[mapguide-internals] Exception thrown on null values?

[Traian Stanev]

How do you know said future provider will implement IsNull() correctly so that you rely on it? The answer is that you can't guarantee anything about future providers -- it's the responsibility of whoever writes the provider to fix it. So penalizing existing providers because of hypothetical future providers doesn't make much sense.


Traian


> -----Original Message-----
> From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-
> internals-bounces at lists.osgeo.org] On Behalf Of Bruce Dechant
> Sent: Thursday, February 28, 2008 5:17 PM
> To: MapGuide Internals Mail List
> Subject: RE: [mapguide-internals] Exception thrown on null values?
>
> I agree the provider should be fixed, but what about new providers that
> come out.
> What if they are not as diligent in their implementation? Should the
> server not try to prevent a crash to safe guard this instead of just
> blindly trusting every provider to be perfect?
>
> Bruce
>
> -----Original Message-----
> From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-
> internals-bounces at lists.osgeo.org] On Behalf Of Traian Stanev
> Sent: Thursday, February 28, 2008 3:14 PM
> To: MapGuide Internals Mail List
> Subject: RE: [mapguide-internals] Exception thrown on null values?
>
>
> So it will penalize everybody, instead of fixing the provider in
> question to throw an exception when it should?
>
> Traian
>
> > -----Original Message-----
> > From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-
> > internals-bounces at lists.osgeo.org] On Behalf Of Bruce Dechant
> > Sent: Thursday, February 28, 2008 5:12 PM
> > To: MapGuide Internals Mail List
> > Subject: RE: [mapguide-internals] Exception thrown on null values?
> >
> > Yup, but like I said at the cost of stability. :)
> >
> > I would rather do the check then have the server crash.
> >
> > -----Original Message-----
> > From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-
> > internals-bounces at lists.osgeo.org] On Behalf Of Traian Stanev
> > Sent: Thursday, February 28, 2008 3:09 PM
> > To: MapGuide Internals Mail List
> > Subject: RE: [mapguide-internals] Exception thrown on null values?
> >
> >
> > Hmm... always doing an IsNull() for everything has an overhead as
> well
> > -- internally to the provider it may be equivalent to getting the
> > property twice. Once to check for null and another time to get the
> > property value.
> >
> > Traian
> >
> >
> >
> > > -----Original Message-----
> > > From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-
> > > internals-bounces at lists.osgeo.org] On Behalf Of Bruce Dechant
> > > Sent: Thursday, February 28, 2008 5:05 PM
> > > To: MapGuide Internals Mail List
> > > Subject: RE: [mapguide-internals] Exception thrown on null values?
> > >
> > > Jason,
> > >
> > > This is the expected behavior as Traian pointed out. This was
> changed
> > > from what it was before because now we do the IsNull() check
> > internally
> > > in the server on all GetXXX() APIs just in case the user "forgot"
> to
> > > call it. This was also done to prevent memory access violations
> when
> > > trying to call for example GetString() from a reader that has a
> NULL
> > > property value and the underlying provider tries to do the read
> > string
> > > and then crashes, by adding this check we have added some server
> > > stability.
> > >
> > > Not all providers are created equally. :)
> > >
> > > Thanks,
> > > Bruce
> > >
> > >
> > > -----Original Message-----
> > > From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-
> > > internals-bounces at lists.osgeo.org] On Behalf Of Jason Birch
> > > Sent: Thursday, February 28, 2008 2:48 PM
> > > To: MapGuide Internals Mail List
> > > Subject: RE: [mapguide-internals] Exception thrown on null values?
> > >
> > > Am I allowed to say "lame"?  :)  NULL is a perfectly valid value
> for
> > > most data types, and throwing an exception in this case adds a lot
> of
> > > additional processing that should not be required.
> > >
> > > I personally feel that this is a case where MapGuide could make
> > > application developers lives a lot easier and improve (slightly?)
> the
> > > performance of web-level apps by swallowing the exception and
> > returning
> > > NULL.
> > >
> > > Jason
> > >
> > > -----Original Message-----
> > > From: mapguide-internals-bounces at lists.osgeo.org
> > > [mailto:mapguide-internals-bounces at lists.osgeo.org] On Behalf Of
> > Traian
> > > Stanev
> > > Sent: Thursday, February 28, 2008 13:31
> > > To: 'MapGuide Internals Mail List'
> > > Subject: RE: [mapguide-internals] Exception thrown on null values?
> > >
> > > I think this complies with the FDO spec, which requires an
> exception
> > to
> > > be thrown when the value is null and you try to get it anyway. The
> > two
> > > solutions are to check for IsNull() before getting it, or to catch
> > the
> > > exception. The code *could* in theory return NULL in this case,
> > but...
> > >
> > > Traian
> > >
> > > > -----Original Message-----
> > > > From: mapguide-internals-bounces at lists.osgeo.org
> [mailto:mapguide-
> > > > internals-bounces at lists.osgeo.org] On Behalf Of Jason Birch
> > > > Sent: Thursday, February 28, 2008 4:29 PM
> > > > To: MapGuide Internals Mail List
> > > > Subject: [mapguide-internals] Exception thrown on null values?
> > > >
> > > > Hi,
> > > >
> > > > I'm seeing a case in MGOS 2.0 where MgFeatureReader->GetString()
> is
> > > > throwing an exception when the value of the string is null.
> > > >
> > > > Is this expected behaviour?  Has it changed since 1.2?  I believe
> > > that
> > > > I've seen a similar error in geometry, but don't have a test case
> > for
> > > > that yet.
> > > >
> > > > This is relatively easy to work around with a try/catch and
> > > suppressing
> > > > the error output if the message includes "null", but it's a bit
> > > > annoying.  Is there a better way of dealing with this?
> > > >
> > > > Jason
> > > > _______________________________________________
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