[Mailman-Developers] Experimental SQLAlchemy port available

[Barry Warsaw]

Hi Mailman Hackers!

I wanted to let you know about some very cool work that Abhilash Raj has been
doing, and to request your help to review and test it.

You might know that for a long time, Mailman 3's ORM (Object Relational
Mapper) layer was provided by Storm[1].  There were a lot of things to like
about Storm, especially because it was such a nice, thin layer over SQL so it
was very transparent to use and easy to debug.  It had some downsides though,
and as the project lost momentum, those downsides became more apparent.

These included lack of any Python 3 support, and bugs in the PostgreSQL
layer.  As I eventually want MM3 to be a Python 3 application, and it looked
like Storm would never be ported, I have for a while desperately wanted to
port MM3 to SQLAlchemy.  At one point early in the MM3 fork, it *was* using
SA, but I had some problems with that (details are lost, and unimportant) and
switched to Storm.  Now, I think it's clear that SA is the best ORM available
for Python, and it is Python 3 compatible[2].

Abhilash has done a fantastic port of the MM3 trunk to SA.  I have taken his
branch, fixed a few test failures, and cleaned up a few things.  But really,
all the credit goes to Abhilash for his great work.

I have not yet merged the SA branch into trunk, for a few reasons.  Abhilash
is investigating Alembic as the schema migration layer, and I have not had
time to test the branch against PostgreSQL.  I would also like to invite folks
who have deployed MM3 to give the branch some testing, especially to make sure
that the new SA-derived schema is compatible with the hand-written schema
used by Storm.

Adopting SA will mean a break in upgrade guarantees.  We won't provide
migrations from 3.0b4's schema to 3.0b5, which is why I want them to be
effectively compatible.  After 3.0b5 is released, we'll likely use Alembic to
manage any future schema changes.  While I'd rather not make this break, I'm
convinced that the SA community can handle all this much better than our
crufty pile of schema migration code.

If you are able, please test this branch:

$ bzr branch lp:~barry/mailman/abhilash

That's essentially the 3.0 trunk with Abhilash's branch merged in, and my test
fixes and clean ups on top of that.  I'd like to merge this to trunk,
definitely for 3.0b5, so let's say in the next week or so.

Let us know how it goes!

Cheers,
-Barry

[1] https://storm.canonical.com/

[2] We are very likely going to adopt Falcon as a replacement for restish.
The latter suffers the same problems as Storm; it's not Python 3 compatible,
and it is effectively unmaintained upstream.  Falcon is really great, and with
the following changes, it will easily support restish-style object-based
traversal.  Storm and restish are the last Python 2-only dependencies of MM3
core.

https://github.com/racker/falcon/pull/307
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