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comp.lang.ruby

YAML and ruby classes

shiva.brahma

3/13/2007 2:47:00 PM

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!
15 Answers

Christian Surlykke

3/13/2007 3:13:00 PM

0

Tirsdag den 13. Marts 2007 skrev Matteo Cavalleri:
> 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.

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.

R. Mark Volkmann

3/13/2007 3:19:00 PM

0

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

> 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.

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!

Ara.T.Howard

3/13/2007 3:28:00 PM

0

R. Mark Volkmann

3/13/2007 3:45:00 PM

0

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

> 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

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

shiva.brahma

3/13/2007 3:51:00 PM

0

Mark Volkmann <mark@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!

shiva.brahma

3/13/2007 3:51:00 PM

0

Christian Surlykke <christian@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!

Ken Bloom

3/13/2007 4:08:00 PM

0

On Tue, 13 Mar 2007 15:47:13 +0100, Matteo Cavalleri wrote:

> 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.

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...

Stefano Crocco

3/13/2007 4:11:00 PM

0

Alle martedì 13 marzo 2007, Matteo Cavalleri ha scritto:
> Christian Surlykke <christian@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/qu...))

I hope this helps

Stefano

shiva.brahma

3/13/2007 4:22:00 PM

0

Ken Bloom <kbloom@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!

shiva.brahma

3/13/2007 4:22:00 PM

0

Stefano Crocco <stefano.crocco@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!