On Fri, Sep 1, 2017 at 8:26 AM, Антонио Антуан <a.ch....@gmail.com> wrote:
> Hi guys.
> I have several questions and, possibly, misunderstandings about sqlalchemy
> connection pooling behavior
>
> 1. I try to figure out if this is normal:
> https://gist.github.com/aCLr/be78f3495892978ee868c9b5adcef0e6
>
> As you can see, I checked that `bind` is the same on `get_bind()` invokation
> and on attribute call.
> I see, that each connection into session binds only for session, not for
> bind...
> Is it correct? I expected that each connection is bound for `bind`
> (`engine`).
that's normal because your exception is when you try to execute
directly from the Engine.
this is equivalent:
engine = create_engine(conn_string,
poolclass=pool.AssertionPool)
conn = engine.connect()
conn.scalar("select 1") # ok
conn.execute("select 1").scalar() # ok
engine.execute("select 1") # not OK, the engine doesn't know about
your "conn", it checks out a new connection
>
> 2. Here is the problem, on which I started my research:
> https://gist.github.com/aCLr/b642c822b0bd3c9ec1fe775452479acd
> I don't use commit here, only flush. But I expected that results on each
> execution will be the same, because I used same bind on query compilation
> and on `Session.query...` execution.
>
> Yes, I've read about `reset_on_return` parameter of Pool.
right, there's some odd patterns here, but it is "reset_on_return"
that is ultimately hitting the rollback here.
The query is wrong too, needs a FROM:
_query =
Session.query(func.count(literal('*'))).select_from(Test).limit(1).statement.compile(bind=Session.bind,
dialect=Session.bind.dialect)
and the assertions need to use scalar():
assert (_query.scalar() == amount), 'failed on compiled query execution'
reset on return, as well as some nice debugging so you can see things happening:
engine = create_engine(conn_string,
poolclass=pool.StaticPool, echo='debug',
echo_pool='debug',
pool_reset_on_return=None)
And when I specify
> that parameter with `None` value, failed only first asserion ('failed on
> compiled query execution') because, as I think, another connection is used.
> My question is the same: isn't it wrong? And if it is, how can I avoid
> AsserionError on compiled query execution? Should I use private
> `_connection_for_bind` method of Session class or there are any other
> options?
>
>
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
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--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
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