Possibly use SQLAlchemy Strategies

[dstufft]

It looks like the aiopg.sa module relies on reimplementing some of the lower level parts of SQLAlchemy and providing alternatives which use a similar API. I wonder if this could instead be done using SQLAlchemy's support for different execution strategies?

There is an example of doing this for Twisted at https://github.com/alex/alchimia, that defers things to a thread pool, largely because it wants to work for any database not just PostgreSQL. However I wonder if it would be possible to do that instead which might deduplicate some of the code?

[asvetlov]

Thank you for link to very interesting project.

I need to dig into alchimia code before making answer.

[dstufft]

Of course! I could be totally wrong too and the strategy thing might not be useful at all, but figured I'd mention it in case it was useful.

[jettify]

@dstufft interesting point

As far as I can see: sa.Connection, sa.Transaction (nested and two phase), sa.ResultProxy and sa.Engine must be implemented in both approaches, so there are not much savings.

But I think it would be interesting to add AIOPG_STRATEGY so end user can write something like:

from sqlalchemy import engine
from aiopg import  AIOPG_STRATEGY
@asyncio.coroutine
def go()
    engine = yield from create_engine(host, port, strategy=AIOPG_STRATEGY )

in this case DefaultEngineStrategy.create method must be reimplemented:
[1] https://github.com/zzzeek/sqlalchemy/blob/master/lib/sqlalchemy/engine/strategies.py#L47-L160

[dstufft]

By they way, here's some info:

https://twitter.com/zzzeek/status/559747418397634561
https://twitter.com/zzzeek/status/559747644088942592
https://twitter.com/zzzeek/status/559747756563378177

[eirnym]

@jettify You can't mix simple function call, generator and async def from Python3.5, so you must rewrite SQLAlchemy to use it in async mode.

[jettify]

@eirnym My point was not to rewrite SQLAlchemy, but use create_engine from sqlalchemy (not aiopg) in order to create instance of aiopg.Engine. This is kind of gives user common interface for engine creation.

But now I do not think this is good idea any more.

[RazerM]

I created a strategy for asyncio at https://github.com/RazerM/sqlalchemy_aio, based on alchimia.
It's currently a proof of concept (lacks tests and documentation).