SimplyVersioned
===============
Release:  1.0.0
Date:      28-01-2008
Author:    Matt Mower <self@mattmower.com>
SimplyVersioned is a simple, non-invasive, approach to versioning ActiveRecord models.
SimplyVersioned does not require any structural change to the models to be versioned and requires only one versions 
table to be created (a migration generator is supplied with the plugin) for the application, regardless of the number of 
models being versioned.
The plugin introduces a 'Version' ActiveRecord model (that reflects changes to model attributes) to which versioned 
models are polymorphically associated. Version records store the model information as a YAML hash.
  
SimplyVersioned meets a simple need for model versioning. If your needs are more complex maybe try Rick Olsen's 
acts_as_versioned (https://svn.techno-weenie.net/projects/plugins/acts_as_versioned/).
  
SimplyVersioned is (so far) actively tested with Rails 2.0.2 and Ruby 1.8.6
  
Usage
=====
1. Install the plugin
  ./script/plugin install https://rubymatt.rubyforge.org/svn/simply_versioned
2. Generate the migration
  ./script/generate simply_versioned_migration
  Note that the migration defaults to storing the version info in a TEXT field. On MySQL this will default to a
  limit of 64K. If you are versioning particularly large models you will want to modify the migration to include
  a :limit => n condition to promote the yaml column to a MEDIUMTEXT or (god forbid) a LONGTEXT.
3. Create the versions table
  rake db:migrate
4. Annotate the models you want to version specifying how many versions to keep
  class Thing < ActiveRecord::Base
    simply_versioned :keep => 10
  end
  
  If you do not specify a limit then old versions are never automatically deleted. You can
  manually delete them like this:
  
  thing.versions.purge( 10 )
  
  which would delete all the but the last ten versions.
  
  If you want fine-grained control over when versions are created you can use:
  
  class Thing < ActiveRecord::Base
    simply_versioned :automatic => false
  end
  
  and new versions will no longer be created by default. You will then need to use
  the with_versioning method to create a version.
  
  Lastly you can control which columns will be versioned by specifying an exclude parameter.
  
  class Thing < ActiveRecord::Base
    simply_versioned :exclude => :awkward_column
  end
    
  or  
  
  class Thing < ActiveRecord::Base
    simply_versioned :exclude => [:first_awkward_column,:second_awkward_column,...]
  end
  
  This may be helpful if you run into conflicts with other plugins which try to manage columns.
5. Create versions
  thing = Thing.create!( :foo => bar ) # creates v1
  thing.foo = baz
  thing.save! # creates v2
  
  If you need to control whether a version is created or not, use #with_versioning. For example:
  
  thing.with_versioning( false ) do |t|
    t.save!
  end
  
  or, using the "magic pen" (https://dablog.rubypal.com/2007/2/18/the-magic-pens-of-ruby thanks hmj):
  
  thing.with_versioning( false, &:save! )
6. Find versions
  thing.versions.each do |version| ... end
  render :partial => 'thing_version', :collection => thing.versions
  thing.versions.current
  thing.versions.first
  thing.versions.get( 3 )
  
  To find a version number:
  
  thing.version_number
7. Revert to a previous version
  thing.revert_to_version( 5 )
  
  If a specific reversion needs to avoid overwriting some column values pass
  an :except option, e.g.
  
  thing.revert_to_version( 1, :except => [:name,:age] )
  
  The revert_to_version method also takes an existing Version instance, e.g.
  
  version = thing.versions.find( ... )
  thing.revert_to_version( version )
8. Traverse versions
  thing.versions.current.previous
  thing.versions.first.next
9. Obtain a copy of a previous versioned model
  thing.versions.first.model # => Instantiated Thing with versioned values
  
Thanks to:
  Chris Wanstrath (https://ozmm.org/) for useful feedback and GitHub
  Josh Susser (https://blog.hasmanythrough.com/) for useful suggestions and feedback
  Rick Olson (https://techno-weenie.net/) for all the many plugins whose code i've read
  
Copyright (c) 2007 Matt Mower <self@mattmower.com> and released under the MIT license