A long time ago, in a galaxy far, far away, florence.henry@obspm.fr (Florence HENRY) wrote:
> well, almost everything is in the subject !
>
> I have to fill 2 tables (more complicated than in the example !):
>
> CREATE TABLE A (
> id serial primary key,
> foo text);
>
> CREATE TABLE B (
> id serial references A,
> bar text);
>
> I fill A with :
> INSERT into A VALUES (DEFAULT, "toto");
>
> Then I need to retreive the "A.id" that was given to A, in order to give it
> to B.id. If I was doing this by hand, it would have been quite easy, but I'm
> doing this with a script.
>
> So, if I make a SELECT id from A; and take the last row, will it *always*
> be the row that I've just inserted.
This won't happen "implicitly."
tutorial=# CREATE TABLE A (id serial primary key,foo text);
NOTICE: CREATE TABLE will create implicit sequence "a_id_seq" for "serial" column "a.id"
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "a_pkey" for table "a"
CREATE TABLE
tutorial=# drop table b;
DROP TABLE
tutorial=# CREATE TABLE B (id serial references A,bar text);
NOTICE: CREATE TABLE will create implicit sequence "b_id_seq" for "serial" column "b.id"
CREATE TABLE
I can suggest a couple of ways you might do this:
1. So long as the inserts take place within the scope of the same
transaction on the same connection, it would be safe to create
the B entry via currval for the sequence.
tutorial=# begin;
BEGIN
tutorial=# insert into a (foo) values ('toto');
INSERT 2587831 1
tutorial=# insert into b (id, bar) values (currval('a_id_seq'), 'yellow brick road');
INSERT 2587832 1
tutorial=# commit;
COMMIT
Note that if you don't enclose it in BEGIN/COMMIT, the insert into b
could pick up on changes from other concurrent sessions.
2. You might create a stored procedure that creates both entries,
using currval() behind your back.
[assuming suitably-created funciton...
select make_foo_bar ('toto', 'yellow brick road');
This won't work so well if there are to be multiple associations; if
that be the case, you'd want to have an explicit external primary key,
and do something like:
select create_a ('toto', 'key-for-toto');
select link_b_to_a ('key-for-toto', 'yellow brick road');
select link_b_to_a ('key-for-toto', 'click, click');
select link_b_to_a ('key-for-toto', 'ruby shoes');
There's no magic there; the stored procedure link_b_to_a() would look
up the ID number for 'key-for-toto' in table A.
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