[Zope] Altering product instance changes all instances!

[Kevin Dangoor]

D'oh!

    This is actually a HOWTO that I meant to write 3 or 4 weeks ago.

    You can check out KM|Net News. My constructor clones DTML Methods
(instead of Images), but it was pretty easy and works completely within
DTML. I also added a "Defaults" tab so that you can easily plug the latest
"default" version into an individual instance.


Here is Albert Kinderman's summary of our discussion from October 1.

[quote]
In your xProduct, create a DTML document (or method) with id default.
This is at the same level as the xClass, xClass_add, xClass_addForm, and
xClassFactory.

[NOTE:  Kevin says to put the default in the xClass.  Try it either
way.]

In your xClass_add, include within the

<dtml-with "xClass.createInObjectManager(REQUEST['id'], REQUEST)">

the lines

<dtml-call "REQUEST.set('data',default.document_src(REQUEST,RESPONSE))">
<dtml-call "manage_addDTMLDocument('default','',data)">
[changed in the obvious way for a DTML Method]

along with any property sheet management call (as explained in the
comment in the standard xClass_add).

Now when you create an instance of x, the document default will be
automatically created within the instance created.  Since default is
inside of the instance, I believe you must have ZObjectManager as one of
the base classes. [I haven't tried it without ZObjectManager as a base
class, but I know it works when you do.]
[end quote]

Kevin

-----Original Message-----
From: Edd Dumbill <edd@usefulinc.com>
To: Michel Pelletier <michel@digicool.com>
Cc: Edd Dumbill <edd@usefulinc.com>; zope@zope.org <zope@zope.org>
Date: Monday, November 01, 1999 12:54 PM
Subject: Re: [Zope] Altering product instance changes all instances!


>On Mon, Nov 01, 1999 at 11:52:20AM -0500, Michel Pelletier wrote:
>> Edd Dumbill wrote:
>> >
>> > Hi
>> >
>> > For my SiteSummary [1] product, I have a default image that is stored
as a
>> > subobject in my ZClass.
>> >
>> > An instance of the product can upload a new image to replace it.
>> >
>> > Unfortunately that ends up replacing the image in _all_ instances of
the
>> > product.
>> >
>> > This is not the desired behavior!
>>
>> But it is probably the correcy behavior.
>
>Yes, I figured so
>
>> It sounds like maybe you want your object to be an ObjectManager, and
>> contain your Image.
>
>My object subclasses ObjectManager already.  The only way I figure to
>get round this is to add to the constructor some code which clones the
>Image in the class and adds it to the object itself.  I am dubious as to
>whether I can achieve this in DTML -- it's looking like I need an
>external method to achieve it.
>
>> I suppose the 'right' thing would be for each
>> instance to set an instance attribute when they are instanciated, but
>> you can't do that, because you can't set attributes from DTML, it would
>> violate security.  You *can* do it from an external method, but that
>> might be hairy..hmm.
>
>The 'right' thing happens to properties.  What I guess I wanted was to
>be able to add objects in as properties.  But of course this is only
>possible for a ZClass that subclasses ObjectManager, so there won't be
>anything in the existing Zope interfaces to enable me to do that.
>
>> You might be stretching ZClasses farther than they are capable of going,
>> at this point.
>
>:-) I think I might.
>
>>  It might be desireable for us to come up with some way
>> for instances to change their attributes, but this is typically not done
>> from DTML, DTML is expressly designed not to allow you to 'change'
>> objects without using a specific API that that object provides, in
>> Python, for the DTML programmer.
>
>I can conceive of a need for ZClasses which subclass ObjectManager to
>come "pre-loaded" with objects, kind of like a default population. As I
>said above, I guess I can achieve this by putting them in the class and
>then cloning them as part of the constructor.
>
>> -Michel
>
>Thanks for your very helpful response.  I'll now look into getting my
>constructor to do some cloning.
>
>-- Edd
>
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