Mongoid has two ways to define field aliases:

class Band
  include Mongoid::Document

  # case 1
  field :n, type: String
  alias_attribute :name, :n

  # case 2
  field :a, as: :age
end

Band.database_field_name(:name) #=> "n"
Band.database_field_name(:age) #=> "a"

Mongoid has several 100s of tests today which cover field alias related behavior. In most tests, only case 2 (:as) is covered. We should review all tests to ensure that both patterns are covered in all cases.