FreeTDS Development Group

["Thompson, Bill D (London)" <ThompBil AT exchange.uk.ml.com>]

Brian,

Im dealing with this in the API layer. It's pretty straightforward.

For example in the manual page for cs_convert it says :
srcdata - A pointer to the source data. To indicate that the source data
represents a null value, pass srcdata as NULL. If srcdata is NULL,
cs_convert places the null substitution value for the datatype indicated by
destfmt®datatype in *destdata. 
Table 2-14 lists the default null substitution value for each datatype. An
application can define custom null substitution values by calling cs_setnull
So thats pretty much what I've done ( I've left out the cs_null bit - shit,
those guys thought of everything...)
I'm also dealing with "like to like" conversions in the API layer. No need
to call tds_convert for those....
Bill



> -----Original Message-----
> From: Brian Bruns [SMTP:camber AT ais.org]
> Sent: Thursday, July 11, 2002 3:47 PM
> To:   TDS Development Group
> Subject:      [freetds] RE: Bug converting NULL field in SQLBindCol?
> 
> Bill,
> 
> Have you decided which approach you are taking on this? NULL handling
> brings up another condition, we've never expected the conversion routines
> to be responsible for it, the API's differ quite a bit on this issue.
> 
> Brian
> 
> > Small world!
> > 
> > I am actually in the process of doing a rework on the convert
> functionality
> > in FreeTDS.
> > There are a number of shortfalls in this, of which you've just spotted
> one.
> > I spotted the same issue as I was going through the code a couple hours
> ago!
> > 
> > have patience and it will be fixed....
> > 
> > Bill
> > 
> > > -----Original Message-----
> > > From:     Paul Rensing [SMTP:paul.rensing AT att.net]
> > > Sent:     Thursday, July 11, 2002 2:46 PM
> > > To:       TDS Development Group
> > > Subject:  [freetds] Bug converting NULL field in SQLBindCol?
> > > 
> > > Hi,
> > > 
> > > I am using FreeTDS as an ODBC driver talking to a SQLServer. This is
> under
> > > RedHat 7.3 with FreeTDS from about June 7 (one of the "current"
> versions).
> > > 
> > > My actual setup is to use Python and the mxODBC code talking to the
> > > unixODBC code. Everything works pretty well except there is a problem
> if
> > > the database entry is NULL (the column is typed as a float). When the
> DB
> > > has a NULL, the Python code gets back the previous value that was in
> that
> > > column; that is, it is referencing old, stale data.
> > > 
> > > The mxODBC code attempts to use SQLBindCol where possible. The problem
> > > appears to be that tds_convert() and its children (tds_convert_flt8()
> in
> > > this case) don't seem to check whether the NULL flag is set and thus
> clear
> > > the data field and length. mxODBC expects the length field to be set
> to
> > > SQL_NULL_DATA (which is -1 in sql.h).
> > > 
> > > So, where is the bug? I would be glad to help a little, but I am not
> very
> > > familiar with ODBC code. If someone can let me know what the right
> > > behaviour is, I can attempt a patch.
> > > 
> > > Thanks,
> > >           Paul Rensing
> > > 
> > > 
> 
> ---
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