sti_example.rb

class LoggedEvent
  include DataMapper::Mongo::Resource

  property :id,                ObjectID
  property :type,              Discriminator
  property :message,           String
  property :custom_attributes, Hash
  property :created_at,        DateTime
end

class ProjectEvent  < LoggedEvent
  belongs_to :project
end

class ColumnEvent < ProjectEvent
  belongs_to :column
end

class TaskEvent < LoggedEvent
  belongs_to :task
end