gistfile1.rb

require "activerecord"

ActiveRecord::Base.establish_connection :adapter => "sqlite3", :database  => "test.sqlite"

class CategoriesMigration < ActiveRecord::Migration
  def self.up
    create_table :categories do |t|
      t.string  :name
      t.string  :type
    end
  end

  def self.down
    drop_table :categories
  end
end

CategoriesMigration.migrate :up

class Category < ActiveRecord::Base
end

class Subcategory < Category
end

Category.create! :name => "Root"
Subcategory.create! :name => "Leaf"

puts Category.last.inspect  # => #<Subcategory id: 2, name: "Leaf", type: "Subcategory">