Aaron Bono wrote:
On 7/19/06, *Collin Peters* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
I am learning about how to use rules to handle a multi-table insert.
Right now I have a user_activity table which tracks history and a
user_activity_users table which tracks what users are associated with
a row in user_activity (one to many relationship).
I created a rule (and a view called user_activity_single) which is to
simplify the case of inserting a row in user_activity in which there
is only one user in user_activity_users.
CREATE OR REPLACE RULE user_activity_single_insert AS
ON INSERT TO user_activity_single
DO INSTEAD (
INSERT INTO user_activity(
user_activity_id,
description,
...
)
VALUES (
NEW.user_activity_id,
NEW.description,
...
);
INSERT INTO user_activity_users (
user_activity_id,
user_id
)
VALUES (
NEW.user_activity_id,
NEW.user_id
);
);
This works well by itself, but the problem is that I have to manually
pass in the user_activity_id which is the primary key. I do this by
calling nextval to get the next ID in the sequence.
Is there any way to have the rule handle the primary key so I don't
have to pass it in? It seems you can't use pgsql inside the rule at
all. What I'm looking for is something like:
CREATE OR REPLACE RULE user_activity_single_insert AS
ON INSERT TO user_activity_single
DO INSTEAD (
SELECT nextval('user_activity_user_activity_id_seq') INTO
next_id;
INSERT INTO user_activity(
user_activity_id,
description,
...
)
VALUES (
next_id,
NEW.description,
...
);
INSERT INTO user_activity_users (
user_activity_id,
user_id
)
VALUES (
next_id,
NEW.user_id
);
);
Note the sequence stored in next_id. This doesn't work as it
complains about next_id in the INSERT statements. Any way to do
something like this? I suppose I could create a function and then
have the rule call the function but this seems like overkill.
Since I have not tried something like this before, I may be off base
but have you tried:
CREATE OR REPLACE RULE user_activity_single_insert AS
ON INSERT TO user_activity_single
DO INSTEAD (
INSERT INTO user_activity(
description,
...
)
VALUES (
NEW.description,
...
);
INSERT INTO user_activity_users (
user_activity_id,
user_id
)
VALUES (
SELECT currval('user_activity_user_activity_id_seq'),
NEW.user_id
);
);
I am assuming user_activity.user_activity_id is a BIGSERIAL or SERIAL.
By coincidence, I had to work this out just the other day for a project
that I'm working on. Aaron's solution looks correct, although you can
just call currval() without the SELECT in this context.
What Collin may not be aware of is that currval(seqX) returns the last
value generated by nextval(seqX) in the same session, so there is no
race between your session and other sessions that may be using the same
sequence. So it's safe to let the insert trigger the next value
automatically, and then call currval(). In contrast, don't use lastval()
for this.
Ross Johnson
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