ON INSERT view rule

[Anthony Chavez <acc@xxxxxxxxxxxxxxxxx>]

Hello, pgsql-general!

I originally posted this to pgsql-sql, but after not seing any
response for roughly a day and after re-reading the charters, I felt
that pgsql-general might be more appropriate.

What I've got here are a couple of ON INSERT rules for a view.  The
second rule is what I'm concerned about.  I wrote it with PostgreSQL's
ACID compliance in mind, but can I trust it?

From what I gather, if I were to simply use NEW.address_line_id rather
than address_lines_id_seq.last_value, it would be replaced by
nextval(address_line_id_seq), so I'm trying to work around that.

If there is there a better way to do this, I'm all ears.  Would
lastval() work for me in this case?  Thanks!

There is probably a better way of accomplishing what I'm after, but
this is the design that we've come up with, and the one that we're
more-or-less stuck with for the time being.  There are 2 additional
things that we implemented that aren't shown in the code below.

1. The addresses_address_lines view assumes that a row already exists
   in the addresses relation because that relation has some NOT NULL
   attributes that lack defaults.  Hence, there is no insert_addresses
   rule.  I suppose I should create one, but choosing a default value
   for some of the foreign keys in that relation (which are allowed to
   be NULL) would be difficult.

2. I have an AFTER INSERT trigger function on the addresses relation
   that inserts a default display_orderings tuple (with ordering = 0)
   and sets up the association in the junctions table.  Hence the use
   of UPDATE in the insert_display_orderings rule.

-- 
Anthony Chavez                                 http://anthonychavez.org/
mailto:acc@xxxxxxxxxxxxxxxxx         jabber:acc@xxxxxxxxxxxxxxxxxxxxxxxx

CREATE OR REPLACE VIEW addresses_address_lines
AS
SELECT a.id AS address_id,
       al.id AS address_line_id,
       line,
       ordering
  FROM addresses a
       INNER JOIN
       address_lines al
       ON al.address_id = a.id
       LEFT OUTER JOIN
       junctions
       ON parent_table = 'address_lines'
          AND parent_id = al.id
          AND child_table = 'display_orderings'
       LEFT OUTER JOIN
       display_orderings o
       ON o.id = child_id;

CREATE OR REPLACE RULE insert_address_lines
AS ON INSERT
TO addresses_address_lines
DO INSTEAD
INSERT INTO address_lines (address_id, line)
VALUES (NEW.address_id, NEW.line);

CREATE OR REPLACE RULE insert_display_orderings
AS ON INSERT
TO addresses_address_lines
DO
UPDATE display_orderings
   SET ordering = NEW.ordering
  FROM address_lines_id_seq
       INNER JOIN
       junctions
       ON parent_table = 'address_lines'
          AND parent_id = last_value
          AND child_table = 'display_orderings'
 WHERE ordering <> NEW.ordering
       AND display_orderings.id = child_id;

-- 
Anthony Chavez                                 http://anthonychavez.org/
mailto:acc@xxxxxxxxxxxxxxxxx         jabber:acc@xxxxxxxxxxxxxxxxxxxxxxxx

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