Home     |     .Net Programming    |     cSharp Home    |     Sql Server Home    |     Javascript / Client Side Development     |     Ajax Programming

Ruby on Rails Development     |     Perl Programming     |     C Programming Language     |     C++ Programming     |     IT Jobs

Python Programming Language     |     Laptop Suggestions?    |     TCL Scripting     |     Fortran Programming     |     Scheme Programming Language


 
 
Cervo Technologies
The Right Source to Outsource

MS Dynamics CRM 3.0

Ruby Programming Language

YAML and ruby classes


I need to create some objects of different (custom) classes, in
different pages of my site, so I made some code that takes an array of
hashes and create the objects. the hashes are like this one:

h = { :class => Class1, :param1 => 'foo', :param2 => 'bar', etc }

and basically I do

object = h[:class].new(h)

everything works fine as long as the hash is defined inside the source
code. however in some case I need to create the same object in two
different file. to avoid writing the same hashes twice I though about
putting them in a YAML file but this method doesn't work anymore because
the class name is converted to a string instead of a reference to the
class, using !ruby/object creates the object but all the code inside the
initialize method seems to be never executed (or the instance variables
ovverrided after the inzialize method) so my objects don't work,
ClassName.to_yaml returns an error, etc...

is there a way to do what I want to do? putting the ashes in a file and
loading them as a source AFAIK creates other problem due to the
sandboxing made by mod_ruby, that's why I tried with yaml.

--
Deh! Impiacciami, imploroti
sgabazzone rampante!

Tirsdag den 13. Marts 2007 skrev Matteo Cavalleri:

Object.const_get can convert a String to a constant, so if you do:

      Object.const_get(h[:class].to_s).new(h)

it should work, no matter if the hash comes from source or yaml

br. Chr.

On Mar 13, 2007, at 9:50 AM, Matteo Cavalleri wrote:

It seems to me this is a fundamental problem with YAML. Even if you  
were trying to put all the data in one file, I don't believe the YAML  
spec. addresses writing object references instead of objects. This is  
especially an issue when your objects have circular references.

This caused me to use XML instead of YAML for a recent Java project  
because the Java XStream library handles serializing and  
deserializing Java objects that have circular references.

If there is a YAML solution to this, I'd love to hear about it!

On Wed, 14 Mar 2007, Mark Volkmann wrote:

> It seems to me this is a fundamental problem with YAML. Even if you were
> trying to put all the data in one file, I don't believe the YAML spec.
> addresses writing object references instead of objects. This is especially an
> issue when your objects have circular references.

> This caused me to use XML instead of YAML for a recent Java project because
> the Java XStream library handles serializing and deserializing Java objects
> that have circular references.

> If there is a YAML solution to this, I'd love to hear about it!

harp:~ > ruby -r yaml -e'  h = {};  h[:h] = h;  y h  '
&id001
:h: *id001

regards.

-a
--
be kind whenever possible... it is always possible.
- the dalai lama

On Mar 13, 2007, at 10:28 AM, ara.t.how@noaa.gov wrote:

My apologies! Apparently the problem is with the Java implementation  
of YAML that I was using and not with YAML itself. Here's a more full  
example that demonstrates YAML doing the right thing with multiple  
references to the same object and with circular references.

---

require 'yaml'

class Person
   attr_accessor :name, :spouse, :address

   def to_s
     "\n#{name} is married to #{spouse.name} and lives at\n#{address}"
   end
end

class Address
   attr_accessor :street, :city, :state, :zip

   def to_s
     "#{street}\n#{city}, #{state}  #{zip}"
   end
end

a = Address.new
a.street = "644 Glen Summit"
a.city = "St. Charles"
a.state = "MO"
a.zip = 63304

p1 = Person.new
p1.name = "Mark Volkmann"
p1.address = a

p2 = Person.new
p2.name = "Tami Volkmann"
p2.address = a

p1.spouse = p2
p2.spouse = p1

people = [p1, p2]
yaml_string = YAML::dump(people)
puts yaml_string

new_people = YAML::load(yaml_string)
puts new_people

---

The output is

---
- &id002 !ruby/object:Person
   address: &id001 !ruby/object:Address
     city: St. Charles
     state: MO
     street: 644 Glen Summit
     zip: 63304
   name: Mark Volkmann
   spouse: &id003 !ruby/object:Person
     address: *id001
     name: Tami Volkmann
     spouse: *id002
- *id003

Mark Volkmann is married to Tami Volkmann and lives at
644 Glen Summit
St. Charles, MO  63304

Tami Volkmann is married to Mark Volkmann and lives at
644 Glen Summit
St. Charles, MO  63304

Christian Surlykke <christ@surlykke.dk> wrote:

> Object.const_get can convert a String to a constant, so if you do:

>       Object.const_get(h[:class].to_s).new(h)

> it should work, no matter if the hash comes from source or yaml

the idea was excellent but it seems it doens't work if the class I need
is defined in another class namespace, e.g.

irb(main):117:0> Object.const_get('CGI::Cookie')
NameError: wrong constant name CGI::Cookie

anyway thanks for the help

--
Deh! Impiacciami, imploroti
sgabazzone rampante!

