On Feb 26, 2010, at 8:50 AM, Chris Withers wrote:
> Michael Bayer wrote:
>> not sure if this is obvious, its the sqlite3.PARSE_DECLTYPES. The
>> SQLite date types don't expect this to be turned on. That is a
>> handy feature which I'm not sure was available in such a simple form
>> when I first wrote against the pysqlite dialect in Python 2.3.
>
> Indeed, the dates are the problem here. As we talked about at PyCon, the
> dates thing is a side effect of the thing my colleagues were trying to solve.
> I've attached a test case which demonstrates the problem.
ah sorry, didnt see the test case. you don't need SQLite converters for
this, you need a custom type for now until we fix that issue. ticket is
forthcoming.
>
> The test can be made to parse by adding the following:
>
> import sqlite3
> sqlite3.register_converter('NUMERIC',Decimal)
>
> ...and creating the engine as follows:
>
> engine = create_engine(
> "sqlite://",
> connect_args = {'detect_types':sqlite3.PARSE_DECLTYPES}
> )
>
> ..but then we have the problem that my original mail was about. Any other
> solutions or explanations on the truncating Decimals front?
>
>> A workaround is to use a "dummy" Date type that returns None for
>> bind_processor() and result_processor().
>
> Not gonna fly here, there's too many projects and developers this would touch
> :'(
>
>> I don't see any accessor on the SQLite connection that could tell us
>> if this flag is enabled. We don't want to do an isinstance()
>> because those are quite expensive.
>>
>
>> So what we can do here is utilize 0.6's "test the connection" trick,
>> to issue a "select current_timestamp()" from the SQLite connection,
>> and if it comes back as datetime we'd assume PARSE_DECLTYPES is on,
>> or at least some kind of date-based processor has been added. then
>> the SQLite date types would consult this flag. I added #1685 for
>> this which is tentatively targeted at 0.6.0 just so I dont lose
>> track of it.
>
> It sounds a bit icky, but I guess if there's no other way?
>
>> We might want to look into having 0.6 set a default handler for date
>> types in any case, would need to ensure its completely compatible
>> with what we're doing now.
>
> I dunno what this means...
>
>> Also not sure if you're aware, "pool_recycle" is not advisable with
>> a :memory: database. it would zap out your DB. sqlite also doesnt
>> require any "encoding" since it only accepts unicode strings - the
>> param is unused by SQLalchemy with sqlite.
>
> Yeah, both of these are there 'cos we swap out testing engine between MySQL
> and SQLite, I'll make sure they're only passed when we're really using
> MySQL...
>
> cheers,
>
> Chris
>
> --
> Simplistix - Content Management, Batch Processing & Python Consulting
> - http://www.simplistix.co.uk
> from sqlalchemy import create_engine
> from sqlalchemy.orm import sessionmaker
> from sqlalchemy.orm.session import Session
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.schema import Column
> from sqlalchemy.types import String, Numeric, Integer
>
> import unittest
> from decimal import Decimal
>
> class Test(unittest.TestCase):
>
> def test_truncate(self):
> # setup
> engine = create_engine("sqlite://")
> self.Session = sessionmaker(
> bind=engine,
> autoflush=True,
> autocommit=False
> )
> Base = declarative_base(bind=engine)
> class MyModel(Base):
> __tablename__ = 'test'
> id = Column(Integer, primary_key=True)
> value = Column(Numeric(precision=36,scale=12))
> Base.metadata.create_all()
> session = self.Session()
>
> # precision=36 scale=12 should mean this can handle 12 decimal places
> # and this has 12 decimal places.
> session.add(MyModel(value="152.737826714556"))
> session.commit()
>
> obj = session.query(MyModel).one()
>
> # this will fail with the output, it shouldn't
> # Decimal("152.737826715") != Decimal("152.737826714556")
> self.assertEqual(obj.value, Decimal("152.737826714556"))
> --
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