vestal_versions¶ ↑

Finally, DRY ActiveRecord versioning!

acts_as_versioned[http://github.com/technoweenie/acts_as_versioned] by technoweenie was a great start, but it failed to keep up with ActiveRecord’s introduction of dirty objects in version 2.1. Additionally, each versioned model needs its own versions table that duplicates most of the original table’s columns. The versions table is then populated with records that often duplicate most of the original record’s attributes. All in all, not very DRY.

vestal_versions[http://github.com/laserlemon/vestal_versions] requires only one versions table (polymorphically associated with its parent models) and no changes whatsoever to existing tables. But it goes one step DRYer by storing a serialized hash of only the models’ changes. Think modern version control systems. By traversing the record of changes, the models can be reverted to any point in time.

And that’s just what vestal_versions does. Not only can a model be reverted to a previous version number but also to a date or time!

In environment.rb:

Rails::Initializer.run do |config|
  ...
  config.gem 'vestal_versions'
  ...
end

At your application root, run:

$ sudo rake gems:install

Next, generate and run the first and last versioning migration you’ll ever need:

$ script/generate vestal_versions
$ rake db:migrate

To version an ActiveRecord model, simply add versioned to your class like so:

class User < ActiveRecord::Base
  versioned

  validates_presence_of :first_name, :last_name

  def name
    "#{first_name} #{last_name}"
  end
end

It’s that easy! Now watch it in action…

>> u = User.create(:first_name => "Steve", :last_name => "Richert")
=> #<User first_name: "Steve", last_name: "Richert">
>> u.version
=> 1
>> u.update_attribute(:first_name, "Stephen")
=> true
>> u.name
=> "Stephen Richert"
>> u.version
=> 2
>> u.revert_to(10.seconds.ago)
=> 1
>> u.name
=> "Steve Richert"
>> u.version
=> 1
>> u.save
=> true
>> u.version
=> 3
>> u.update_attribute(:last_name, "Jobs")
=> true
>> u.name
=> "Steve Jobs"
>> u.version
=> 4
>> u.revert_to!(2)
=> true
>> u.name
=> "Stephen Richert"
>> u.version
=> 5

For the most part, version 1.0 of vestal_versions is backwards compatible, with just a few notable changes:

• The versions table has been beefed up. You’ll need to add the following columns (and indexes, if you feel so inclined):

  change_table :versions do |t|
    t.belongs_to :user, :polymorphic => true
    t.string :user_name
    t.string :tag
  end
  
  change_table :versions do |t|
    t.index [:user_id, :user_type]
    t.index :user_name
    t.index :tag
  end
  

• When a model is created (or updated the first time after being versioned), an initial version record with a number of 1 is no longer created. These aren’t used during reversion and so they end up just being dead weight. Feel free to scrap all your versions where number == 1 after the upgrade if you’d like to free up some room in your database (but you don’t have to).

• Models that have no version records in the database will return a @user.version of 1. In the past, this would have returned nil instead.

• Version has moved to VestalVersions::Version to make way for custom version classes.

• Version#version did not survive the move to VestalVersions::Version#version. That alias was dropped (too confusing). Use VestalVersions::Version#number.

There are a handful of exciting new additions in version 1.0 of vestal_versions. A lot has changed in the code: much better documentation, more modular organization of features, and a more exhaustive test suite. But there are also a number of new features that are available in this release of vestal_versions:

• The ability to completely skip versioning within a new skip_version block:

  @user.version # => 1
  @user.skip_version do
    @user.update_attribute(:first_name, "Stephen")
    @user.first_name = "Steve"
    @user.save
    @user.update_attributes(:last_name => "Jobs")
  end
  @user.version # => 1
  

  Also available, are merge_version and append_version blocks. The merge_version block will compile the possibly multiple versions that would result from the updates inside the block into one summary version. The single resulting version is then tacked onto the version history as usual. The append_version block works similarly except that the resulting single version is combined with the most recent version in the history and saved.

• Version tagging. Any version can have a tag attached to it (must be unique within the scope of the versioned parent) and that tag can be used for reversion.

  @user.name # => "Steve Richert"
  @user.update_attribute(:last_name, "Jobs")
  @user.name # => "Steve Jobs"
  @user.tag_version("apple")
  @user.update_attribute(:last_name, "Richert")
  @user.name # => "Steve Richert"
  @user.revert_to("apple")
  @user.name # => "Steve Jobs"
  

  So if you’re not big on version numbers, you could just tag your versions and avoid the numbers altogether.

• Resetting. This is basically a hard revert. The new reset_to! instance method behaves just like the revert_to! method except that after the reversion, it will also scrap all the versions that came after that target version.

  @user.name # => "Steve Richert"
  @user.version # => 1
  @user.versions.count # => 0
  @user.update_attribute(:last_name, "Jobs")
  @user.name # => "Steve Jobs"
  @user.version # => 2
  @user.versions.count # => 1
  @user.reset_to!(1)
  @user.name # => "Steve Richert"
  @user.version # => 1
  @user.versions.count # => 0
  

• Storing which user is responsible for a revision. Rather than introduce a lot of controller magic to guess what to store, you can simply update an additional attribute on your versioned model: updated_by.

  @user.update_attributes(:last_name => "Jobs", :updated_by => "Tyler")
  @user.versions.last.user # => "Tyler"
  

  Instead of passing a simple string to the updated_by setter, you can pass a model instance, such as an ActiveRecord user or administrator. The association will be saved polymorphically alongside the version.

  @user.update_attributes(:last_name => "Jobs", :updated_by => current_user)
  @user.versions.last.user # => #<User first_name: "Steven", last_name: "Tyler">
  

• Global configuration. The new vestal_versions Rails generator also writes an initializer with instructions on how to set application-wide options for the versioned method.

• Conditional version creation. The versioned method now accepts :if and :unless options. Each expects a symbol representing an instance method or a proc that will be evaluated to determine whether or not to create a new version after an update. An array containing any combination of symbols and procs can also be given.

  class User < ActiveRecord::Base
    versioned :if => :really_create_a_version?
  end
  

• Custom version classes. By passing a :class_name option to the versioned method, you can specify your own ActiveRecord version model. VestalVersions::Version is the default, but feel free to stray from that. I recommend that your custom model inherit from VestalVersions::Version, but that’s up to you!

• A versioned? convenience class method. If your user model is versioned, User.versioned? will let you know.

• Fixed Tagging class naming conflict with acts-as-taggable-on.

Thank you to all those who post issues and suggestions. And special thanks to:

• splattael, who first bugged (and helped) me to write some tests for this thing

• snaury, who helped out early on with the between association method, the :dependent option and a conflict from using a method called changes

• sthapit, who was responsible for the :only and :except options as well as showing me that I’m a dummy for storing a useless first version

To contribute to vestal_versions, please fork, hack away in the integration branch and send me a pull request. Remember your tests!