Historical: Versioning and Auditing

There are several plugins available for versioning (e.g. acts_as_versioned, simply_versioned, vestal_versions). Since they try to solve versioning using a relational database they require that you setup table for each model being versioned, clutter your main table or serialize your data into a single TEXT or BLOB field.

Historical doesn't need to look for workarounds since it uses MongoDB as the backend, a document-database which does not require a fixed schema or table structure.

Developed with/for Rails 3.0, installable using Bundler.

# models/message.rb

class Message < ActiveRecord::Base
  # string    :title
  # text      :body
  # datetime  :published_at
  # integer   :author_id
  
  # This is unnecessary if you use Rails (will be installed by default on boot)
  extend Historical::ActiveRecord
  
  is_historical
end

# app.rb

m = Message.create(:title => "foo", :author_id => 1)
m.author = Person.find(2)
m.title = "bar"
m.save!

versions = m.history.versions.all

# get old values
versions[0].title       #=> "foo"
versions[0].author_id   #=> 1

# access an old relation
old = versions[0].restore     #=> <#Message>
old.author                    #=> User(id:1)

# what changed?
versions[1].diff.to_hash      #=> { :author_id => [1, 2], :title => ["foo", "bar"] }
versions[1].diff.changes      #=> [<#AttributeDiff>, <#AttributeDiff>]
versions[1].meta.created_at   #=> 2010-01-23 18:56:52 (date when model was saved)

As you have seen above each version contains a meta-object. You can write custom data to that meta object.

# YourApp.current_user could be set by a before_filter

class AuditedMessage < ActiveRecord::Base

  # This is unnecessary if you use Rails (will be installed by default on boot)
  extend Historical::ActiveRecord
  
  is_historical do
  
    meta do
      # extend that object with MongoMapper helpers
      key :reason, String
      
      belongs_to_active_record :author, :required => true, :class_name => "Person"
    end

    callback do |version|
      version.meta.author   = YourApp.current_user
      version.meta.reason   = "some reason"
    end
  end
end

Historical::Models::ModelVersion.where(:"meta.author_id" => 1).all

The MongoMapper extension belongs_to_active_record creates belongs_to (also polymorphic) relations and will handle key generation.

When calling model.history you will get a object that contains several methods to operate with the history of a model.

• model.history.versions will return a PQ containing all versions for that model. It's sorted ascending by creation date.
• model.history.previous_version, model.history.next_version, model.history.latest_version, model.history.original_version - you get it.
• model.history.find_version(2) like in model.history.versions.all[2] only handled by the database (less db-app traffic).

old_message = message.history.original_version.restore
not_so_old_message = old_message.history.next_version.restore

MongoMapper - which is used by Historical - uses Plucky, a query generator. To perform the query you must call .all on it (similar to ActiveRecord).

Historical won't prevent your model from being destroyed. Should your model be destroyed all versions will be destroyed as well. However you might consider to use is_paranoid by semanticart for that. Historical will then detect updates on the deleted_at column and store a new version.

Note: is_paranoid was discontinued by semanticart in October 2009. I recommend to read about the whys. These are also the reasons why such feature isn't implemented in Historical by itself. You might want to use the less hacky is_paranoid by mislav, who developed will_paginate.

Copyright (c) 2010 Marcel Jackwerth (marcel@northdocks.com). Released under the MIT licence.