Re: Firing trigger if only

On Thu, Apr 3, 2014 at 8:50 AM, Gabriel <yu1nis(at)gmail(dot)com> wrote:

> Good afternoon all.I have some problem with triggers on PostgreSQL 8.4.I
> have
> a trigger on specific table(articles) that fires on update statement:
>
> CREATE OR REPLACE FUNCTION trigger_articles_update()
> RETURNS trigger AS
> $BODY$BEGIN
> INSERT INTO
> article_change(article_id,change_type)VALUES(OLD.article_id,2);
> RETURN NULL;
> END$BODY$
> LANGUAGE 'plpgsql' VOLATILE
> COST 100;
> ALTER FUNCTION trigger_articles_update() OWNER TO postgres;
>
> I have 2 different applications that performs update on table
> articles(written in Delphi and using ZeosDB). My problem is that I want
> trigger to fire only when performing update with first application, but not
> with second.I know that triggers supposed to fire on every change on table,
> but this is a specific problem that I have.Any hint appreciated. 8)
>
>
Since 9.0 version of PostgreSQL you can set 'application_name' in
connection [1] and test it in your trigger using a query like:

regress=# SELECT application_name FROM pg_stat_activity WHERE pid =
pg_backend_pid();
application_name
------------------
psql
(1 registro)

I strongly recommend you to upgrade your 8.4 because the EOL [2] is July
2014.

But if an upgrade isn't an option for now then you can use the old
"custom_variable_classes" to set your application, i.e.:

1) Add to your postgresql.conf:

custom_variable_classes = 'foo'
foo.application_name = 'undefined'

2) Reload your PostgreSQL

3) You can use the following functions to get/set the
'foo.application_name' custom variable:

-- get
SELECT current_setting('foo.application_name');

-- set
SELECT set_config('foo.application_name', 'myapp');

4) Now you can use this functions do register the name of your application
an use it in your trigger.

Regards,

[1]
http://www.postgresql.org/docs/current/static/runtime-config-logging.html#GUC-APPLICATION-NAME
[2] http://www.postgresql.org/support/versioning/
[3] http://www.postgresql.org/docs/8.4/static/runtime-config-custom.html
--
Fabrízio de Royes Mello
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