Difference between “id” and “_id” fields in MongoDB

Question

Is there any difference between using the field ID or _ID from a MongoDB document?

I am asking this, because I usually use \"_id\", however I saw this sort({id:-1})

Answer 1

id is an alias for _id in mongoid.id would return the _id of the document. https://github.com/mongodb/mongoid/blob/master/lib/mongoid/fields.rb#L47

if the _id field is not specified an ObjectedId is generated automatically.