From: Steve Litt <slitt@...>
Date: 2008-09-30T03:05:07+09:00
Subject: Accessing a YAML loaded object without the object's definition?

Hi all,

In Ruby, I have a fairly complex nested object structure that I serialize to a 
yaml file. Then, in another program, I read it into a varaible like this:

obj = YAML::load_file("myfile.yaml");

I can see all objects and names in obj within irb, but I can't access them 
individually. For instance, in the original native that created the yaml, 
there's this:

obj.customer.city

You cannot access that from the object read in with load_file. It creates an 
error condition.

What DOES work is:

obj = Purchase.new(nil, nil)
obj = YAML::load_file("myfile.yaml");

puts obj.customer.city

That prints "Apopka". 

A sample program is at the bottom of this email. As long as the classes are 
defined in the program, they can be accessed. But if an object is created via 
YAML::load_file(), I'm not able to access its data members.

Is there any way I can do it without including the class definition in the 
code?

Thanks

SteveT

Steve Litt
Recession Relief Package
http://www.recession-relief.US

############ SAMPLE PROGRAM ###################
#!/usr/bin/ruby -w

require "yaml"

class Address
	attr_accessor :street, :city, :state, :zip
	def initialize(street, city, state, zip)
		@street = street
		@city = city
		@state = state
		@zip=zip
	end
end

class Customer
	attr_accessor :fname, :lname, :address
	def initialize( fname, lname, address)
		@fname = fname
		@lname = lname
		@address = address
	end
end


class Item
	attr_accessor :quantity, :priceper, :name
	def initialize(name, quantity, priceper)
		@name = name
		@quantity = quantity
		@priceper = priceper
	end
end

class Purchase
	attr_accessor :customer
	attr_reader :amount
	attr_accessor :date
	attr_reader :items

	def initialize(customer, date)
		@customer = customer
		@amount = amount
		@date = date
		@items = Array.new()
	end
	def additem(item)
		@items.push(item)
	end
	def update_amount()
		@amount = 0
		@items.each do
			|item|
			@amount += (item.quantity.to_f * item.priceper.to_f)
		end
	end
end

#### MAIN ROUTINE
#### Load objects
address = Address.new(["121 Main Street", "Suite 
201"], "Apopka", "FL", "33333");

customer = Customer.new("Steve", "Litt", address)

purchase = Purchase.new(customer, "3/3/2033")
purchase.additem(Item.new("Widget", 1, 1.00));
purchase.additem(Item.new("Gadget", 2, 2.00));
purchase.additem(Item.new("Left handed smoke bender", 3, 3.00));
purchase.update_amount()

#### Write out YAML to junk.yaml
ouf = File.new("./junk.yaml", "w");
ouf.write(YAML::dump(purchase))
ouf.close()

#### WRITE REPORT
#### Read YAML file and load into Purchase object p
p=Purchase.new(nil, nil)
p=YAML::load_file("./junk.yaml");

#### Date and total
printf "Purchase on %s, total cost $%0.2f\n", p.date, p.amount

#### Customer data
printf "\nCUSTOMER DATA:\n"
printf "%s %s\n", p.customer.fname, p.customer.lname
p.customer.address.street.each {|i| puts i}
printf "%s, %s, %s\n", p.customer.address.city, p.customer.address.state, 
p.customer.address.zip 

#### Items
printf "\nITEMS PURCHASED\n"
printf "%30s %10s %10s %10s\n", "ITEM NAME", "QUANTITY", "@", "TOTAL"
p.items.each do
	|item|
	printf "%30s %10d %10.2f %10.2f\n", item.name, item.quantity, item.priceper, 
item.quantity * item.priceper

end
printf "%30s %10s %10s %10s\n", " ", " ", " ", "----------"
printf "%30s %10s %10s %10.2f\n", "TOTAL", " ", " ", p.amount

############ END OF SAMPLE PROGRAM ###################