Mark Volkmann <m@ociweb.com> wrote:
> This caused me to use XML instead of YAML for a recent Java project  

mh... if I don't find a solution with yaml I'll try xml with ruby.
thanks.

--
Deh! Impiacciami, imploroti
sgabazzone rampante!

If you reference the class object directly, you can't dump it to yaml, so
try using a string instead, and running eval on the string to get the
class object.

h = { :class => 'Class1', :param1 => 'foo', :param2 => 'bar', etc }
object = eval(h[:class]).new(h)

This gives you the following YAML:
---
:class: Class1
:param1: foo
:param2: bar

--
Ken Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/

Alle marted 13 marzo 2007, Matteo Cavalleri ha scritto:

> Christian Surlykke <christ@surlykke.dk> wrote:
> > Object.const_get can convert a String to a constant, so if you do:

> >       Object.const_get(h[:class].to_s).new(h)

> > it should work, no matter if the hash comes from source or yaml

> the idea was excellent but it seems it doens't work if the class I need
> is defined in another class namespace, e.g.

> irb(main):117:0> Object.const_get('CGI::Cookie')
> NameError: wrong constant name CGI::Cookie

> anyway thanks for the help

Can't you store the class name (using Class#name) instead of the class itself
in the yaml file? This way, since Class#name returns the full 'path',
including modules, you can then do something like:

name=h[:class]
name.split('::').inject(Object){|res, c| c.const_get(c)}.new h

(taken from the solutions of the ruby quiz 133
(http://www.rubyquiz.com/quiz113.html))

I hope this helps

Stefano

Ken Bloom <kbl@gmail.com> wrote:
> h = { :class => 'Class1', :param1 => 'foo', :param2 => 'bar', etc }
> object = eval(h[:class]).new(h)

it works! thanks :)

--
Deh! Impiacciami, imploroti
sgabazzone rampante!

Stefano Crocco <stefano.cro@alice.it> wrote:
> name.split('::').inject(Object){|res, c| c.const_get(c)}.new h

this is pretty complicated for my current knowledge of ruby :D the
method suggested by ken bloom works and is simpler for me, but thanks
anyway for you help! :)

--
Deh! Impiacciami, imploroti
sgabazzone rampante!

It is possible to extend YAML to serialize classes:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/177604

It seems to still work with ruby-1.8.6.

It lets you do this:

yy = [Enumerable, Comparable, String, File].to_yaml
puts yy
p YAML.load(yy)

with output:

---
- !ruby/module Enumerable
- !ruby/module Comparable
- !ruby/class String
- !ruby/class File
[Enumerable, Comparable, String, File]

However, if you are hand-editing the YAML file, you may find that a
class name string is more convenient than this notation.

YYAMLMMV

--
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

Joel VanderWerf <v@path.berkeley.edu> wrote:
> However, if you are hand-editing the YAML file, you may find that a
> class name string is more convenient than this notation.

I think i'll go for the class name string :) but thanks for the link to
the extension. as I'm still learning ruby it was very interesting.

--
Deh! Impiacciami, imploroti
sgabazzone rampante!

On Wed, Mar 14, 2007 at 01:25:06AM +0900, Matteo Cavalleri wrote:
> Stefano Crocco <stefano.cro@alice.it> wrote:

> > name.split('::').inject(Object){|res, c| c.const_get(c)}.new h

> this is pretty complicated for my current knowledge of ruby :D the
> method suggested by ken bloom works and is simpler for me, but thanks
> anyway for you help! :)

To get at Foo::Bar::Baz you need to do

    klass = Object.const_get("Foo").const_get("Bar").const_get("Baz")

So that one-liner above is really another way of writing:

name = "Foo::Bar::Baz"
names = name.split("::")
klass = Object
while n = names.shift
  klass = klass.const_get(n)
end

Add to del.icio.us | Digg this | Stumble it | Powered by Megasolutions Inc