resource.sql

-- Example of a postgre-driven immutable versioned and validated models

DROP TABLE orders CASCADE;
CREATE TABLE orders(
  id serial,                            -- Serial ID
  root_id integer,                      -- ID of a first version
  parent_id integer,                    -- ID of a previous version
  version integer,                      -- Version number
  errors jsonb,                         -- Results of validation

  created_at TIMESTAMP WITH TIME ZONE,  -- Initial creation time
  updated_at TIMESTAMP WITH TIME ZONE,  -- Last time of update
  deleted_at TIMESTAMP WITH TIME ZONE,  -- Datestamp of deletion (inherited)
  
  email varchar(255)                    -- GENERATED: column types
);

-- Scope: history of changes
CREATE OR REPLACE 
VIEW orders_versions AS 
SELECT * from orders WHERE errors is null ORDER BY root_id, version DESC;

-- Scope: last non-deleted versions 
CREATE OR REPLACE 
VIEW orders_current AS 
SELECT DISTINCT ON (root_id) * from orders_versions WHERE deleted_at is null;

-- find last version of an row
DROP FUNCTION order_head(integer, integer, boolean);
CREATE OR REPLACE FUNCTION order_head(integer, boolean DEFAULT true, integer DEFAULT 2147483646) RETURNS integer
    AS 'SELECT version from orders  WHERE root_id = $1 and version < $3 and 
       case when $2 then errors is null else true end 
       ORDER BY version DESC'
    LANGUAGE SQL
    IMMUTABLE
    RETURNS NULL ON NULL INPUT;

-- Inserts new version of a row
CREATE OR REPLACE FUNCTION
create_order() returns trigger language plpgsql AS $$ begin
  new.errors = '{}';
  
  -- GENERATED: column validations
  IF NOT new.email  ~ '^[^@]@.+\..+$' THEN
		SELECT jsonb_set(new.errors, '{email}', '"Email is incorrect"') into new.errors;
	END IF;

  -- fill created_at, start with 0 version and return errors
  return (
    new.id,
    coalesce(new.root_id, new.id),          -- inherit root_id or set to self
    new.parent_id,
    coalesce(new.version, 0),               -- start with 0 version unless given
    CASE WHEN new.errors::text != '{}' THEN -- pass validation errors if any
      new.errors
    END,
    coalesce(new.created_at, now()),        -- inherit or set creation timestamp
    new.updated_at,                         -- inherit modification timestamp
    new.deleted_at,                         -- inherit deletion timestamp
    new.email);                             -- GENERATED: column names
end $$;

CREATE TRIGGER create_order
    BEFORE INSERT ON orders
    FOR EACH ROW EXECUTE PROCEDURE create_order();

-- Turns update into insert and bumps version
CREATE OR REPLACE FUNCTION
update_order() returns trigger language plpgsql AS $$ begin
  INSERT INTO orders(
    root_id, parent_id, version, 
    created_at, updated_at, deleted_at,
    email)                                  -- GENERATED: column names
  VALUES (
    new.root_id,                            -- inherit root_id
    CASE WHEN new.parent_id is null and old.parent_id is not null THEN
      old.parent_id
    ELSE
      old.version
    END,
    order_head(old.root_id, false) + 1,            -- bump version to max + 1
    old.created_at,                         -- inherit creation timestamp 
    now(),                                  -- update modification timestamp
    new.deleted_at,                         -- inherit deletion timestamp
    new.email);                             -- GENERATED: column names

  return null;                              -- keep row immutable
end $$;

CREATE TRIGGER update_order
    BEFORE UPDATE ON orders
    FOR EACH ROW EXECUTE PROCEDURE update_order();


-- Turns DELETEs into INSERTS with deleted_at timestamp
CREATE OR REPLACE FUNCTION
delete_order() returns trigger language plpgsql AS $$
  declare
    prev integer :=  order_head(old.root_id, true, old.parent_id + 1);
  begin
    -- if deleting actual version or there is no valid previous version, set deleted_at timestamp
    if prev is null or ((order_head(old.root_id) = old.version and old.deleted_at is null) and old.parent_id = old.version - 1)    THEN
      EXECUTE 'UPDATE ' || TG_TABLE_NAME || ' SET deleted_at = now() WHERE id = $1' USING OLD.id;

