루비 메타프로그래밍, Part 3: 실전 메타프로그래밍

C:\>mysql -uroot -p
Enter password:
mysql> create database example_db default charset utf8;
Query OK, 1 row affected (0.44 sec)

C:\>gem install mysql
Bulk updating Gem source index for: http://gems.rubyforge.org
Successfully installed mysql-2.7.3-mswin32
Installing ri documentation for mysql-2.7.3-mswin32...
Installing RDoc documentation for mysql-2.7.3-mswin32...
While generating documentation for mysql-2.7.3-mswin32

C:\>irb --simple-prompt
>> require "mysql"
=> true
>> connection = Mysql.init
=> #<Mysql:0x2e85c7c>
>> connection.real_connect("localhost", "root", "", "example_db")
=> #<Mysql:0x2e85c7c>

mysql> use example_db;
Database changed
mysql> create table users (
    ->   id int not null auto_increment primary key,
    ->   name varchar(8) not null,
    ->   email varchar(60) not null,
    ->   created_at datetime not null
    -> );
Query OK, 0 rows affected (0.10 sec)

mysql> insert into users (name, email, created_at) values ("Chul-Soo Kim",
"chulsoo@hanmail.net", "2008-05-02 10:30:00"), ("Young-hui Lee",
"younghui@naver.com", "2008-05-10 14:25:00");

 

>> result = connection.query("select * from users")
=> #<Mysql::Result:0x110df50>
>> result.fetch_row
=> ["1", "Chul-Soo Kim", "chulsoo@hanmail.net", "2008-05-02 10:30:00"]
>> result.fetch_row
=> ["2", "Young-hui Lee", "younghui@naver.com", "2008-05-10 14:25:00"]

class User < Base
end

require 'mysql'

class Base
  attr_accessor :new_record

  class <<self
    attr_accessor :table_name, :attributes
  end

  def self.inherited(subclass)
    subclass.table_name = underscore(subclass.name) + "s"
    subclass.attributes = []

    result = query("desc #{subclass.table_name}")
    while (row = result.fetch_row)
      subclass.attributes << row[0]
      subclass.class_eval <<-EOS
        def #{row[0]}
          @#{row[0]}
        end
        def #{row[0]}=(value)
          @#{row[0]} = value
        end
      EOS
    end
  end

  def self.query(str)
    unless @connection
      @connection = Mysql.init
      @connection.options(Mysql::SET_CHARSET_NAME, "utf8")
      @connection.real_connect("localhost", "root", "", "example_db")
    end
    
    @connection.query(str)
  end

  def self.insert_id
    @connection.insert_id
  end

  def self.underscore(camel_cased_word)
    camel_cased_word.to_s.gsub(/([a-z])([A-Z])/, '\1_\2').downcase
  end

  def self.find(id)
    record = self.new
    record.new_record = false
  
    result = query("select * from #{@table_name} where id=#{id}")
    if (row = result.fetch_row)
      self.attributes.each_with_index do |a, i|
        record.send("#{a}=", row[i])
      end
    end
    record
  end

  def initialize(attributes={})
    self.new_record = true

    self.class.attributes.each do |a|
      self.send("#{a}=", nil)
    end
  end
  
  def save
    if self.new_record
      self.class.query("insert into #{self.class.table_name} " +
      "(#{self.class.attributes[1..-1].join(',')}) values " +
      "(#{self.class.attributes[1..-1].map {|a| self.send(a).inspect}.join(',')})")
      self.id = self.class.insert_id
    else
      self.class.query("update #{self.class.table_name} set " +
      "#{self.class.attributes[1..-1].map {|a| "#{a} = #{self.send(a).inspect}"}.join(',')} " +
      "where id=#{self.id}")
    end
    true
  end
end

>> load "base.rb"
=> true
>> load "user.rb"
=> true
>> u = User.find(2)
=> #<User:0x110457c @created_at="2008-05-10 14:25:00", @name="Young-Hui Lee", @new_record=false, @email="younghui@naver.com", @id="2">
>> u.name
=> "Young-Hui Lee"
>> u.email
=> "younghui@naver.com"

>> u = User.new
=> #<User:0x1106fac @created_at=nil, @name=nil, @new_record=true, @email=nil, @id=nil>
>> u.name = "Gildong"
=> "Gildong"
>> u.email = "gildong@gmail.com"
=> "gildong@gmail.com"
>> u.created_at = "2008-05-26 20:30:00"
=> "2008-05-26 20:30:00"
>> u.save
=> true