* Observer pattern:

  class MyObserver < Sequel::Observer
    observe Item, Post

    def after_save
      ...
    end
  end

* Smarter one_to_one: stuff like:

  # assuming the Author's primary key is :name
  post = Post.create(:name => 'The Lover', :author => Author['A.B. Yehoshua'])
  post.set(:author => Author['A.B. Yehoshua'])
  
  Book.filter_by_author(Author[:name => 'Kurt Vonnegut']).print

  #and also
  post = Post.create(:name => 'The Lover', :author => 'A.B. Yehoshua') #=> fetches the author record
  post.set(:author => 'A.B. Yehoshua')

* many_to_many smart relationships.