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On Tuesday 17 June 2003 05:13, Anagha Joshi wrote:
> Hi All,
> I'm new to Postgres. I'm using Postgres-7.2.4
> Can anybody guide me in detail how 'NOTIFY-LISTEN' can be implemented
> progmatically bet'n frontend and backend?
>
Might want to move this to the SQL list.
The idea is that a process will LISTEN for some notification. Another process
will NOTIFY that notification, and the one listening will get a message.
This is useful for a couple of things.
If you have an app that shows something like customer data, then you might
want to update the customer info when it changes.
Here's the table:
CREATE TABLE customer ( customer_id SERIAL PRIMARY KEY , first_name VARCHAR(20) NOT NULL , last_name
VARCHAR(20)NOT NULL);
When displaying the customer info for customer_id 19291, you could do
something like:
LISTEN customer_19291;
Now when someone else goes in and changes the customer info in the database,
you can have a trigger set up that will NOTIFY.
CREATE OR REPLACE FUNCTION notify_on_update() RETURNS TRIGGER AS ' BEGIN EXECUTE ''NOTIFY
''||TG_RELNAME||''_''||NEW.customer_id; RETURN NEW;END' LANGUAGE 'plpgsql';
CREATE TRIGGER notify_on_update AFTER update ON customerFOR EACH ROW EXECUTE PROCEDURE notify_on_update();
Now you set up your application to watch for the notification. When it
receives the notification, if can update the displayed information.
Is this a good starting place?
- --
Jonathan Gardner <jgardner@jonathangardner.net>
(was jgardn@alumni.washington.edu)
Live Free, Use Linux!
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