event tracking with mongoid

application_helper.rb

module ApplicationHelper

  def event_autolink(event_parts)
    event_parts.map do |part|
      case part.content
      when Hash
        link_to part.content['name'], send("admin_#{part.content['class_name'].underscore}_path", part.content['id'])
      else
        part.content
      end
    end.join(' ').html_safe
  end

end

event.rb

class Event

  include Mongoid::Document
  include Mongoid::Timestamps

  embeds_many :event_parts

  paginates_per 50

  def self.record(*parts)
    Event.create(event_parts: parts.map { |part| EventPart.serialize_and_initialize(part) })
  end

  def self.fetch(*parts)
    parts.inject(Event) do |criteria, part|
      if part.class.superclass == ActiveRecord::Base
        criteria.where('event_parts.content.class_name' => part.class.name, 'event_parts.content.id' => part.id)
      else
        criteria.where('event_parts.content' => part)
      end
    end
  end

end

class EventPart

  include Mongoid::Document

  embedded_in :event

  field :content

  def self.serialize_and_initialize(obj)
    if obj.class.superclass == ActiveRecord::Base
      EventPart.new(content: { name: obj.name, class_name: obj.class.name, id: obj.id })
    else
      EventPart.new(content: obj)
    end
  end

end

event_spec.rb

require 'spec_helper'

describe Event do
  let(:user) { FactoryGirl.create(:user, fname: 'John', lname: 'Doe') }
  let(:subject) { FactoryGirl.create(:subject) }

  it 'should record an Event of varying parts' do
    event = Event.record(user, 'enrolled in', subject, 'and it was good')

    event.should have(4).event_parts
    event.event_parts.first.content.should eq({
      name: 'John Doe',
      class_name: 'User',
      id: user.id
    })
    event.event_parts.last.content.should eq('and it was good')
  end

  it 'should fetch events for some object' do
    Event.record(user, 'signed up')
    Event.record(user, 'enrolled in', subject)
    events = Event.fetch(user)

    events.size.should eq(2)
  end
end

describe EventPart do
  let(:user) { FactoryGirl.create(:user, fname: 'John', lname: 'Doe') }

  it 'should serialize and initialize an EventPart from a user' do
    event_part = EventPart.serialize_and_initialize(user)
    event_part.content.should eq({
      name: 'John Doe',
      class_name: 'User',
      id: user.id
    })
  end
end

events.rb

ActiveAdmin.register_page 'Events' do

  menu if: proc{ can?(:manage, Event) }, parent: 'Logs'

  content do
    table class: 'index_table' do
      thead do
        tr do
          th 'Event'
          th 'When'
        end
      end
      tbody do
        (@events = Event.desc(:created_at).page(params[:page])).each do |event|
          tr class: cycle('odd', 'even') do
            td event_autolink(event.event_parts)
            td do
              span style: 'white-space: nowrap' do
                event.created_at.strftime("%b %d, %Y %I:%M:%S %p")
              end
            end
          end
        end        
      end
    end

    div id: 'index_footer' do
      paginate @events
    end
  end 

end

usage.rb

Event.record(user, 'signed up')
Event.record(user, 'enrolled in', subject)
Event.record(product, 'sold out')

Event.fetch(user) # all of a user's events
Event.fetch(user, 'enrolled in', subject) # events where a user enrolled in a particular subject
Event.fetch(user, subject) # all events associated with a user and a particular subject
Event.fetch('signed up') # all signup events