Re: using callbacks with connect_cached

[David E. Wheeler]

On Aug 24, 2013, at 9:40 PM, Vincent Veyron vv.li...@wanadoo.fr wrote:

 Not quite : I thought connected_cache.new would enable me to set the
 correct datestyle once for a cached connection, and then be cached with
 it, but we've seen that won't work.
 
 Using the connected callback would do a 'set datestyle to xyz' for each
 connection, even if cached. I realize it's no big deal (.5ms on my lowly
 Atom processor), but every little bit helps, as I'm sure you know. 
 
 So I now set the datestyle when the user logs in (hence once, with
 $dbh-do('SET datestyle TO xyz'), and the database handle is cached and
 reused as is.

You can also use a private attribute in connect_cached.new to tell the 
connected callback to do its thing:


my $cb = {
'connect_cached.new' = sub {
$_[4]-{private_is_new} = 1;
return;
},
connected = sub {
my $dbh = shift;
warn connected\n if delete $dbh-{private_is_new};
return;
}
};

for (1..3) {
DBI-connect_cached('dbi:SQLite:', '', '', {
PrintError = 0,
RaiseError = 1,
AutoCommit = 1,
Callbacks  = $cb,
});
}

This emits connected only once.

Best,

David

DBI - SQL Server - DAC Connection

[Roy Fulbright]

I am running Activestate Perl 5.8.9 on Windows 7. I have been able to establish 
a connection to MS SQL Server using DBI for years. What I need now is to 
establish a Dedicated Administrator Connection (DAC) to SQL Server via DBI. I 
can establish a DAC connection to SQL Server using sqlcmd in a cmd window by 
prepending ADMIN: to the server name or by using the -A option, and this 
works fine.  When I prepend ADMIN: to the server name in my DBI connection 
string I get the following error message: 
DBI connect('Driver={SQL 
Server};Server=ADMIN:localhost\SQLEXPRESS;Database=pubs','sa',...) failed: 
MicrosoftODBC SQL Server DriverDBNETLIBSQL Server does not exist or access 
denied. (SQL-08001) state was 08001 now 01000  When I add the DAC listening 
port to the end of the server name in my DBI connection string I get the 
following error message: 
DBI connect('Driver={SQL 
Server};Server=localhost\SQLEXPRESS,60488;Database=pubs','sa',...) failed: 
MicrosoftODBC SQL Server DriverDBNETLIBInvalid connection. (SQL-08001) state 
was 08001 now 01000  
I have tried Super Search and Google, and have come up empty.
 
Does anyone know how to establish a DAC connection to SQL Server using DBI? 

Thanks,
Roy Fulbright
 
Also posted on Perlmonks at: http://perlmonks.org/?node_id=1050822
 
  

Re: using callbacks with connect_cached

[Tim Bunce]

On Sun, Aug 25, 2013 at 01:38:57PM +0200, David E. Wheeler wrote:
 On Aug 24, 2013, at 9:40 PM, Vincent Veyron vv.li...@wanadoo.fr wrote:
 
 You can also use a private attribute in connect_cached.new to tell the 
 connected callback to do its thing:
 
 my $cb = {
 'connect_cached.new' = sub {
 $_[4]-{private_is_new} = 1;
 return;
 },
 connected = sub {
 my $dbh = shift;
 warn connected\n if delete $dbh-{private_is_new};
 return;
 }
 };
 
 for (1..3) {
 DBI-connect_cached('dbi:SQLite:', '', '', {
 PrintError = 0,
 RaiseError = 1,
 AutoCommit = 1,
 Callbacks  = $cb,
 });
 }
 
 This emits connected only once.

If you're going to use a callback on connected and an attribute then
there's no need to also use connect_cached.new. Just this should do:

  connected = sub {
  my $dbh = shift;
  if (++$dbh-{private_connected_count} == 1) {
  ... # is new connection
  }
  return;
  }

Tim.

p.s. I'd be delighted to get a doc patch that notes the need to use a
lexical for the callbacks hashref on connect_cached.

p.p.s. I'd also consider a patch to add a 'connect_cached.connected'
callback for new connections.

Re:

[David E. Wheeler]

On Aug 26, 2013, at 2:42 AM, Vincent Veyron vv.li...@wanadoo.fr wrote:

 Right now, I'm left wondering *how* I am going to pass said lexical to
 the package 'db_handle' I pasted in the message that started the thread,
 in the context of mod_perl, so not sure about writing up on it yet.

Even though you’re using connect_cached(), you should consider holding on to 
the DBI handle yourself somewhere. Like in an attribute of a singleton object. 
You might find DBIx::Connector useful to use that way, rather than 
connect_cached().

Best,

David