From 9c1bed218903d43b9a78a67e1a43671f8125d911 Mon Sep 17 00:00:00 2001
From: Michael Hierweck <michael@hierweck.de>
Date: Fri, 26 Apr 2019 10:04:06 +0200
Subject: [PATCH] Historicization with PostgreSQL improved.

---
 sql/history-demo.sql | 45 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 37 insertions(+), 8 deletions(-)

diff --git a/sql/history-demo.sql b/sql/history-demo.sql
index 0d7ec31f..df21171d 100644
--- a/sql/history-demo.sql
+++ b/sql/history-demo.sql
@@ -1,16 +1,16 @@
 CREATE FUNCTION historicize() RETURNS trigger
-    LANGUAGE plpgsql SECURITY DEFINER
-    AS $$
+AS $$
 BEGIN
     IF (TG_OP = 'INSERT') OR (TG_OP = 'UPDATE') THEN
-        EXECUTE format('INSERT INTO ' || TG_TABLE_NAME || '_history VALUES (DEFAULT, now(), txid_current(), False, $1.*)') USING NEW;
+        EXECUTE format('INSERT INTO %I_history VALUES (DEFAULT, now(), txid_current(), False, $1.*)', TG_TABLE_NAME) USING NEW;
         RETURN NEW;
     ELSE
-        EXECUTE format('INSERT INTO ' || TG_TABLE_NAME || '_history VALUES (DEFAULT, now(), txid_current(), True, $1.*)') USING OLD;
+        EXECUTE format('INSERT INTO %I_history VALUES (DEFAULT, now(), txid_current(), True, $1.*)', TG_TABLE_NAME) USING OLD;
         RETURN OLD;
     END IF;
 END;
-$$;
+$$
+LANGUAGE plpgsql;
 
 CREATE TABLE person (
     id serial PRIMARY KEY,
@@ -30,6 +30,38 @@ CREATE TABLE person_history (
 
 CREATE TRIGGER person_historicize AFTER INSERT OR DELETE OR UPDATE ON person FOR EACH ROW EXECUTE PROCEDURE historicize();
 
+CREATE OR REPLACE FUNCTION person_history(transaction bigint, VARIADIC groupby text[]) RETURNS TABLE (
+    history_id integer,
+    history_timestamp timestamp,
+    history_transaction bigint,
+    history_tombstone boolean,
+    id integer,
+    name character varying(50),
+    email character varying(50)
+)
+AS $$
+BEGIN
+    RETURN QUERY EXECUTE format('SELECT * FROM person_history WHERE history_id IN (SELECT max(history_id) AS history_id FROM person_history WHERE history_transaction <= $1 GROUP BY %s)', array_to_string(groupby, ', ')) USING transaction;
+END;
+$$
+LANGUAGE plpgsql;
+
+CREATE OR REPLACE FUNCTION person_history(VARIADIC groupby text[]) RETURNS TABLE (
+    history_id integer,
+    history_timestamp timestamp,
+    history_transaction bigint,
+    history_tombstone boolean,
+    id integer,
+    name character varying(50),
+    email character varying(50)
+)
+AS $$
+BEGIN
+    RETURN QUERY EXECUTE format('SELECT * FROM person_history WHERE history_id IN (SELECT max(history_id) AS history_id FROM person_history GROUP BY %s)', array_to_string(groupby, ', '));
+END;
+$$
+LANGUAGE plpgsql;
+
 INSERT INTO person (name, email) VALUES ('michael', 'michael@hierweck.de');
 INSERT INTO person (name, email) VALUES ('annika', 'annika@hierweck.de');
 
@@ -48,6 +80,3 @@ INSERT INTO person (name, email) VALUES ('ax', 'ax@hierweck.de');
 UPDATE person SET email='mxx@hierweck.de' WHERE name='mx';
 UPDATE person SET email='axx@hierweck.de' WHERE name='ax';
 COMMIT;
-
-SELECT * FROM person_history WHERE history_id IN (SELECT max(history_id) AS history_id FROM person_history WHERE history_transaction <= 12345 GROUP BY id);
-SELECT * FROM person_history WHERE history_id IN (SELECT max(history_id) AS history_id FROM person_history WHERE history_transaction <= 12345 GROUP BY name);