This for loop is working and updating all
records using mongodb loop and the example as given below.
//Find Items from collection.
var items
= db.collection.find(), i = 0;
//For-each loop execution.
items.forEach(function(item){
db.collection.update(
{_id: item._id},
{$set:{new_field:i}
});
$i++;
});
For more detail, go to link