Comment 8 for bug 143241

For the reference: wendelin.core also needs to preserve ._v_* attributes to not go away automatically during transaction. And to do so it adds LivePersistent class, which is just a Persistent with deactivated "_p_deactivate":

https://lab.nexedi.com/nexedi/wendelin.core/blob/a702d410/lib/zodb.py#L88-109
https://lab.nexedi.com/nexedi/wendelin.core/blob/a702d410/bigfile/file_zodb.py#L484-500
https://lab.nexedi.com/nexedi/wendelin.core/blob/a702d410/lib/tests/test_zodb.py#L53-183