[asterisk-dev] tilghman: trunk r247787 - /trunk/channels/chan_sip.c

[Tony Mountifield]

In article <E1NiE9D-0006zA-5x at wibble.digium.internal>,
SVN commits to the Digium repositories <svn-commits at lists.digium.com> wrote:
> Author: tilghman
> Date: Thu Feb 18 15:42:53 2010
> New Revision: 247787
> 
> URL: http://svnview.digium.com/svn/asterisk?view=rev&rev=247787
> Log:
> If the peer record is from realtime, it could be set to 0, due to MySQL not representing
> NULL well in integer columns.
> 
> NULL means the value is not specified for the column, which normally means
> the driver uses whatever is the default value.  However, on MySQL, placing
> a NULL in either a float or integer column results in a retrieval of the 0
> value.  Hence, users get an errant error on load.  This patch suppresses
> that error and makes the value as if it was not there.
> 
> Note that this cannot be done in the realtime driver, because the lack of
> difference between NULL and 0 can only be intepreted correctly by the
> driver itself.  If we did it in the realtime driver, then it would be
> effectively impossible to set any realtime field to 0, because it would act
> as if the field were unspecified and possibly take on a different value.

Whether or not the patch is useful, I don't know, but the above description
of MySQL behaviour is surely wrong.

MySQL is can easily distinguish between 0 and NULL in numeric columns.

If you have the statement: row = mysql_fetch_row(result);
then row[n]==NULL if the corresponding column contains an SQL NULL, but if
the column contains a zero, row[n] points to the string "0".

The information is not getting lost in MySQL, but probably in
res_config_mysql.c in one or more of the functions realtime_mysql(),
realtime_multi_mysql() and config_mysql(), where a NULL is being converted to
an empty string. Such a string will indeed yield a numeric 0 if you give it
to something like strtoul().

Cheers
Tony

-- 
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org