Add class_factory parameter to DB and ZConfig class-factory option

[perrinjerome]

DB.__init__() opens a connection to verify the root object exists, and that connection is returned to the pool for future reuse. Connections capture the classFactory reference at creation time (in Connection.__init__ via ObjectReader), so setting db.classFactory after DB.__init__() does not apply to connections already in the pool.

This is a problem for Zope, which overrides DB.classFactory after construction to provide graceful handling of broken/uninstalled objects. The first connection handed out after startup may silently use the wrong class factory.

Add a class_factory parameter to DB.__init__() that is set before any connection is opened, and a corresponding class-factory option to the ZConfig database configuration schema. This allows frameworks like Zope to pass the class factory at construction time.

• I signed and returned the Zope Contributor Agreement, and received and accepted an invitation to join a team in the zopefoundation GitHub organization.
• I verified there aren't any other open pull requests for the same change.
• I followed the guidelines in Developer guidelines.
• I successfully ran code quality checks on my changes locally.
• I successfully ran tests on my changes locally.
• If needed, I added new tests for my changes.
• If needed, I added documentation for my changes.
• I included a change log entry in my commits.

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If your pull request closes an open issue, include the exact text below, immediately followed by the issue number. When your pull request gets merged, then that issue will close automatically.

It does not fully close but is related to #420

[perrinjerome]

Hello @dataflake and @icemac , I used "ask for review" on this pull request. The explanation of the problem is on the linked issue. If something is not clear I can explain more. Thanks !

[dataflake]

I have not looked at this because I simply do not have in-depth knowledge of this code or a use case where I would need it.

[dataflake]

It would make more sense if you asked people who actually know this code better.

[Copilot]

Pull request overview

This PR makes the database class factory configurable at DB construction time and via ZConfig, so pooled connections created during DB.__init__() consistently use the intended class resolver (important for Zope’s broken/uninstalled object handling).

Changes:

• Add class_factory parameter to ZODB.DB.DB.__init__() and apply it before opening any initial connection.
• Add class-factory option to the ZConfig <zodb> schema and wire it through to ZODB.DB(...).
• Add doctests validating the constructor parameter and ZConfig option plumbing.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/ZODB/DB.py	Adds class_factory parameter and sets classFactory before initial connection/root verification.
src/ZODB/config.py	Adds a ZConfig datatype (importable_name) and passes class_factory through when opening DB from config.
src/ZODB/component.xml	Extends the <zodb> schema with a class-factory key.
src/ZODB/tests/testDB.py	Adds doctest coverage for class_factory being applied to the pooled init connection.
src/ZODB/tests/testConfig.py	Adds doctest coverage for the new class-factory ZConfig option.
CHANGES.rst	Documents the new constructor parameter and ZConfig option for the upcoming release.

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[dataflake]

That's an excellent use case for Copilot review. I didn't even think about it because I never use AI.

[perrinjerome]

Thanks for the feedback and thanks for running Copilot. The review suggestions were OK, I think I have addressed them all.

Note that at a very high level, this pull request, together with zopefoundation/Zope#1290 just move one configuration from Zope to ZODB, because Zope was configuring it by a monkey patching that was not working anymore. I think that it's a "small, easy" change :) although it was a bit hard to figure out the bug that this was causing.

[dataflake]

I'll just say the changes look plausible to me.

[perrinjerome]

Thanks @dataflake

I just realized there is a potential compatibility issue: a new ZODB version including this change will be incompatible with the current Zope version: Zope would refuse to start with a ZConfig error, because Zope still registers the class_factory key, which is now also registered by ZODB.
The plan is to update Zope to stop registering it via zopefoundation/Zope#1290, but the only valid combinations are either both ZODB and Zope include the change, or neither does.

I think that's not really an issue, because the only supported versions for Zope are the versions listed in https://github.com/zopefoundation/Zope/blob/master/versions-prod.cfg , so we can have incompatible version during development.

If that's actually a problem, please let me know, otherwise I'm ready to click merge, but I would need a new ZODB release to continue with zopefoundation/Zope#1290

[dataflake]

Go ahead and merge, I'll do the release.

[perrinjerome]

Thanks a lot

[dataflake]

ZODB 6.3 is now published.