... because one can build amazing database APIs with it by using views to their full extent:
BEGIN;
CREATE TABLE moo (
id uuid NOT NULL PRIMARY KEY,
relation regclass NOT NULL
);
CREATE FUNCTION moo(regclass, uuid) RETURNS uuid LANGUAGE sql AS $$
INSERT INTO moo (id, relation) VALUES ($2, $1) RETURNING id;
$$;
CREATE TABLE foo (
id uuid NOT NULL DEFAULT uuid_generate_v1() PRIMARY KEY REFERENCES moo,
name text NOT NULL UNIQUE
);
CREATE VIEW foos AS SELECT id, name FROM foo;
ALTER VIEW foos ALTER COLUMN id SET DEFAULT uuid_generate_v1();
CREATE RULE "_INSERT" AS ON INSERT TO foos DO INSTEAD
INSERT INTO foo (id, name) SELECT moo('foo'::regclass, NEW.id), NEW.name RETURNING *;
INSERT INTO foos (id, name) VALUES ('17ee2d5a-4164-11df-be2f-0019dbf67458', 'a') RETURNING *;
INSERT INTO foos (id, name) VALUES ('1cf57cb8-4164-11df-9159-0019dbf67458', 'b') RETURNING *;
INSERT INTO foos (name) VALUES ('c') RETURNING *;
COMMIT;
... results in:
BEGIN
psql:rules-and-rocks.sql:7: NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "moo_pkey" for table "moo"
CREATE TABLE
CREATE FUNCTION
psql:rules-and-rocks.sql:16: NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "foo_pkey" for table "foo"
psql:rules-and-rocks.sql:16: NOTICE: CREATE TABLE / UNIQUE will create implicit index "foo_name_key" for table "foo"
CREATE TABLE
CREATE VIEW
ALTER VIEW
CREATE RULE
id | name
--------------------------------------+------
17ee2d5a-4164-11df-be2f-0019dbf67458 | a
(1 row)
INSERT 0 1
id | name
--------------------------------------+------
1cf57cb8-4164-11df-9159-0019dbf67458 | b
(1 row)
INSERT 0 1
id | name
--------------------------------------+------
e087171c-4174-11df-856c-0019dbf67458 | c
(1 row)
INSERT 0 1
COMMIT
But take care with rules... is what i've been told nearly agressively... because they're dangerous and come with pitfalls.
More gently said: RTFM! Twice! ;-)
