Chris@0: Description:
Chris@0:   The plugin migration generator assists in working with schema additions 
Chris@0:   required by plugins. Instead of running migrations from plugins directly,
Chris@0:   the generator creates a regular Rails migration which will be responsible
Chris@0:   for migrating the plugins from their current version to the latest version
Chris@0:   installed.
Chris@0:   
Chris@0:   This is important because the set of application migrations remains an
Chris@0:   accurate record of the state of the database, even as plugins are installed
Chris@0:   and removed during the development process.
Chris@0: 
Chris@0: Example:
Chris@0:   ./script/generate plugin_migration [<plugin_name> <another_plugin_name> ...]
Chris@0: 
Chris@0:   This will generate:
Chris@0: 
Chris@0:     RAILS_ROOT
Chris@0:       |- db
Chris@0:           |-migrate
Chris@0:               |- xxx_plugin_migrations.rb
Chris@0: 
Chris@0:   which contains the migrations for the given plugin(s).
Chris@0:   
Chris@0:   
Chris@0: Advanced Usage:
Chris@0: 
Chris@0: There may be situations where you need *complete* control over the migrations
Chris@0: of plugins in your application, migrating a certainly plugin down to X, and
Chris@0: another plugin up to Y, where neither X or Y are the latest migrations for those
Chris@0: plugins.
Chris@0: 
Chris@0: For those unfortunate few, I have two pieces of advice:
Chris@0: 
Chris@0:  1. Why? This is a code smell [http://c2.com/xp/CodeSmell.html].
Chris@0:  
Chris@0:  2. Well, OK. Don't panic. You can completely control plugin migrations by
Chris@0:     creating your own migrations. To manually migrate a plugin to a specific
Chris@0:     version, simply use
Chris@0:     
Chris@0:       Engines.plugins[:your_plugin_name].migrate(version)
Chris@0:       
Chris@0:     where version is the integer of the migration this plugin should end
Chris@0:     up at.
Chris@0:     
Chris@0: With great power comes great responsibility. Use this wisely.