[Zope-dev] Product upgrades

[Steve Alexander]

...and, this is a good argument for hiding the data in your objects' 
attributes, and only accessing that data through method calls. 
Encapsulation and data hiding.


Chris McDonough wrote:
> You either need to account for older-state objects in your code or you need
> to manually upgrade instances of your objects.  There's no standard way to
> do the latter.
> 
> ----- Original Message -----
> From: "brian.r.brinegar.1" <brinegar@purdue.edu>
> To: <zope-dev@zope.org>
> Sent: Tuesday, January 22, 2002 5:37 PM
> Subject: [Zope-dev] Product upgrades
> 
> 
> 
>>I have done work on a couple of products and one thing I've noticed is if
>>you change what is done in the __init__ method of an object there isn't a
>>good way to make the change so that it takes effect on old instances of
>>the object. For example:
>>
>>def init(self):
>>self.data.append('cow')
>>
>>becomes:
>>
>>def init(self):
>>self.data.append('cow')
>>self.data.append('horse')
>>
>>things created with the first constructor must be removed and recreated if
>>'horse' is to be added. Is there a way to go through and update old
>>instances of a product to a newer version? Or should backwards
>>compatibility be designed into the product?
>>
>>Thanks,
>>--Brian

--
Steve Alexander