Re: [gnome-db] introspection issue

[Murray Cumming <murrayc murrayc com>]

On Sat, 2011-04-09 at 18:39 +0200, Vivien Malerba wrote:
> On 8 April 2011 22:12, Murray Cumming <murrayc murrayc com> wrote:
> > GObject+Introspection is working quite well for me now with libgda.
> > Thanks. I am glad that pygda is now obsolete, so it's one less module
> > for me to maintain.
> >
> > However, I'm getting an error when trying to get the values from the
> > DataModel with get_value_at(). For instance, this script
> > http://git.gnome.org/browse/pygda/tree/examples/gda/select.py?h=introspection
> > produces this error:
> >
> > Traceback (most recent call last):
> >  File "./select.py", line 61, in <module>
> >    main ()
> >  File "./select.py", line 57, in main
> >    print "        value=", data_model.get_value_at(col_index,
> > row_index);
> >  File "/opt/gnome230/lib/python2.7/site-packages/gi/types.py", line 44,
> > in function
> >    return info.invoke(*args)
> > TypeError: unknown type (null)
> >
> >
> > Presumably it doesn't like GdaValues with GType=0 (when
> > gda_value_is_null(gvalue) is true).
> 
> Yes, the a GValue with a 0 GType represents a SQL NULL value, whereas
> if the returned value is NULL (the C NULL) then it means there was an
> error retreiving the value, hence the difference between the 2.

Can we just ignore that meaning of C NULL? We might need to check that
everything throws a GError instead, but the GdaConnection functions
already do:
http://developer.gnome.org/libgda/unstable/GdaConnection.html#gda-connection-execute-select-command

Otherwise we would need to distinguish between a SQL Null value and a C
NULL value, which would be hard in Python unless we have a Gda.Null
class with a GDA_TYPE_NULL GType. I don't think it's worth it unless we
can't always use GError instead.

-- 
murrayc murrayc com
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