Re: Clarification sought on deleting connection attributes

Tim Bunce wrote:
> On Mon, Jul 28, 2008 at 01:13:50PM +0100, Martin Evans wrote:
>> Hi,
>>
>> From the DBI::DBD docs in "The dbd_db_login6 method" I read:
>>
>> =====
>> Here’s how you fetch them; as an example we use hostname attribute,
>> which can be up to 12 characters long excluding null terminator:
>>
>> SV** svp;
>> STRLEN len;
>> char* hostname;
>>
>> if ( (svp = DBD_ATTRIB_GET_SVP(attr, "drv_hostname", 12)) && SvTRUE(*svp)) {
>>    hostname = SvPV(*svp, len);
>>    DBD__ATTRIB_DELETE(attr, "drv_hostname", 12); /* avoid later STORE */
>> } else {
>>     hostname = "localhost";
>> }
>> =====
>>
>> My question concerns the comment saying "avoid later STORE". If I have a 
>> DBD::ODBC specific attribute which a) may be specified on the connect call 
>> and b) is copied to any statement handles when they are created and c) may 
>> also be on a statement handle, should I be calling DBD__ATTRIB_DELETE? and 
>> what does that "avoid later STORE" really mean?
> 
> After $drh->connect(..., $attr) returns a handle DBI->connect(...)
> effectively does $dbh->STORE($_, $attr->{$_}) for keys %$attr;
> 
> If the handle has already dealt with the attribute during the drivers
> connect/login processing then the later STORE by the DBI is at best
> redundant and could, at worse, cause problems/errors/whatever.
> 
> So the driver can delete from %$attr any attributes it doesn't want the
> DBI to call STORE on later.
> 
> Tim.
> 
> p.s. patch to DBI::DBD docs most welcome!
> 
> 

Thanks for the clarification.

First patch appears to be:

DBD__ATTRIB_DELETE => DBD_ATTRIB_DELETE

as I can find the latter and not the former. Unless I've got something 
else wrong I get a segfault the minute I used DBD_ATTRIB_DELETE and I 
notice DBD::Oracle does not use it. Is anyone using DBD_ATTRIB_DELETE 
and can confirm it works? I am only doing:

/* odbc_putdata_start */
{
     SV **svp;
     IV putdata_start_value;

     DBD_ATTRIB_GET_IV(
         attr, "odbc_putdata_start", strlen("odbc_putdata_start"),
         svp, putdata_start_value);
     if (svp) {
         imp_dbh->odbc_putdata_start = putdata_start_value;
         if (DBIc_TRACE(imp_dbh, 0, 0, 3))
             TRACE1(imp_dbh, "    Setting DBH putdata_start to %d\n",
                    (int)putdata_start_value);
#ifdef THE_FOLLOWING_SEG_FAULTS
         /* avoid later STORE */
         DBD_ATTRIB_DELETE(attr, "odbc_putdata_start",
                           strlen("odbc_putdata_start"));
#endif
     }
}

Thanks

Martin
-- 
Martin J. Evans
Easysoft Limited
http://www.easysoft.com