From sven.emtell at doremir.com  Tue May 10 13:52:58 2011
From: sven.emtell at doremir.com (Sven Emtell)
Date: Tue, 10 May 2011 15:52:58 +0200
Subject: [cl-store-devel] serialized class instance as document format
Message-ID: <82425AB0-607C-442F-93A2-D4E2AD659D0D@doremir.com>

Hi all
I am planning to use cl-store to save and load documents in an  
application that I am developing.
What I want to save is a serialized class instance using cl- 
store:store and then later be able to load it using cl-store:restore.  
What troubles me is that in future versions of my application, there  
may be new slots in the class. My tests reveal that such new slots end  
up being unbound when loading an old class instance (without the  
slot). Instead I would like it to have the new slot set to  
it's :initform value.
Is this possible?
Any thoughts on using a serialized class instance as document format?
Thanks!
Sven



From alex.mizrahi at gmail.com  Tue May 10 17:02:08 2011
From: alex.mizrahi at gmail.com (Alex Mizrahi)
Date: Tue, 10 May 2011 20:02:08 +0300
Subject: [cl-store-devel] serialized class instance as document format
References: <82425AB0-607C-442F-93A2-D4E2AD659D0D@doremir.com>
Message-ID: <7CD6F7AAB1B04AAEBA9CF3A96535908C@killer>

hello

      SE>  I am planning to use cl-store to save and load documents in an
      application that I am developing.
      What I want to save is a serialized class instance using cl-
      store:store and then later be able to load it using cl-store:restore.
      What troubles me is that in future versions of my application, there
      may be new slots in the class. My tests reveal that such new slots end
      up being unbound when loading an old class instance (without the
      slot). Instead I would like it to have the new slot set to
      it's :initform value.
      Is this possible?


I'm not sure about cl-store specific solution, but here's how you can
auto-initialize (on demand) any unbound slots:

(defclass my-persistent-object () ())

(defmethod slot-unbound (class (instance my-persistent-object) name)
  ;; when we've got unbound slot
  ;; try reinitializing it with initform via shared initialize
  (shared-initialize instance (list name))
  (if (slot-boundp instance name)
      ;; if it becomes bound, call slot-value once again.
      ;; (I hope it does not get into loop.)
      (slot-value instance name)
      ;; otherwise call next method which signals error
      (call-next-method)))

Then make my-persistent-object parent for all classes which need this
init-on-demand behaviour.

I never use unbound slots anywhere in a normal course of a program (I use
NIL if something does not exist), so this works fine.

Even if you use unbound slots it is unlikely that you actually want unbound
slot condition to be signalled... 




From sven.emtell at doremir.com  Tue May 10 17:37:32 2011
From: sven.emtell at doremir.com (Sven Emtell)
Date: Tue, 10 May 2011 19:37:32 +0200
Subject: [cl-store-devel] serialized class instance as document format
In-Reply-To: <7CD6F7AAB1B04AAEBA9CF3A96535908C@killer>
References: <82425AB0-607C-442F-93A2-D4E2AD659D0D@doremir.com>
	<7CD6F7AAB1B04AAEBA9CF3A96535908C@killer>
Message-ID: <4C3D7DAA-BD83-49B3-BD8E-19ACB98439E4@doremir.com>

Thanks Alex!
For me I think it suffices using "(shared-initialize <my-instance>  
t)", then all unbound slots will be nicely initialized with  
their :initform value. I didn't know how the initialization worked -  
thanks for pointing me in the right direction.
Thoughts on using a serialized class instance as document format,  
anyone?
/Sven


10 maj 2011 kl. 19.02 skrev Alex Mizrahi:

> hello
>
>      SE>  I am planning to use cl-store to save and load documents  
> in an
>      application that I am developing.
>      What I want to save is a serialized class instance using cl-
>      store:store and then later be able to load it using cl- 
> store:restore.
>      What troubles me is that in future versions of my application,  
> there
>      may be new slots in the class. My tests reveal that such new  
> slots end
>      up being unbound when loading an old class instance (without the
>      slot). Instead I would like it to have the new slot set to
>      it's :initform value.
>      Is this possible?
>
>
> I'm not sure about cl-store specific solution, but here's how you can
> auto-initialize (on demand) any unbound slots:
>
> (defclass my-persistent-object () ())
>
> (defmethod slot-unbound (class (instance my-persistent-object) name)
>  ;; when we've got unbound slot
>  ;; try reinitializing it with initform via shared initialize
>  (shared-initialize instance (list name))
>  (if (slot-boundp instance name)
>      ;; if it becomes bound, call slot-value once again.
>      ;; (I hope it does not get into loop.)
>      (slot-value instance name)
>      ;; otherwise call next method which signals error
>      (call-next-method)))
>
> Then make my-persistent-object parent for all classes which need this
> init-on-demand behaviour.
>
> I never use unbound slots anywhere in a normal course of a program  
> (I use
> NIL if something does not exist), so this works fine.
>
> Even if you use unbound slots it is unlikely that you actually want  
> unbound
> slot condition to be signalled...
>
>
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