Thread: Listen and Notify
Hi,
From the documentation I was able to build a trigger firing upon deletion of a record a function that delivers
tablename_operationas a notification one needs to subscribe to. So in terminal I can say LISTEN persons_delete and
instantlywill 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
notificationseven 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?
Thanks
Alex
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 thoughI 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
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_operationas a notification one needs to subscribe to. So in terminal I can say LISTEN persons_delete and instantlywill 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 nonotifications 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
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_operationas a notification one needs to subscribe to. So in terminal I can say LISTEN persons_delete and instantlywill 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 nonotifications 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. Theconnection was kept in the background with its credentials and settings in place, but only opened on a per-request basisand 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 forlistener and notifier to match. Am 01.05.2012 um 14:51 schrieb Mark Morgan Lloyd: > 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_operationas a notification one needs to subscribe to. So in terminal I can say LISTEN persons_delete and instantlywill 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 getno 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 notificationis kept active and is the one that's regularly checked, it's easy to lose track of this in a development frameworkwhich 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] > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general