Update MongoDB collection using $toLower

Question

I have an existing MongoDB collection containing user names. The user names contain both lower case and upper case letters.

I want to update all the user names so th

Answer 1

A little late to the party but the below answer works very well with mongo 3.4 and above First get only those records which have different case and update only those records in bulk. The performance of this query is multifold better

var bulk = db.myCollection.initializeUnorderedBulkOp();
var count = 0
db.myCollection.find({userId:{$regex:'.*[A-Z]'}}).forEach(function(e) {
 var newId = e.userId.toLowerCase();   
    bulk.find({_id:e._id}).updateOne({$set:{userId: newId}})
    count++
    if (count % 500 === 0) {
        bulk.execute();
        bulk = db.myCollection.initializeUnorderedBulkOp();
        count = 0;
    }
})
if (count > 0)  bulk.execute();