[Zope] setting up a ZClass - base class of PropertyManager? plus weird gradual broken product messages

[Steve Spicklemire]

On Monday, April 22, 2002, at 09:39  PM, A M Thomas wrote:

> Thanks, Steve,
>
> I prefer PropertyManager to property sheets at the moment for a couple
> of reasons: 1) I don't have to "group" my properties, I don't have to
> remember what property is in what sheet, I don't have to use quite so
> long a command to update the properties, and

So.. only use a single propertysheet. Long command.. yeah... it's a long 
command. ;-)

> 2) If I create an instance
> of a ZClass with a propertysheet, it seems to always define the
> properties, and I want to inherit them from a parent object unless I
> specifically define them in the new object.  I may be missing something,
> but I seemed to get this effect, and that's why I switched to using
> PropertyManager.

Hmmm... the property sheet only gives the class a value for the named 
properties. This "class" value gets used if the instance doesn't have a 
value of it's own. You can give the class value some "special" value 
(e.g., 'uninitialized') if you want to check an instance to see if 
you've set a custom value for that instance.

>
> I understand why one would be nervous about ZClasses.  It is a pain not
> to be able to change base classes easily!  Deleting instances and
> starting over will probably not be an option in the future, though, as
> my product will be used in some live sites, but I may still have to make
> significant changes.
>

Too bad. ;-) If you *need* ZClasses for some reason, you can also make a 
Python base class, and subclass from that. Then you can change the base 
class of your Python class later quite easily. You could even make this 
Python class subclass from PropertyManager if you decide that's really 
what you're after.

good luck!
-steve

> Thanks hugely for the response!
> Am
>
> Steve Spicklemire wrote:
>>
>> Hi Am,
>>
>> ZClasses have "propertsheets" already.. so you shouldn't really need to
>> inherit from PropertyManager. Also.. changing ZClasses by deleting and
>> recreating is a sort of "last ditch" scenario and likely to cause
>> problems. You're probably better off deleting all your old instances 
>> and
>> starting over. This is one of the "major problems" with ZClasses that
>> makes so many developers nervous about them. Having said all that, I
>> still find them useful in conjunction with a product like ZPatterns 
>> that
>> permits you to keep the actual data/relations in SQL or LDAP or 
>> whatever.
>>
>> -steve
>>
>> On Saturday, April 20, 2002, at 03:52 PM, A M Thomas wrote:
>>
>>> Hello there, and thank you very much in advance for any help.
>>>
>>> I'm working on my Zope (2.5.0) product through the management 
>>> interface,
>>> and realized that if I just created a ZClass with base classes of
>>> ObjectManager and CatalogAware, I couldn't add properties to it :(  
>>> So,
>>> I went to re-create my ZClass - and discovered that PropertyManager
>>> isn't in the list of selectable base classes.  Why is this?  Is there
>>> some way I can inherit directly from PropertyManager?
>>>
>>> I went ahead and created it with an additional base class of
>>> DTMLDocument, since it's got PropertyManager as one of its base 
>>> classes,
>>> but this isn't what I really want -- in addition to being slightly
>>> inelegant, now the manage_findForm method doesn't appear in the
>>> available methods for creating Views.
>>>
>>> Must I create my product in Python only to get PropertyManager 
>>> cleanly?
>>> Would this even work?  And would converting be easy?
>>>
>>> Also, I noticed a curious effect: I re-created my ZClass by moving all
>>> the methods into a temp ZClass, renaming the add and addform methods,
>>> and saving out the Class ID, then deleting the ZClass and the 
>>> remaining
>>> constructor objects (Permission, and Factory).  Then I created a new
>>> ZClass with the same name as the old one, and put in the saved 
>>> ClassID,
>>> replaced the new Add and Addform methods with my original ones (by
>>> deleting the new ones and renaming the original ones back to their
>>> original names), and pasting in the methods again.
>>>
>>> However, old instances of this ZClass _gradually_ started showing
>>> "broken product" messages.  First one, then overnight, two more - and
>>> the first one didn't seem to change immediately.  They shouldn't be
>>> broken anyway, right?  Is there some known issue about deleting and
>>> re-creating ZClasses in a product?  To make matters even more
>>> interesting, now one of them isn't broken anymore.  Yes, I've 
>>> re-created
>>> this ZClass more than once today, and this isn't a good diagnostic
>>> report, I know, but I just wanted to know if anyone knew what might be
>>> going on based on similar past experience.
>>>
>>> Thanks,
>>> Am
>>>
>>>
>>>
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