "Larry",
    "StudentAge": 21
}
{
    "_id": ObjectId("5c9ca8462d66697741252481"),
    "StudentName": "Chris",
    "StudentAge": 25
}
{
    "_id": ObjectId("5c9ca8632d66697741252482"),
    "StudentName": "Robert",
    "StudentAge": 24
}

Example: Loop Through Collection with Cursor

Use a while loop to iterate through all documents ?

var allDocumentValue;
var cursor = db.loopThroughCollectionDemo.find();
while(cursor.hasNext()) {
    allDocumentValue = cursor.next();
    printjson(allDocumentValue);
}

{
    "_id": ObjectId("5c9ca81f2d6669774125247f"),
    "StudentName": "John",
    "StudentAge": 23
}
{
    "_id": ObjectId("5c9ca8272d66697741252480"),
    "StudentName": "Larry",
    "StudentAge": 21
}
{
    "_id": ObjectId("5c9ca8462d66697741252481"),
    "StudentName": "Chris",
    "StudentAge": 25
}
{
    "_id": ObjectId("5c9ca8632d66697741252482"),
    "StudentName": "Robert",
    "StudentAge": 24
}

Key Points

• Cursor − Returned by find() method for iterating through documents
• hasNext() − Returns true if more documents exist in the cursor
• next() − Returns the next document and advances the cursor
• printjson() − Formats and displays the document in readable JSON

Conclusion

MongoDB cursors provide an efficient way to loop through large collections. Use hasNext() and next() methods with a while loop to process documents individually without loading all data into memory at once.