Self-referential rails example

create_people.rb

class CreatePeople < ActiveRecord::Migration
  def change
    create_table :people do |t|
      t.string :name

      t.timestamps
    end
  end
end

create_person_relationships.rb

class CreatePersonRelationships < ActiveRecord::Migration
  def change
    create_table :person_relationships do |t|
      t.integer :parent_id
      t.integer :child_id

      t.timestamps
    end
  end
end

schema.rb

ActiveRecord::Schema.define(:version => 20100401133415) do

  create_table "people", :force => true do |t|
    t.string   "name"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "person_relationships", :force => true do |t|
    t.integer  "parent_id"
    t.integer  "child_id"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

end