ruby - Mongoid returns inconsistent doc id after multiple upserts of the same document -

i'm using mongoid gem in ruby. each time upsert, save or insert same unique document in collection, ruby instance shows different id. example, have script so:

class user   include mongoid::document   field :email, type: string   field :name, type: string   index({ email: 1}, { unique: true })   create_indexes end  u=user.new(email: 'test@testers.edu', name: "mr. testy") u.upsert puts u.to_json 

the first time run against empty or non-existent collection, output

{"_id":"52097dee5feea8384a000001","email":"test@testers.edu","name":"mr. testy"} 

if run again, this:

{"_id":"52097e805feea8575a000001","email":"test@testers.edu","name":"mr. testy"} 

but document in mongodb still shows first id (52097dee5feea8384a000001), know operating on same record. if follow upsert find_by operation, right id consistently, feels inefficient have run upsert followed query.

am doing wrong? i'm concerned getting wrong id in operation is, say, updating profile repeatedly.