MongoDB how to delete document by count fields

My collection has data with 10000+ records in the fields. It has two documents with 111 fields and 7 fields respectively.

I want to delete the document in collection with 7 fields. Please help suggest a query for this problem.

>Solution :

To delete a document with 7 fields, use the db.collection.deleteOne() method with the $expr query operator which allows you to use aggregate operators like $size and $objectToArray to get the number of fields in the document using the system variable $$ROOT as reference to the root document.

The following operation will delete a single document with n number of fields:

var n = 7;
db.collection.deleteOne({
    $expr: {
        $eq: [
            { $size: { $objectToArray: '$$ROOT' } },
            n // n = 7
        ]
    }    
});