From: Robert Klemme <shortcutter@...>
Date: 2013-03-07T01:33:08+09:00
Subject: Re: Persisting and loading objects trhough Marshal problem

On Wed, Mar 6, 2013 at 4:58 PM, Damián M. González <lists@ruby-forum.com> wrote:
> Good question. See, I marshal them in differents times. Because I don't
> have to persist lot of information I don't use any database like MySQL,
> I just save the object in binary files(by marshaling). The application
> have a GUI, so when a user do some thing certain object is persisted,
> that object is pointing to other objects, like the example of @var_b.
> The problem is that when I regenerate the objects, the shown above
> happen.
>  When in some part of the source code I have to compare in the way above
> the are not equals:
>
>  b.var_b.inspect
>  #=> <A:0x0145A4>
>  a.inspect
>  #=> <A:0x457D78>
>
>  They are not the same, perhaps(meaby an obvious thing) because Marshal
> reconstruct the object just by looking their atributes saved but Marshal
> doesn't bother about create the same object that another that will be
> created with the same attributes. Am I right?

Marshal retains an idea of identity only during _one_ write operation.
 So it will reconstruct graphs properly if you ensure all interesting
instances are referenced from a single instance.

As Hans said: do it in one step for example by placing both in an Array:

irb(main):016:0> x, y = Marshal.load(Marshal.dump([a,b]))
=> [#<A:0x802ba284 @var_a=50>, #<B:0x802ba248 @var_b=#<A:0x802ba284 @var_a=50>>]
irb(main):017:0> x.equal? y.var_b
=> true

In your case it would also be sufficient to only marshal b because
that references a already and there is an easy way to access it after
deserialization.

Kind regards

robert

-- 
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