active record without rails using sqlite in memory

ar.rb

require 'active_record'
require 'sqlite3'

ActiveRecord::Base.establish_connection(
 adapter:  'sqlite3',
 database: ':memory:'
)


ActiveRecord::Schema.define do
  create_table :comments , force: true do |t|
    t.string :name
  end

  create_table :posts , force: true do |t|
    t.string :name
    t.belongs_to :show, index: true
  end
end

class Show < ActiveRecord::Base
end

puts Show.column_names
show = Show.new
puts show.inspect