Rule or Function and Trigger?

"James B. Byrne" <byrnejb@harte-lyne.ca> writes:

I am beginning to migrate some functionality from an application
prototype into the DBMS. One of these elements is time stamping row
insertions and updates.

I have been reading about rules, functions and triggers in regards
to this issue. So, of course, now I have myself completely
befuddled. From what I can determine from the documentation, it
makes little difference to the DBMS whether I set a rule on insert
and one on update for each table or define a function and set a
trigger for insert or update on each table.

If this is indeed the case then which way is the preferred method?

A trigger is very much preferred. Rules are not as easy as they look.
Triggers are a bit more notationally cumbersome, but they tend to
do what you expect without any surprises.

For the problem you mention, a stripped-down version of the first
example here is what you want:
http://www.postgresql.org/docs/8.3/static/plpgsql-trigger.html

regards, tom lane

Il giorno 03/apr/09, alle ore 16:58, Tom Lane ha scritto:

"James B. Byrne" <byrnejb@harte-lyne.ca> writes:

I am beginning to migrate some functionality from an application
prototype into the DBMS. One of these elements is time stamping row
insertions and updates.

I have been reading about rules, functions and triggers in regards
to this issue. So, of course, now I have myself completely
befuddled. From what I can determine from the documentation, it
makes little difference to the DBMS whether I set a rule on insert
and one on update for each table or define a function and set a
trigger for insert or update on each table.

If this is indeed the case then which way is the preferred method?

A trigger is very much preferred. Rules are not as easy as they look.
Triggers are a bit more notationally cumbersome, but they tend to
do what you expect without any surprises.

Are there some situations when using a rule is clearly superior than a
trigger?

I experimented with rules, with good result, but I’d rethink my
approach if triggers are more "reliable".

Thank you in advance

--
Giorgio Valoti