01_enable_uuid_extension.rb

class EnableUuidExtension < ActiveRecord::Migration
  def up
    execute %Q{CREATE EXTENSION "uuid-ossp"}
  end

  def down
    execute %Q{DROP EXTENSION "uuid-ossp"}
  end
end

02_create_update_trigger.rb

class CreateUpdateTrigger < ActiveRecord::Migration
  def up
    execute <<-SQL
CREATE FUNCTION update_modified_column() RETURNS trigger
    LANGUAGE plpgsql
    AS $$
BEGIN
    NEW.updated_at = now();
    RETURN NEW;
END;
$$;
SQL
  end

  def down
    execute %Q{DROP FUNCTION update_modified_column}
  end
end

03_create_users.rb

class CreateUsers < ActiveRecord::Migration
  def up
    execute <<-SQL
CREATE TABLE "users" (
  "id"                      UUID NOT NULL DEFAULT uuid_generate_v4(),
  "email"                   CHARACTER VARYING DEFAULT ''::CHARACTER VARYING NOT NULL,
  "encrypted_password"      CHARACTER VARYING DEFAULT ''::CHARACTER VARYING NOT NULL,
  "reset_password_token"    CHARACTER VARYING,
  "reset_password_sent_at"  TIMESTAMP WITHOUT TIME ZONE,
  "remember_created_at"     TIMESTAMP WITHOUT TIME ZONE,
  "sign_in_count"           INTEGER DEFAULT 0 NOT NULL,
  "current_sign_in_at"      TIMESTAMP WITHOUT TIME ZONE,
  "last_sign_in_at"         TIMESTAMP WITHOUT TIME ZONE,
  "current_sign_in_ip"      INET,
  "last_sign_in_ip"         INET,
  "confirmation_token"      CHARACTER VARYING,
  "confirmed_at"            TIMESTAMP WITHOUT TIME ZONE,
  "confirmation_sent_at"    TIMESTAMP WITHOUT TIME ZONE,
  "unconfirmed_email"       CHARACTER VARYING,
  "failed_attempts"         INTEGER DEFAULT 0 NOT NULL,
  "unlock_token"            CHARACTER VARYING,
  "locked_at"               TIMESTAMP WITHOUT TIME ZONE,
  "created_at"              TIMESTAMP NOT NULL DEFAULT now(),
  "updated_at"              TIMESTAMP NOT NULL DEFAULT now(),
  PRIMARY KEY ("id"),
  UNIQUE("email"),
  UNIQUE("confirmation_token"),
  UNIQUE("unlock_token")
)
SQL

    execute <<-SQL
CREATE TRIGGER "update_users_updated_at"
  BEFORE UPDATE ON "users"
  FOR EACH ROW
  EXECUTE PROCEDURE update_modified_column()
SQL
  end

  def down
    execute %Q{DROP TRIGGER "update_users_updated_at" ON "users"}
    execute %Q{DROP TABLE "users"}
  end
end

active_record.rb

# config/initializers/active_record
ActiveRecord::Base.record_timestamps = false
ActiveRecord::Base.inheritance_column = :_type_disabled