sql 基于触发器的等效旧PostgreSQL时间旅行模块 - 请参阅http://blog.myitcv.org.uk/2014/02/25/row-level-version-control-wi

Posted 2021-05-13

/*
Copyright (c) 2015 Paul Jolly <[e-mail])

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

CREATE OR REPLACE FUNCTION process_timetravel_before() RETURNS TRIGGER AS $timetravel_before$
DECLARE
  temp_row RECORD; -- a temporary variable used on updates/deletes
  time_now TIMESTAMP; -- get the time now just once.... for consistency's sake
BEGIN
  time_now = now();

  IF (TG_OP = 'UPDATE' OR TG_OP = 'DELETE') THEN

    -- the user should not be able to update historic rows
    IF OLD.valid_to != 'infinity' THEN
      RAISE EXCEPTION 'Cannot % old row', TG_OP;
    END IF;

    -- use of TG_TABLE_NAME keeps this generic and non-table specific
    -- see http://www.postgresql.org/docs/9.3/static/plpgsql-statements.html#PLPGSQL-STATEMENTS-EXECUTING-DYN
    EXECUTE 'SELECT * FROM ' || TG_TABLE_NAME::regclass || ' WHERE ctid = $1 FOR UPDATE' USING OLD.ctid;

    -- not sure whether this is strictly required... could we modify OLD without side effects?
    temp_row := OLD;
    temp_row.valid_to := time_now;

    IF (TG_OP = 'UPDATE') THEN

      -- 'bump' the valid_from and ensure valid_to = 'infinity'
      NEW.valid_from := time_now;
      NEW.valid_to := 'infinity';

      -- allow the update to continue... so that the correct number of rows are reported
      -- as having been affected
      RETURN NEW;

    ELSIF (TG_OP = 'DELETE') THEN

      -- we want to allow the delete to continue... so that the correct number of rows are reported
      -- as having been affected
      RETURN OLD;

    END IF;

    RETURN NULL; -- shouldn't ever get here

  ELSIF (TG_OP = 'INSERT' AND NEW.valid_from is null OR NEW.valid_to is null) THEN

    -- this case could well be avoided by having a table definition with defaults:
    --
    --   valid_from = now()
    --   valid_to = 'infinity'
    --
    -- but we include this as a safety net
    IF NEW.valid_from is null THEN
      NEW.valid_from := time_now;
    END IF;
    IF NEW.valid_to is null THEN
      NEW.valid_to := 'infinity';
    END IF;

    -- allow the insert to continue... so that the correct number of rows are reported
    -- as having been affected
    RETURN NEW;

  ELSIF (TG_OP = 'INSERT') THEN

    -- allow the insert to continue... so that the correct number of rows are reported
    -- as having been affected
    RETURN NEW;

  END IF;

  RETURN NULL; -- won't get here if we only create the trigger for insert, update and delete

END;
$timetravel_before$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION process_timetravel_after() RETURNS TRIGGER AS $timetravel_after$
DECLARE
  temp_row RECORD; -- a temporary variable used on updates/deletes
  time_now TIMESTAMP; -- get the time now just once.... for consistency's sake
BEGIN
  time_now = now();

  IF (TG_OP = 'UPDATE' OR TG_OP = 'DELETE') THEN

    -- not sure whether this is strictly required... could we modify OLD without side effects?
    temp_row := OLD;
    IF (TG_OP = 'UPDATE') THEN
      temp_row.valid_to := NEW.valid_from;
    ELSIF (TG_OP = 'DELETE') THEN
      temp_row.valid_to := time_now;
    END IF;

    -- again, use of TG_TABLE_NAME keeps this generic and non-table specific
    EXECUTE 'INSERT INTO  ' || TG_TABLE_NAME::regclass || ' SELECT $1.*' USING temp_row;

  END IF;

  RETURN NULL; -- return value doesn't matter in after

END;
$timetravel_after$ LANGUAGE plpgsql;