Listen and Notify

On Mon, Apr 30, 2012 at 1:47 AM, Alexander Reichstadt <lxr@mac.com> wrote:

Hi,

From the documentation I was able to build a trigger firing upon deletion of a record a function that delivers tablename_operation as a notification one needs to subscribe to. So in terminal I can say LISTEN persons_delete and instantly will receive

       Asynchronous notification "persons_delete" received from server process with PID 54790.

if there was a delete. But what I don't fully understand is how to do this with PQnotifies. Following the docu I get no notifications even though I subscribe to them after successfully connecting to the server the same way I do using terminal.

Googling didn't give me examples I was able to use. Please, can someone help?

I'm suspecting operator error because using PQnotifies is exactly what
psql does. Maybe you could post a small test program? Are you using
a mixed case notification name?

merlin

Alexander Reichstadt <lxr@mac.com> writes:

But what I don't fully understand is how to do this with PQnotifies. Following the docu I get no notifications even though I subscribe to them after successfully connecting to the server the same way I do using terminal.

Maybe you forgot PQconsumeInput? There's a working example in the
source tree:

http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/test/examples/testlibpq2.c

regards, tom lane

Merlin Moncure wrote:

On Mon, Apr 30, 2012 at 1:47 AM, Alexander Reichstadt <lxr@mac.com> wrote:

Hi,

From the documentation I was able to build a trigger firing upon deletion of a record a function that delivers tablename_operation as a notification one needs to subscribe to. So in terminal I can say LISTEN persons_delete and instantly will receive

Asynchronous notification "persons_delete" received from server process with PID 54790.

if there was a delete. But what I don't fully understand is how to do this with PQnotifies. Following the docu I get no notifications even though I subscribe to them after successfully connecting to the server the same way I do using terminal.

Googling didn't give me examples I was able to use. Please, can someone help?

I'm suspecting operator error because using PQnotifies is exactly what
psql does. Maybe you could post a small test program? Are you using
a mixed case notification name?

Works here in a Pascal program built using Lazarus. You /must/ however,
ensure that the session requesting the notification is kept active and
is the one that's regularly checked, it's easy to lose track of this in
a development framework which isolates you from the low-level handles etc.

--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]

The framework I am using is PGSQLKit for Mac OS X for which the source was available and which I downloaded and altered since. Actually it gives you access down to the pqlib calls.

The connection being closed was one of the issues. I had added convenience classes with class methods to the framework. The connection was kept in the background with its credentials and settings in place, but only opened on a per-request basis and closed afterwards which I changed now and now it works.

As to mixed case, no, it was all lower case, but using terminal for verification I had taken this into consideration so for listener and notifier to match.

Am 01.05.2012 um 14:51 schrieb Mark Morgan Lloyd: