Store changes for any model

event_logger.rb

class Magazine::EventLogger

  attr_reader :history

  FIELD_EXCEPTIONS = [:updated_at]

  @namespace = 'Magazine::'
  @suffix = 'Event'

  def initialize(object)
    @object = object
    @history = {}
  end

  # store changed fields in hast and thet to DB
  def process
    changed_keys = @object.changed_attributes.keys
    changed_keys.each do |key|
       next if FIELD_EXCEPTIONS.include?(key.to_sym)

       @history[key] = {before: preprocess_attribute(@object.changed_attributes[key], key),
                    now: preprocess_attribute(@object.attributes[key], key) }
    end
  end
 
  # you can let logger to define owner class and id automaticaly or set them manualy
  def write(owner_type = nil, owner_id = nil)
    process
    content = @history.to_json
    type = owner_type || "#{@namespace}#{@object.class.name.demodulize}#{@suffix}"
    Magazine::Event.create(owner_id: owner_id || @object.id, content: content, type: type)
  end

  def preprocess_attribute(value, key)
     return value if value.blank?
     result = case @object.class.columns_hash[key].type
                when :datetime then I18n.l(value, format: :date_time)
                when :boolean then (value ? 'Yes' : 'No')
                else value
              end
    return result
  end

end

# subscribe some model without of any params
#  
#  after_save :log_changes
#  def log_changes
#    logger = Magazine::EventLogger.new(self)
#    logger.write
#  end
# or set class and id (Link model belongs_to Set and I want to save Link events as Set events)
#  def log_changes
#    logger = Magazine::EventLogger.new(self)
#    logger.write('Magazine::SetEvent', set.id)
#  end