[Zope] ExtFile/ExtImage in Zope2 2.13 and Transaction Manager

[Jesus Cea]

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I did some tests a year ago about upgrading to 2.13.19. I use
ExtFile/ExtImage extensively and I had to patch it a bit.

I hit the problem that ExtFile tries to import "from Shared.DC.ZRDB.TM
import TM". Messing around a bit, I solved the issue installing
"Products.ZSQLMethods" product (via
<https://mail.zope.org/pipermail/zope/2012-January/176324.html>), but
this is not working with 2.13.21. I am getting tons of upgrade
warnings about zope packages.

The documentation for "Products/ExtFile/TM.py" says this:

"""
TMRegistry and ProxyTM

Use case
- --------

Persistent objects (ExtFiles) need to participate in ZODB transactions.
ExtFiles perform all operations using temporary files which are saved on
commit or deleted on abort.

Constraints
- -----------

- - TransactionManagers (TM) must not be persistent themselves, i.e. must
  not have a _p_jar attribute.

- - We have to make sure the ExtFile's _abort is called *before* the ZODB
  destroys the attributes of the persistent object.

Solution
- --------

- - ProxyTM is a subclass of TM.TM that keeps a (hard) reference to the
  (wrapped) persistent object it manages. Calls to _begin, _finish, and
  _abort are forwarded to the target object.

- - TMRegistry is a module-level container for ProxyTMs. It creates and
  holds ProxyTMs keyed by (target_id, thread_id).

- - ExtFiles implement _finish and _abort and register with the machinery
  by calling TM.register(self).

- - On commit (or abort) the ProxyTM notifies its target object and removes
  itself from the registry.

Hacks
- -----

- - We manipulate the transaction's _resources attribute directly. This is
  to guarantee the ProxyTM is processed before other resources. There may
  be a way to achieve this using official APIs only, but I can't seem to
  find one.

"""

How can I solve this?. Is there any product similar to
ExtFile/ExtImage? I can program Python if somebody guides me around
the zope2 internal details...

- -- 
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