Re: INSERT INTO relational tables

From: "Stefan Scheidegger" <Stefan(dot)Scheidegger(at)gmx(dot)net>
To: pgsql-sql(at)postgresql(dot)org
Subject: Re: INSERT INTO relational tables
Date: 2007-12-10 10:42:04
Message-ID: 20071210104204.324340@gmx.net
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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 INTO vw_customer_insert(cust_name, cust_address, ord_pieces, ord_productname, ord_price)
VALUES ), (‘MR. X’, ‘1st street’, 5, ‘books’, 50), (‘MRS. Y’, ‘2nd street’, 1, ‘t-shirt’, 10);

This doesn't work correctly; all orders are now related to the last customer. In this example, both orders are related to MRS. Y because I use currval() in my insert rule.

Do you see any solution for this? I thought that the performance of this would be better than INSERTing to tbl_customer, fetching the ID and then do several INSERTS to tbl_order in c++. But actually I tend to do it with several INSERT statements in one transaction, as Steve proposed.

Cheers Stefan

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