not_active_record.rb

require "connection_adapter"
require "active_model"

module NotActiveRecord
  class Base
    include ActiveModel::Validations

    @@connection = SqliteAdapter.new

    def initialize(attributes={})
      @attributes = attributes
    end

    def method_missing(name, *args)
      if self.class.columns.include?(name)
        @attributes[name]
      else
        super
      end
    end

    def self.find(id)
      find_by_sql("SELECT * FROM #{table_name} WHERE id = #{id.to_i} LIMIT 1").first
    end

    def self.all
      find_by_sql("SELECT * FROM #{table_name}")
    end

    def self.find_by_sql(sql)
      rows = @@connection.execute(sql)
      rows.map do |values| # [1, 'Marc']
        attributes = map_values_to_columns(values)
        new(attributes)
      end
    end

    def self.map_values_to_columns(values)
      Hash[columns.zip(values)]
    end

    def self.columns
      @@connection.columns(table_name)
    end

    def self.table_name
      name.downcase + 's' # "users"
    end
  end
end