ActiveRecord without Rails

activerecord_without_rails.rb

require 'active_record'
require 'sqlite3'

ActiveRecord::Base.establish_connection(
  :adapter => "sqlite3",
  :database  => "teachers.db"
)

# Migration
ActiveRecord::Schema.define do
  unless ActiveRecord::Base.connection.table_exists?(:teachers)
    create_table :teachers do |table|
      table.column :first_name, :string
      table.column :last_name, :string
      table.column :email, :string
      table.column :age, :integer
    end
  end
end

# Define model
class Teacher < ActiveRecord::Base
  validates :first_name, :last_name, :email, presence: true
end

# Seed data
Teacher.create(first_name: 'John', last_name: 'Doe', email:'john.doe@email.com', age: 33)
Teacher.create(first_name: 'Jane', last_name: 'Doe', email:'jane.doe@email.com', age: 34)