Example of using active record without Rails

active_record_sqlite.rb

# Run `gem install active_record sqlite3` to install the dependencies

ENV['DATABASE_URL'] = 'sqlite3:/tmp/sqlite.test' # Change this to anything you want

require 'sqlite3' # Make sure to require the correct adapter for your `DATABASE_URL`
require 'active_record'

ActiveRecord::Base.establish_connection

ActiveRecord::Schema.define do
  create_table :users do |t|
    t.column :name, :string
    t.timestamps
  end

  create_table :posts do |t|
    t.column :user_id, :integer
    t.column :title, :string
    t.column :body, :text
    t.timestamps
  end
end

class User < ActiveRecord::Base
  has_many :post
end

class Post < ActiveRecord::Base
  belongs_to :user
end

# Example codes

User.count # => 0 (we don't have any record in table `users` yet)
user = User.create(name: "John")
User.count # => 1 (now we have one user, which is John)
user.destroy
User.count # => 0

# If you know that the table exists and you just want to quickly connect to it:
class User < ActiveRecord::Base
  establish_connection "sqlite3:/tmp/sqlite.test" # Change this to your database url
end
User.count # => 0