ActiveRecordを単独で使用するサンプル

ar_standalone.rb

require "active_record"
require "faker"

ActiveRecord::Base.establish_connection(
   adapter: "postgresql",
   host:    "localhost",
   username: "username",
   password: "password",
   database: "sample_db"
)


class Posts < ActiveRecord::Base

end

10.times do |i|
   Posts.create(id: i+100, title: Faker::Lorem.word, body: Faker::Lorem.paragraph)
end

p Posts.count