From 1e0d34306c3ecffe65abd30d2e82cf671c055345 Mon Sep 17 00:00:00 2001
From: Michael Hierweck <michael@hierweck.de>
Date: Sat, 4 May 2019 10:24:29 +0200
Subject: [PATCH] Transaction as foreign key. Example usage.

---
 sql/history-demo.sql | 93 +++++++++++++++++++++++++++-----------------
 1 file changed, 58 insertions(+), 35 deletions(-)

diff --git a/sql/history-demo.sql b/sql/history-demo.sql
index df21171d..df6493a7 100644
--- a/sql/history-demo.sql
+++ b/sql/history-demo.sql
@@ -1,17 +1,33 @@
+--
+-- Historization
+--
+
+CREATE TABLE history (
+    history_id serial PRIMARY KEY,
+    history_transaction bigint NOT NULL UNIQUE,
+    history_timestamp timestamp NOT NULL
+);
+
 CREATE FUNCTION historicize() RETURNS trigger
 AS $$
 BEGIN
     IF (TG_OP = 'INSERT') OR (TG_OP = 'UPDATE') THEN
-        EXECUTE format('INSERT INTO %I_history VALUES (DEFAULT, now(), txid_current(), False, $1.*)', TG_TABLE_NAME) USING NEW;
+        EXECUTE 'INSERT INTO history VALUES (DEFAULT, txid_current(), now()) ON CONFLICT DO NOTHING';
+        EXECUTE format('INSERT INTO %I_history VALUES (DEFAULT, txid_current(), False, $1.*)', TG_TABLE_NAME) USING NEW;
         RETURN NEW;
     ELSE
-        EXECUTE format('INSERT INTO %I_history VALUES (DEFAULT, now(), txid_current(), True, $1.*)', TG_TABLE_NAME) USING OLD;
+        EXECUTE 'INSERT INTO history VALUES (DEFAULT, txid_current(), now()) ON CONFLICT DO NOTHING';
+        EXECUTE format('INSERT INTO %I_history VALUES (DEFAULT, txid_current(), True, $1.*)', TG_TABLE_NAME) USING OLD;
         RETURN OLD;
     END IF;
 END;
 $$
 LANGUAGE plpgsql;
 
+--
+-- Entity with History
+--
+
 CREATE TABLE person (
     id serial PRIMARY KEY,
     name character varying(50) NOT NULL UNIQUE,
@@ -20,8 +36,7 @@ CREATE TABLE person (
 
 CREATE TABLE person_history (
     history_id serial PRIMARY KEY,
-    history_timestamp timestamp NOT NULL,
-    history_transaction bigint NOT NULL,
+    history_transaction bigint NOT NULL REFERENCES history(history_transaction),
     history_tombstone boolean NOT NULL,
     id integer NOT NULL,
     name character varying(50) NOT NULL,
@@ -30,37 +45,9 @@ 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;
+--
+-- Sample data
+--
 
 INSERT INTO person (name, email) VALUES ('michael', 'michael@hierweck.de');
 INSERT INTO person (name, email) VALUES ('annika', 'annika@hierweck.de');
@@ -80,3 +67,39 @@ 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;
+
+--
+-- Approach 1: Function
+--
+--
+-- Usage:
+--
+--        SELECT * FROM person_history(12345, 'name');
+--
+
+CREATE OR REPLACE FUNCTION person_history(transaction bigint, VARIADIC groupby text[]) RETURNS TABLE (
+    history_id integer,
+    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;
+
+--
+-- Approach 2: View
+--
+-- Usage:
+--
+--      SET history_transaction = 12345;
+--      SELECT * FROM person_history_view;
+--
+
+CREATE VIEW person_history_view
+AS (SELECT * FROM person_history WHERE history_id IN (SELECT max(history_id) AS history_id FROM person_history WHERE history_transaction <= current_setting('history.transaction')::bigint GROUP BY name));