Date: Mon, 10 Dec 2007 12:29:15 +0100
From: "A. Kretschmer" <andreas.kretschmer@schollglas.com>
To: pgsql-sql@postgresql.org
Subject: Re: INSERT INTO relational tables
Message-ID: <20071210112915.GF917@a-kretschmer.de>
References: <20071207172528.820B92C96D4@maia-2.hub.org>
	<20071209075032.2A1112E3294@postgresql.org>
	<20071210104204.324340@gmx.net>
	<20071210110848.GE917@a-kretschmer.de>
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am  Mon, dem 10.12.2007, um 12:08:48 +0100 mailte A. Kretschmer folgendes:
> am  Mon, dem 10.12.2007, um 11:42:04 +0100 mailte Stefan Scheidegger folgendes:
> > Thanks for your hints so far.
> > 
> > I'm looking for both syntax simplicity and referential integrity. I'm
> > using c++ with libpqxx, but I didn't find a good object-relational
> > mapper. And I'm too lazy to implement a whole persistency layer as I
> > don't have a huge DB with many relations.
> > 
> > I tried Andreas' suggestion with a RULE for INSERT on a VIEW. I
> > created the VIEW composing my table with customers and orders:
> > 
> > CREATE VIEW vw_customer_insert AS SELECT * FROM tbl_customer,
> > tbl_order WHERE cust_id = ord_customer;
> > 
> > Then I added a rule for the inserting: CREATE RULE rl_customer_insert
> > AS ON INSERT TO vw_customer_insert DO INSTEAD ( INSERT INTO
> > tbl_customer VALUES (DEFAULT, new.cust_name, new.cust_address); INSERT
> > INTO tbl_order VALUES (NEW.ord_pieces, NEW.ord_productname,
> > NEW.ord_price, currval('"tbl_cusomer_cust_id_seq"')););
> > 
> > But this results in the same problem: It works fine if I insert just
> > one new customer with one new order. But if I want to insert several
> > new entries:
> 
> Insert the new customer only into the table if this customer doesn't
> exist there. If the customer exist in the table, obtain the id for this
> customer.
> 
> 
> 
> simplified:
> 
> - detect, if the customer exists
>   yes: obtain the id as id
>   no: insert and use currval() as id
> - insert the order with the id
> 
> 
> I would write a function for this.

a little example:

test=# create table customer (id serial primary key, name text);
NOTICE:  CREATE TABLE will create implicit sequence "customer_id_seq" for serial column "customer.id"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "customer_pkey" for table "customer"
CREATE TABLE
test=*# create table orders (customer int references customer, val int);
CREATE TABLE
test=*# create or replace function orders_insert (text, int) returns int
as $$declare i int;begin select into i id from customer where name=$1;
if i is null then insert into customer (name) values ($1); select into i
currval('customer_id_seq'); end if; insert into orders values (i,$2);
return i; end; $$language plpgsql;
CREATE FUNCTION
test=*# select * from customer;
 id | name
----+------
(0 rows)

test=*# select * from orders ;
 customer | val
----------+-----
(0 rows)

test=*# select orders_insert('foo',1);
 orders_insert
---------------
             1
(1 row)

test=*# select orders_insert('foo',2);
 orders_insert
---------------
             1
(1 row)

test=*# select orders_insert('foo',3);
 orders_insert
---------------
             1
(1 row)

test=*# select orders_insert('bar',4);
 orders_insert
---------------
             2
(1 row)

test=*# select * from customer;
 id | name
----+------
  1 | foo
  2 | bar
(2 rows)

test=*# select * from orders ;
 customer | val
----------+-----
        1 |   1
        1 |   2
        1 |   3
        2 |   4
(4 rows)


HTH, Andreas
-- 
Andreas Kretschmer
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