On Dec 28, 12:07 pm, Michael Bayer mike...@zzzcomputing.com wrote:
On Dec 28, 2011, at 11:34 AM, Kent wrote:
Was it your intention to no longer allow this type of query().get()?
session.query(cls.orderid).get(orderid)
it was ! yes.
I get InvalidRequestError: get() can only be used against a single mapped
class. but the wording is such that I'm not sure you intended to limit
that use case (there is only a single mapped class in that query).
From the POV of that message there's just a Column, and no mapped class,
actually being passed. I knew this wouldn't necessarily be very clear but
there was no better message I could think of.
I'll change such queries, just wanted to bring it up to see if you intended
it that way.
(Admittedly, if I recall correctly, when I first added it, I think I was
slightly surprised it worked as I expected...)
amazingly it took me just one second to find the originating issue, which was
that the identity map was still being searched, thereby causing the wrong
result:
http://www.sqlalchemy.org/trac/ticket/2144
I suspected that subsequent .get() invocations would return just the
column instead of the object, is that what was happening?
When something is used in a way I didn't anticipate, my first instinct is
often to first make that unanticipated case raise an error. That means it's
covered and people won't do it. Later, if we decide it should do something,
that can be re-introduced. It's always easier to unlock a dead end with a
well thought out approach, than to make multiple, small modifications to an
existing behavior.
That is the right approach, I'm convinced. I always feel I'm fighting
an eternal battle at work against the other guys' mindset of make the
program not crash if something unexpected happens, so at least there
is a chance it will keep running... Can't stand it. Things like
try: catch Exception: pass. ! It's far better to blow up before
doing damage, even if that damage is only speculative because it
wasn't used in the designed use case. Later, when that case comes up
you can analyze it and open the dead end, agreed.
Thanks, I've certainly got no issues with the semantics of get()
meaning get the instance.
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