    -- otherwise clone preceeding version without deletion flag and make it current
    ELSE
      UPDATE orders SET deleted_at=null,parent_id=null
      WHERE root_id = old.root_id and version=prev;
    END if;
      
    return null; -- dont delete original row
  end;
$$;

CREATE TRIGGER delete_order
    BEFORE DELETE ON orders
    FOR EACH ROW EXECUTE PROCEDURE delete_order();

-- Mark HEAD of an order as deleted (dont need to know version number)
CREATE OR REPLACE function
delete_current_order() returns trigger
language plpgsql
AS $$
	begin
	  DELETE from orders WHERE id=old.id;
    return null;
  end;
$$;

CREATE TRIGGER delete_current_order
    INSTEAD OF DELETE ON orders_current
    FOR EACH ROW EXECUTE PROCEDURE delete_current_order();

-- version 0 invalid  -- insert
INSERT into orders(email)  VALUES('a.com');
-- version 1 valid    -- update invalid to valid
UPDATE orders SET email='a@b.com' WHERE email='a.com';
-- version 2 invalid    -- update valid to invalid
UPDATE orders SET email='bbb' WHERE email='a@b.com';
-- version 3 valid    -- update invalid to valid
UPDATE orders SET email='a@c4.com' WHERE email='bbb';
-- version 4 deleted  -- soft delete head
DELETE from orders_current;
-- version 5 valid    -- undelete
DELETE from orders WHERE version=4;
-- version 6 valid    -- update email
UPDATE orders SET email=email ||'p' WHERE version=5;
-- version 7 valid    -- roll back to 3d version again
DELETE from orders WHERE version=4;
-- version 8 valid    -- roll back further to 1st, skip invalid 3nd
DELETE from orders_current;
-- version 9 deleted  -- no more valid version to roll back to, mark as deleted
DELETE from orders_current;
-- version 10 valid   -- undelete again
DELETE from orders WHERE version=(SELECT max(version) from orders);

INSERT into orders(email)  VALUES('a@c.com');
INSERT into orders(email)  VALUES('d.com');
SELECT * from orders_current;
-- 2 current valid orders
-- id | root_id | parent_id | version | created_at | updated_at | deleted_at |   email   |             errors              
-- ---+---------+-----------+---------+------------+------------+------------+-----------+ --------------------------------  
-- 11 |       1 |         0 |      10 | 25:48.4728 | 25:48.4808 |            | a@b.com   |                                 
-- 12 |      12 |           |       0 | 25:48.4815 |            |            | a@c.com   | 

SELECT * from orders ORDER BY id;
-- 10 versions + 1 + 1
-- id | root_id | parent_id | version | created_at | updated_at | deleted_at |   email   |             errors              
-- ---+---------+-----------+---------+------------+------------+------------+-----------+ --------------------------------
--  1 |       1 |           |       0 | 25:48.4728 |            |            | a.com     | {"email": "Email is incorrect"} 
--  2 |       1 |         0 |       1 | 25:48.4728 | 25:48.4738 |            | a@b.com   |                                 
--  3 |       1 |         1 |       2 | 25:48.4728 | 25:48.4752 |            | bbb       | {"email": "Email is incorrect"} 
--  4 |       1 |         2 |       3 | 25:48.4728 | 25:48.4761 |            | a@c4.com  |                                 
--  5 |       1 |         3 |       4 | 25:48.4728 | 25:48.4765 | 25:48.4765 | a@c4.com  |                                 
--  6 |       1 |         2 |       5 | 25:48.4728 | 25:48.4780 |            | a@c4.com  |                                 
--  7 |       1 |         5 |       6 | 25:48.4728 | 25:48.4787 |            | a@c4.comp |                                 
--  8 |       1 |         2 |       7 | 25:48.4728 | 25:48.4791 |            | a@c4.com  |                                 
--  9 |       1 |         0 |       8 | 25:48.4728 | 25:48.4796 |            | a@b.com   |                                 
-- 10 |       1 |         8 |       9 | 25:48.4728 | 25:48.4802 | 25:48.4802 | a@b.com   |                                 
-- 11 |       1 |         0 |      10 | 25:48.4728 | 25:48.4808 |            | a@b.com   |                                 
-- 12 |      12 |           |       0 | 25:48.4815 |            |            | a@c.com   |                                 
-- 13 |      13 |           |       0 | 25:48.4817 |            |            | d.com     | {"email": "Email is incorrect"}