[ZODB-Dev] Re: Coping with Class Changes

[Tres Seaver]

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Dieter Maurer wrote:
> Chris S wrote at 2006-9-3 15:40 -0400:
>> Is there a standard procedure for dealing with fundamental changes to
>> classes? For instance, how do you make a ZODB cope with a class being
>> renamed, or being placed in a different location? How will it know
>> that oldmod.myclass == newmod.myclass?
> 
> It does not.
> 
> You can use so called "module aliases" to partially cope
> with module relocation and "class aliases" to cope with class renaming.
> Otherwise, you have to use migration scripts that physically
> recreate the objects (and the references to it!) with the new classes.

As an example of "module aliases" (which Zope handles for its own
add-ons), you could do something like (untested)::

  # BBB for renamed module
  import new, sys
  oldmod = new.module('oldmod')
  oldmod.myclass = MyClass
  sys.modules['oldmod'] = oldmod

Class renames are simpler, often just adding the old name immediately
below the renamed class::

  class UsedToBeFoo:
      pass
  Foo = UsedToBeFoo  # BBB for renamed class


Tres.
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Tres Seaver          +1 202-558-7113          tseaver at palladion.com
Palladion Software   "Excellence by Design"    http://palladion.com
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