Обсуждение: Multi-row update w. plpgsql

Given a set of checkbox values that are submitted through an html form,
how do you loop through the submitted values to update more than one row
in a table?

Imagine a table called 'message_table':

mid | message | status
----+---------+-------
  1  |  Text1   |  H
  2  |  Text2   |  H
  3  |  Text3   |  H
  4  |  Text4   |  H

A web page presents the user with all messages flagged with 'H'. User
checks messages 1,3 and 4 and submits form.
(i.e. approved=1&approved=3&approved=4)

After performing postgreSQL update, rows 1, 3 and 4 would be updated to:

mid | message | status
----+---------+-------
  1  |  Text1   |  A
  2  |  Text2   |  H
  3  |  Text3   |  A
  4  |  Text4   |  A

I have never written a plpgsql function, but tried:

CREATE OR REPLACE FUNCTION update_messages(approved integer) RETURNS
integer AS
$body$
DECLARE
 new_status varchar;
 new_sample record;

BEGIN
 new_status := 'A';

 FOR new_sample IN SELECT * FROM message_table WHERE status='H' ORDER BY
mid LOOP
  UPDATE message_table SET status = new_status
  WHERE mid = approved;
 END LOOP;

 RETURN 1;
END;
$body$
LANGUAGE 'plpgsql' VOLATILE CALLED ON NULL INPUT SECURITY INVOKER;

I call the function with:
SELECT update_messages(<xsp-request:get-parameter name="accepted"/>);

I'm using apache cocoon, which is why you see the variable placeholder:
<xsp-request:get-parameter name="accepted"/>);

Unfortunately, the function only updates the first value submitted (mid
1), and doesn't loop through the other two values submitted.

Can someone help this novice from getting ulcers?

Thanks for your help!

Daniel

On Tue, 2005-12-13 at 15:57 -0700, Daniel Hertz wrote:
> Given a set of checkbox values that are submitted through an html form,
> how do you loop through the submitted values to update more than one row
> in a table?
...
>
> I have never written a plpgsql function, but tried:
>
> CREATE OR REPLACE FUNCTION update_messages(approved integer) RETURNS
> integer AS
> $body$
> DECLARE
>  new_status varchar;
>  new_sample record;
>
> BEGIN
>  new_status := 'A';
>
>  FOR new_sample IN SELECT * FROM message_table WHERE status='H' ORDER BY
> mid LOOP
>   UPDATE message_table SET status = new_status
>   WHERE mid = approved;
>  END LOOP;

I can't see what you are looping for; you don't use new_sample inside
the loop so the loop is completely redundant.  I think this will just
update the same row in the same way as many times as there are
new_sample rows.

>  RETURN 1;
> END;
> $body$
> LANGUAGE 'plpgsql' VOLATILE CALLED ON NULL INPUT SECURITY INVOKER;
>
> I call the function with:
> SELECT update_messages(<xsp-request:get-parameter name="accepted"/>);
>
> I'm using apache cocoon, which is why you see the variable placeholder:
> <xsp-request:get-parameter name="accepted"/>);

Since this is updating something, I assume that is putting in a single
value of "approved".  Perhaps you need to do the loop in the application
program.
>
> Unfortunately, the function only updates the first value submitted (mid
> 1), and doesn't loop through the other two values submitted.

I suggest you put in some RAISE NOTICE statements so you can see what is
actually happening.

--
Oliver Elphick                                          olly@lfix.co.uk
Isle of Wight                              http://www.lfix.co.uk/oliver
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