Re: [GENERAL] help with plpgsql function called by trigger

[Alban Hertroys]

Heather Johnson wrote:
Hello--
I need to make sure that every time a row is inserted into a table 
called "users" rows are automatically inserted into two other tables: 
"join_bd" and "behavior_demographics". The inserts on join_bd and 
behavior_demographics need to create rows that are keyed to the users 
table with an integer id (called "users_id"). The join_bd row that's 
created also needs to contain a key for a record in 
behavior_demographics (bd_id). Here's what I did to try and accomplish 
this:

CREATE FUNCTION insert_bd_join_bd (integer) RETURNS opaque AS '
declare
    r RECORD;
        uid ALIAS FOR $1;
begin
    INSERT INTO behavioral_demographics (users_id) VALUES (uid);
    SELECT INTO r bdid FROM behavioral_demographics WHERE users_id=uid;
    INSERT INTO join_bd (bd_id, users_id) VALUES (bdid, uid);
end;
' LANGUAGE 'plpgsql';
Wouldn't it be nicer to put the second part of that SP in a trigger on 
behavioral_demographics? That can only work if inserting into users is 
the only way to insert records into behavioral_demographics, of course.

I don't know the names of your columns in behavioral_demographics, but 
it would look something like this:

CREATE FUNCTION insert_bd () RETURNS trigger AS '
begin
    INSERT INTO behavioral_demographics (users_id)
    VALUES (NEW.users_id);      -- fires trigger on bd
end;
' LANGUAGE 'plpgsql';
CREATE FUNCTION insert_join_bd () RETURNS trigger AS '
begin
    INSERT INTO join_bd (bd_id, users_id)
    VALUES (NEW.bd_id, NEW.users_id);
end;
' LANGUAGE 'plpgsql';
CREATE TRIGGER insert_bd_on_users
AFTER INSERT ON users
FOR EACH ROW EXECUTE PROCEDURE insert_bd();
CREATE TRIGGER insert_join_bd_on_users
AFTER INSERT ON behavioral_demographics
FOR EACH ROW EXECUTE PROCEDURE insert_join_bd();
Considering these SP's are basically simple SQL statements, the triggers 
could also be implemented as a set of query rewrite rules (see CREATE 
RULE). That's usually more efficient, but I don't have a lot of 
experience with those...

Regards,
--
Alban Hertroys
MAG Productions
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