Add columns to acq.purchase_order: order_date and name.

Add columns to acq.purchase_order: order_date and name.

Name defaults to the id, as text.

Name should be unique for a given ordering_agency and order
date (truncated to midnight), but only where order_date
is not null.

To change an existing table, run the following
through psql:

-- Add new columns; populate name

ALTER TABLE acq.purchase_order
ADD COLUMN order_date TIMESTAMP WITH TIME ZONE;

ALTER TABLE acq.purchase_order
ADD COLUMN name TEXT;

UPDATE acq.purchase_order
SET name = id::TEXT;

ALTER TABLE acq.purchase_order
ALTER COLUMN name SET NOT NULL;

-- Name should default to the id.  We can't do that with a DEFAULT
-- clause but we can do it with a trigger.

CREATE OR REPLACE FUNCTION acq.purchase_order_name_default () RETURNS TRIGGER
AS $$
BEGIN
	IF NEW.name IS NULL THEN
		NEW.name := NEW.id::TEXT;
	END IF;

	RETURN NEW;
END;
$$ LANGUAGE PLPGSQL;

CREATE TRIGGER po_name_default_trg
  BEFORE INSERT OR UPDATE ON acq.purchase_order
  FOR EACH ROW EXECUTE PROCEDURE acq.purchase_order_name_default ();

-- Name should be unique for a given ordering_agency and day, where
-- order_date is not null.  We can't do that with a check constraint
-- because it would require a subquery, so we use a trigger.

CREATE INDEX acq_po_org_name_order_date_idx
ON acq.purchase_order( ordering_agency, name, order_date );

CREATE OR REPLACE FUNCTION acq.po_org_name_date_unique () RETURNS TRIGGER
AS $$
DECLARE
	collision INT;
BEGIN
	--
	-- If order_date is not null, then make sure we don't have a collision
	-- on order_date (truncated to day), org, and name
	--
	IF NEW.order_date IS NULL THEN
		RETURN NEW;
	END IF;
	--
	-- In the WHERE clause, we compare the order_dates without regard to time of day.
	-- We use a pair of inequalities instead of comparing truncated dates so that the
	-- query can do an indexed range scan.
	--
	SELECT 1 INTO collision
	FROM acq.purchase_order
	WHERE
		ordering_agency = NEW.ordering_agency
		AND name = NEW.name
		AND order_date >= date_trunc( 'day', NEW.order_date )
		AND order_date <  date_trunc( 'day', NEW.order_date ) + '1 day'::INTERVAL
		AND id <> NEW.id;
	--
	IF collision IS NULL THEN
		-- okay, no collision
		RETURN NEW;
	ELSE
		-- collision; nip it in the bud
		RAISE EXCEPTION 'Colliding purchase orders: ordering_agency %, date %, name ''%''',
			NEW.ordering_agency, NEW.order_date, NEW.name;
	END IF;
END;
$$ LANGUAGE PLPGSQL;

CREATE TRIGGER po_org_name_date_unique_trg
  BEFORE INSERT OR UPDATE ON acq.purchase_order
  FOR EACH ROW EXECUTE PROCEDURE acq.po_org_name_date_unique ();

git-svn-id: svn://svn.open-ils.org/ILS/trunk@13924 dcc99617-32d9-48b4-a31d-7c20da2025e4