Simple ORM livecoding

orm.rb

class ORM

    def save
        if defined? @id
            sql_update
        else
            sql_insert
        end
    end

    def sql_insert
        # get names of all instance variables
        instance_vars = self.instance_variables.map { |iv| iv.to_s.sub('@', '') }
        # join them by commas into one string
        columns = instance_vars.join(', ')

        # get the values of all instance variables wrapped in quotes
        values = instance_vars.map { |iv| "'#{self.instance_variable_get("@#{iv}")}'" }
        values = values.join(', ')

        # generate table name from class name, lowercase and pluralized
        # (i mean, we could set it manually, but we'll just do it this way just cause)
        table = "#{self.class.name.downcase}s"

        sql = "INSERT INTO #{table} (#{columns}) VALUES (#{values})"
        # @id = execute(sql).return_id
        @id = 1
        sql
    end

    def sql_update
        table = "#{self.class.name.downcase}s"

        instance_vars = self.instance_variables.map { |iv| iv.to_s.sub('@', '') }
        
        # generate the assignment parts of the sql update statement and join them by commas
        assignments = instance_vars.map do |iv|
            value = self.instance_variable_get("@#{iv}")
            assignment = "#{iv}='#{value}'"
        end.join(', ')


        sql = "UPDATE #{table} SET #{assignments} WHERE id=#{@id}"
    end
end

class Hand < ORM
    attr_accessor :num_fingers, :nail_length
end

class User < ORM
    attr_accessor :username, :email, :gender

    def initialize(username, email)
        @username = username
        @email = email
        @gender = gender
    end
end

user = User.new("murat", "[email protected]")

puts user.sql_insert
# user.id => 1

user.username = "tarum"
user.email = "[email protected]"
puts user.sql_update


hand = Hand.new
hand.num_fingers = 4
hand.nail_length = "2mm"

# should produce insert statement
puts hand.save.inspect
hand.num_fingers = 5
# should produce update statement
puts hand.save.inspect