From: Thufir <hawat.thufir@...>
Date: 2007-12-22T19:32:02+09:00
Subject: inheritance with ORM (ActiveRecord)

Maybe this is for the rails group since it involves ActiveRecord?  In any 
event, I have a db with a single table holding some Creature objects.  
When the Creature objects are instantiated, they're actually Dragons 
(which inherit from Creature, of course).

How is their inheritance reflected in the db?


thufir@arrakis ~/Desktop/dwemthys $ 
thufir@arrakis ~/Desktop/dwemthys $ ruby creatures.rb 
-- create_table(:creatures)
  SQL (0.011286)   CREATE TABLE creatures ("id" INTEGER PRIMARY KEY NOT 
NULL, "life" integer DEFAULT NULL, "strength" integer DEFAULT NULL, 
"charisma" integer DEFAULT NULL, "weapon" integer DEFAULT NULL) 
   -> 0.1332s
#<Dragon:0xb773f818 @new_record=true, @attributes={"strength"=>0, 
"charisma"=>0, "weapon"=>0, "life"=>0}>
  SQL (0.000884)   INSERT INTO creatures ("strength", "charisma", "life", 
"weapon") VALUES(0, 0, 0, 0)
#<Dragon:0xb773735c @new_record=true, @attributes={"strength"=>0, 
"charisma"=>0, "weapon"=>0, "life"=>0}>
  SQL (0.000948)   INSERT INTO creatures ("strength", "charisma", "life", 
"weapon") VALUES(0, 0, 0, 0)
#<Dragon:0xb7734184 @new_record=true, @attributes={"strength"=>0, 
"charisma"=>0, "weapon"=>0, "life"=>0}>
  SQL (0.000686)   INSERT INTO creatures ("strength", "charisma", "life", 
"weapon") VALUES(0, 0, 0, 0)
#<Dragon:0xb7732780 @new_record=true, @attributes={"strength"=>0, 
"charisma"=>0, "weapon"=>0, "life"=>0}>
  SQL (0.000703)   INSERT INTO creatures ("strength", "charisma", "life", 
"weapon") VALUES(0, 0, 0, 0)
#<Dragon:0xb7730318 @new_record=true, @attributes={"strength"=>0, 
"charisma"=>0, "weapon"=>0, "life"=>0}>
  SQL (0.000700)   INSERT INTO creatures ("strength", "charisma", "life", 
"weapon") VALUES(0, 0, 0, 0)
thufir@arrakis ~/Desktop/dwemthys $ 
thufir@arrakis ~/Desktop/dwemthys $ 
thufir@arrakis ~/Desktop/dwemthys $ cat creatures.rb 
require 'fileutils'
require 'active_record'
require 'Creature'
require 'Dragon'
 
system("rm dwemthys.db")
 
 
ActiveRecord::Base.logger = Logger.new(STDERR)
ActiveRecord::Base.colorize_logging = true
 
ActiveRecord::Base.establish_connection(
    :adapter => "sqlite3",
    :dbfile  => "dwemthys.db"
)
 
ActiveRecord::Schema.define do
    create_table :creatures do |table|
        table.column :life,             :integer
        table.column :strength,         :integer
        table.column :charisma,         :integer
        table.column :weapon,           :integer
    end
end
 
 
5.times {
        creature = Dragon.new
        p creature
        creature.save
}
thufir@arrakis ~/Desktop/dwemthys $ 
thufir@arrakis ~/Desktop/dwemthys $ cat Creature.rb 
require 'active_record'
 
class Creature < ActiveRecord::Base
 
attr_accessor :life, :strength, :charisma, :weapon
 
def to_s ()
        print "class\t\t"
        print self.class
 
        print "\nlife\t\t"
        print @life
 
        print "\nstrength\t"
        print @strength
 
        print "\ncharisma\t"
        print @charisma
 
        print "\nweapon\t\t"
        print @weapon
        print "\n"
end
 
 
end
thufir@arrakis ~/Desktop/dwemthys $ 
thufir@arrakis ~/Desktop/dwemthys $ cat Dragon.rb 
require 'Creature'
 
class Dragon < Creature
 
 
end
thufir@arrakis ~/Desktop/dwemthys $ 
thufir@arrakis ~/Desktop/dwemthys $


thanks,

Thufir