mysql2_example.rb

require 'pry'
require 'ffaker'
require 'active_record'

database = 'test'

config = {
  adapter:  'mysql2',
  encoding: 'utf8',
  username: 'root',
  host:     '127.0.0.1',
  port:     3306
}

ActiveRecord::Base.configurations = { 'test' => config }
ActiveRecord::Base.establish_connection(:test)

class Architect
  def add_brands
    brands = 3.times.map { |_| { name: Faker::Product.brand } }
    
    Brand.create(brands)
    puts "Added 3 brands..."
  end
end

@from_scratch = false

ActiveRecord::Base.connection.recreate_database(database, config) if @from_scratch

binding.pry

ActiveRecord::Base.configurations = { 'test' => config.merge(database: database) }
ActiveRecord::Base.establish_connection(:test)

require './db/schema.rb' if @from_scratch

(ActiveRecord::Base.connection.tables - %w[schema_migrations]).each do |table|
  Object.const_set(table.classify, Class.new(ActiveRecord::Base))
end

Architect.new.add_brands

test.rb

gem 'rails'
gem 'foreigner'

require 'active_record'
require 'foreigner'

begin
  config = {
    'database'     => 'temp_database',
    'adapter'      => 'postgresql',
    'username'     => 'vagrant',
    'password'     => 'vagrant'
  }

  ActiveRecord::Base.establish_connection(config.merge('database' => 'postgres', 'schema_search_path' => 'public'))
  ActiveRecord::Base.connection.create_database(config['database'], config)
  ActiveRecord::Base.establish_connection(config)
  Foreigner.load

  ActiveRecord::Schema.define do
    create_table :dealers, :force => true do |t|
      t.integer :autosocial_group_id, null: true # null: false
      t.boolean :no_group, default: true
    end

    create_table :autosocial_groups, :force => true do |t|
    end

    add_foreign_key "dealers", "autosocial_groups", name: 'my_fk'
  end

  class Dealer < ActiveRecord::Base
    belongs_to :autosocial_group
  end

  class AutosocialGroup < ActiveRecord::Base
    has_many :dealers, dependent: :nullify
  end

  group  = AutosocialGroup.create
  dealer = Dealer.create(autosocial_group_id: group.id)

  puts Dealer.first.attributes

  group.destroy

  puts Dealer.first.attributes
ensure
  ActiveRecord::Base.establish_connection(config.merge('database' => 'postgres', 'schema_search_path' => 'public'))
  ActiveRecord::Base.connection.drop_database config['database']
end

ActiveRecord::Base.connection.execute("SELECT * FROM information_schema.columns WHERE table_schema = 'public'").map { |x| x['column_name'] }