[libdbi-devel] Re: [libdbi-users] stupid question about nulls

[Christian S. <chr...@ce...>]

Hmm yes, it was something like that I haved in mind .... 

But you are right. The unsigned'ness doesn't make this idea kosher. I didn't 
see that coming, my bad.
I guess it was when the unsigned'ness of  field_sizes got in, the problem  
with distinguish NULL fields got to the surface.

The right way to fix this problem might accually be to add an extra variable 
in dbi_row_t. And use that in dbi_result_field_isnull() to track down if a 
field is null or not.
That variable could be make into a bitfield in case there is some more 
meta-data that could be added to a column in the future. The drivers could 
then bitwise adding on values define in libdbi. say DBI_FIELD_ISNULL and 
more....


regards, 

//Christian 

On Friday 30 July 2004 11.52, m.e...@ls... wrote:
> Like this? This seems to work for me, but I find it vaguely troubling
> that the field size, which is an unsigned long long, is meant to be
> negative...
>
> dbd_pgsql.c.patch:
> 512a513
>
> >                       row->field_sizes[curfield] = -1;
>
> dbi_result.c.patch:
> 334a335,344
>
> > unsigned short dbi_result_isnull(dbi_result Result, const char*
>
> fieldname) {
>
> >       unsigned long long size = dbi_result_get_field_size(Result,
>
> fieldname);
>
> >       return (size == -1) ? 1 : 0;
> > }
> >
> > unsigned short dbi_result_isnull_idx(dbi_result Result, unsigned short
>
> idx) {
>
> >       unsigned long long size = dbi_result_get_field_size_idx(Result,
>
> idx);
>
> >       return (size == -1) ? 1 : 0;
> > }
>
> On Thu, 2004-07-29 at 17:43, Christian Stamgren wrote:
> > Hello again,
> >
> > Guess you are using the function
> > dbi_result_get_field_length( )   which today return size-1 for some
> > reason.
> >
> > You could use:
> > dbi_result_get_field_size( )  which returns the accual value.
> >
> > But I guess these functions would need to be tweaked to fit in with this
> > new behaviour.
> > The right (clean) way  of doing things would be to implement
> > dbi_result_field_isnull() or simular to check if a field is null.
> > That way we could change the internals of libdbi without changing all
> > applications that was hacked to check if size was -1. It will also make
> > it more obvious what happens.
> >
> > Regards,
> >
> > //Christian
> >
> > On Thursday 29 July 2004 15.14, m.e...@ls... wrote:
> > > Thanks Christian! I didn't even think of looking at the length...
> > >
> > > I only have pqsql, but it looks as if for this one at least the length
> > > is always 0 except for strings, where it is equal to the length of the
> > > string (as you say it does not seem to implement what's in the
> > > comment).
> > >
> > > I tried implementing your suggestion myself in dbd_pgsql.c, and got as
> > > far as
> > >
> > > 512a513
> > >
> > > >                       row->field_sizes[curfield] = -1;
> > >
> > > Unfortunately, now I get a length of -2 for NULLs???
> > >
> > > Maybe someone familiar with the driver could have a look at this? It
> > > would be neat to be able to distinguish between NULL, "" and 0...
> > >
> > > Max
> > >
> > > On Thu, 2004-07-29 at 12:41, Christian Stamgren wrote:
> > > > Hello.
> > > >
> > > > I belive this is a short comming of the libdbi-drivers as it looks
> > > > today.
> > > >
> > > > By reading dbi-dev.h you will find this row part of dbi_row_t
> > > > struct.:
> > > >
> > > > unsigned long long *field_sizes; /* NULL field = 0, string field =
> > > > len, anything else = -1 */
> > > >
> > > > But the drivers does not implemet it this way.
> > > >
> > > >
> > > > I'll suggest that we change it so that:
> > > > NULL field = -1, string field = len, anything else = 0
> > > >
> > > > That way we will have distinction between NULL and a string of 0
> > > > chars (which is not the same as NULL).
> > > >
> > > > It would then be easy to implement a couple of funtions like:
> > > >
> > > > dbi_result_field_isnull(result, "fieldname");
> > > > or
> > > > dbi_result_field_isnull_idx(result, 2);
> > > >
> > > >
> > > >
> > > > Regards,
> > > >
> > > > //Christian
> > > >
> > > > On Wednesday 28 July 2004 15.45, m.e...@ls... wrote:
> > > > > Hi,
> > > > >
> > > > > I have been running some queries that return NULLs at times (in
> > > > > fields that contain doubles).
> > > > >
> > > > > It looks as if you use dbi_result_get_double() you get 0 whenever
> > > > > the query returned a NULL.
> > > > >
> > > > > How can I distinguish between a NULL and 0? It looks like I might
> > > > > have missed something obvious here...
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Max
> > > > >
> > > > >
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