If you’re using STI (single table inheritance) with some Ruby on Rails models, and you need to make sure some fields are unique across all the models, you can use validates_uniqueness_of in the parent model using the :scope option to apply it to all the models. So in this instance since you have a type field in the table, you would use:


validates_uniqueness_of :name, :scope => :type


However, you might encounter trouble with type being a deprecated method that is aliased to class. The fix is to add this before the validation:


undef_method :type


Have you ever run “rake db:migrate” on an empty database (or you did “rake db:migrate VERSION=0″ to empty the database). And then it fails on you like this?


rake db:migrate
(in /Users/foucist/rails/myproject)
rake aborted!
Mysql::Error: #42S02Table 'myproject_development.users' doesn't exist: SHOW FIELDS FROM users
(See full trace by running task with --trace)


Invariably, rake failures are caused by something in the environment file that is expecting something in the database. Sometimes people stick a .find() in the environment file unfortunately. In this case, it turned out to be the user observer.


Rails::Initializer.run do |config|
config.action_controller.session_store = :active_record_store
config.active_record.observers = :user_observer
end


After examining the code for the rake tasks in /opt/local/lib/ruby/gems/1.8/gems/rails-1.2.3/lib/tasks/ I noticed that the environment file was loaded with ‘require’. That means that environment.rb is code (obviously) and now I can change the line for the user observer to not load when rake is loading it.


config.active_record.observers = :user_observer unless File.basename( $0 ) == "rake"


Viola. File.basename is just a trick to parse the $0 variable which is the name of the binary thats loading the file.