mongoid_field_history.rb

# app/models/concerns/history_field_concern.rb
module HistoryFieldConcern
  extend ActiveSupport::Concern

  # consider using "before_save" and Changable
  # https://github.com/mongodb/mongoid/blob/master/lib/mongoid/changeable.rb
  
  included do
  end

  class_methods do

    # @param name [Symbol]
    # @param opts [Hash]
    def history_field(name, opts)
      field name, opts
      field "#{name}_history", type: Array, default: -> { Array.new }
    end

    # @param name [Symbol]
    def history_belongs_to(model)
      belongs_to model # it creates field :"model_id"
      field "#{model}_id_history", type: Array, default: -> { Array.new }
    end

  end
  
end

class Reservation
  include Mongoid::Document
  include Mongoid::Timestamps
  include HistoryFieldConcern

  field :synced_at, type: Time # sync time with client

  field :removed, type: Boolean, default: false

  history_field :name, type: String, default: nil
  
  belongs_to :salon
  history_belongs_to :master


end

class Master
  include Mongoid::Document
  include Mongoid::Timestamps
  include HistoryFieldConcern

  history_field :first_name, type: String
  # ...

end