[ZODB-Dev] Migration of obsolete BTrees to ZOPE 2.8

[Dieter Maurer]

Tim Peters wrote at 2005-11-18 10:02 -0500:
>[Margie Watkins CONT]
>> The issue http://www.zope.org/Collectors/Zope/1695 asks for a statement
>> from users who are affected by the missing modules.
>
>Unfortunately, that's become "out of sight, out of mind" since then -- the
>issue was opened 9 months ago, and to date you're the first to say you
>really need this (if you read through all the referenced threads, you'll see
>that everyone else who thought they _might_ need it eventually discovered
>that they did not).

It is no problem as long as you migrate while you are still
using a Zope 2.7 (ZODB 3.2) release.

We added automatic migration code to our old "BTree/Intset" using code.
But we may need an explicit conversion before we finally upgrade
to Zope 2.8 -- to get very rarely used objects upgraded as well.

> ...
>I'm not sure to what that refers, but not sure it matters either.  There are
>four threads referenced in the bug report, and AFAICT none of them claim to
>present a migration method for "old" BTrees or intSets.

The migration is trivial as long as "BTree" and "Intset" are still
available. We use for example the following "BTree" migration.

# backward (pre Zope 2.8) compatibility
try:
  from BTree import BTree as _BTreeOld
# DM 2005-08-25: for unknown reasons, this can raise an "AttributeError"
#  rather than an "ImportError"
#except ImportError: _BTreeOld = None
except (ImportError, AttributeError): _BTreeOld = None
from BTrees.OOBTree import OOBTree as BTree

	...
        tree = self._tree
        if _BTreeOld is not None and isinstance(tree, _BTreeOld):
            # still an oldy -- upgrade to modern structure
            self._tree = BTree(tree)
            msg = 'BTree upgraded'
        else: msg = 'BTree was already modern'

-- 
Dieter