I have problem when I am trying to use update_all method on field which is readonly.

My User model is -

class User
include Mongoid::Document
field :name, type: String
attr_readonly :name
end

NOTE: Here name is readonly attribute

When I am trying to use update_all it is allowing me to update value of readonly field

2.1.3 :017 > User.all.to_a
=> #<User _id: 54e855837368773ff7000000, name: "Shweta">, #<User _id: 54e855877368773ff7010000, name: "Anuja">

2.1.3 :018 > User.where(name: 'Shweta').update_all(name: 'Shweta k')
=>

{"updatedExisting"=>true, "n"=>1, "connectionId"=>20, "err"=>nil, "ok"=>1.0}

2.1.3 :019 > User.all.to_a
=> #<User _id: 54e855837368773ff7000000, name: "Shweta k">, #<User _id: 54e855877368773ff7010000, name: "Anuja">

When I am using update_attribute, Its giving me ReadonlyAttribute error

2.1.3 :021 > User.first.update_attribute(:name, 'Shweta')
Mongoid::Errors::ReadonlyAttribute:

Is this a bug or I am missing something?