class CustomField
  attr_reader :value

  def initialize(value)
    @value= value.to_s
  end

  def to_s
    value
  end

  def as_json
    value
  end

  # Converts an object of this instance into a database friendly value.
  def mongoize
    @mongoize||= Base64.encode64(value)
  end

  # Get the object as it was stored in the database, and instantiate
  # this custom class from it.
  def self.demongoize(object)
    self.new(Base64.decode64(object))
  end

  # Takes any possible object and converts it to how it would be
  # stored in the database.
  def self.mongoize(object)
    self.new(object).mongoize
  end

  # Converts the object that was supplied to a criteria and converts it
  # into a database friendly form.
  def self.evolve(object)
    self.new(object).mongoize
  end
end

class Report
  include Mongoid::Document

  field :my_field, type: CustomField
end

Report.delete_all
Report.create!(my_field: 'test')
my_field = Report.first.my_field
puts my_field # => expected 'test', actual 'test'
puts my_field.class # => expected CustomField, actual CustomField
my_field = Report.pluck(:my_field).first
puts my_field # => requested 'test', currently "dGVzdA=="
puts my_field.class # => requested CustomField, currently String