On Thu, 2006-05-18 at 21:02 +0100, Christopher Arndt wrote:
> Oleg Broytmann wrote:
> > On Thu, May 18, 2006 at 05:51:47PM +0100, Christopher Arndt wrote:
> >
> >>class MySelectResult:
> >> def __nonzero__(self):
> >> return self.count() > 0
> >>
> >>SQLObject.SelectResultsClass.__bases__ += (MySelectResult,)
> >>
> >>class Person(SQLObject):
> >> name = StringCol(alternateID=True, length=20)
> >> org = StringCol(length=100)
> >>
> >>if __name__ == '__main__':
> >> Person.createTable()
> >> u1 = Person(name="joe", org="doe.com")
> >> u2 = Person(name="alice", org="foo.com")
> >> u3 = Person(name="bob", org="foo.com")
> >>
> >> pl = Person.select(Person.q.org == 'foo.com')
> >> if pl:
> >> for p in pl:
> >> print p.name
> >> else:
> >> print "No records found."
> >
> >
> > You ran two query. Is it really neccessary? Why not just
>
> Ok, this probably not the best example. But sometimes you just want to
> access the first (or the last) item of the result set.
>
> res = Person.select(...)
> if res:
> return res[0].someAttr
> else:
> return some_default
If you're only getting 1 record the call to count() may actually be more
costly than selecting the record, so you should still avoid it. You
could probably do this a few ways, but catching the IndexError seems the
cleanest to me:
try:
res = Person.select()[0]
except IndexError:
return default
else:
return res.someAttr
It might save people confusion if bool(SelectResults) Just Worked(TM),
but I think the extra database trip will always be unnecessary.
--
Matt Good <[EMAIL PROTECTED]>
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