Add a connector for SQLAlchemy with Psycopg2

[elemoine]

This PR adds a connector for SQLAlchemy with Psycopg2. The goal is for synchronous applications that use SQLAlchemy (e.g. a Flask application with the Flask-SQLAlchemy extension) to use just one SQLAlchemy engine, so just one connection pool, thereby minimizing the number of connections opened against the PostgreSQL server.

It works like this:

from slqlalchemy import create_engine

from procrastinate import App
from procrastinate.contrib.sqlalchemy import SQLAlchemyPsycopg2Connector

engine = create_engine("postgresql+psycopg2://")

app = App(connector=SQLAlchemyPsycopg2Connector())
app.open(engine)

Closes #445

Successful PR Checklist:

• Tests
  • (not applicable?)
• Documentation
  • (not applicable?)

[ewjoachim]

Should this be in contrib ?

[elemoine]

Yes, could be. I have no problem with moving it to the contrib folder. But do we agree that it's just a folder change, and that contribs have nothing else specific?

[elemoine]

I moved the connector to the contrib.sqlalchemy module.

[ewjoachim]

woo, new syntax ?

[elemoine]

I think the previous syntax did not work.

[elemoine]

Proof is that we didn't have to use poetry install --extras django in the CI.

[ewjoachim]

oh. Damn :/

[elemoine]

@ewjoachim, we get the following in the codecov report, and I don't know what to do to fix the problem:

Current head 17c25ba differs from pull request most recent head 0d0f407. Consider uploading reports for the commit 0d0f407 to get more accurate results

Do you know what we can do about it?

[github-actions]

Coverage report

The coverage rate went from 99.0% to 100.0% ⬆️

The branch rate is 99.72999999999999%

100% of new lines are covered.

[elemoine]

This is ready for review again.

[ewjoachim]

The branch rate is 99.72999999999999%

Woops :D I'll have to fix that in the github action :D

[ewjoachim]

Can we rather change . at the top of the file to .[django,sqlalchemy] ?

[ewjoachim]

Me, Galaxy brain, makes a comment requesting a change, then merges immediately.

[elemoine]

Good point. I'll create a PR for that if you haven't done it already.

[ewjoachim]

Wow, I'm not used to having so many imports from a module they don't fit on a single line :D. Well pixel real estate is cheap and if Black wants to spend a bazillion lines, it may well.