Table that keeps its own history, SQLite

1_sqlite_table_with_history.ddl

/*
Database schema SQLite for a table that keeps its own history and 
never deletes data. 

On update, historic data is kept under a new id and references the original
creation id. The end of life timestamp (ts_eol) is set so a time line can be
built. The new data is used to update the data under the existing id.

On delete, nothing is deleted. Only the ts_eol timestamp is set to current.
*/

DROP TABLE IF EXISTS Trigger;
DROP TABLE IF EXISTS Keep;
DROP VIEW IF EXISTS view_Keep;


/* 
The table that keeps its own history. ts_eol and hist_id are used to keep history plus
one column with a partial index.
 */
CREATE TABLE IF NOT EXISTS Keep(
          id INTEGER PRIMARY KEY NOT NULL,
          -- start data block
      person TEXT NOT NULL,   -- part of partial index pidx_person_eol
       asset TEXT NOT NULL,
     ts_from TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP, -- is not required for keeping history
          -- ....
          -- ....
          -- end datablock
      ts_eol TEXT DEFAULT NULL,
     hist_id INTEGER DEFAULT NULL REFERENCES Keep(id),
  CONSTRAINT id_not_historic CHECK(id <> hist_id)
);

CREATE UNIQUE INDEX pidx_person_eol
    ON Keep(person) 
 WHERE ts_eol IS NULL
;
--CREATE INDEX historic_idx 
--    ON Keep(hist_id)
--;


/* 
the view to run the updates and deletes against 
*/
CREATE VIEW IF NOT EXISTS view_Keep
    AS
SELECT id, person, asset, ts_from,ts_eol, hist_id  -- *
  FROM Keep
 WHERE ts_eol IS NULL
;


-- the below has to be created on (writer) connection to the db.

/* 
The temp table holds a flag that makes it possible to directy update the Keep table.
When FALSE direct updates are not possible. 
*/
CREATE TEMP TABLE IF NOT EXISTS Trigger(
  trigger_on TEXT NOT NULL UNIQUE,
       state BOOL CHECK(state IN (FALSE, TRUE))
);
INSERT INTO Trigger(trigger_on, state)
VALUES ('insert_keep', FALSE)
;


/* 
trigger to prevent updates directly to the Keep table 
*/
CREATE TEMP TRIGGER IF NOT EXISTS before_update_Keep
BEFORE UPDATE 
    ON main.Keep
  WHEN (
       SELECT state 
         FROM Trigger 
        WHERE trigger_on = 'insert_keep'
       ) = FALSE 
 BEGIN 
       SELECT RAISE(FAIL,'ERROR! Cannot update directly to Keep. Update to view_Keep');
   END
;


/*
trigger to update the Keep table. The insert_keep flag has to be set 
to TRUE before the update or else the before_update_Keep trigger will kick in.
*/
 CREATE TEMP TRIGGER IF NOT EXISTS update_view_Keep
INSTEAD OF UPDATE 
     ON view_Keep
  BEGIN 
        UPDATE Trigger
           SET state = TRUE
         WHERE trigger_on = 'insert_keep'
        ;
        
        UPDATE Keep
           SET asset = new.asset, ts_from = CURRENT_TIMESTAMP 
         WHERE person = old.person AND old.ts_eol IS NULL
        ;

        UPDATE Trigger
          SET state = FALSE
        WHERE trigger_on = 'insert_keep'
        ;
        
        INSERT INTO Keep (person, asset, hist_id, ts_from, ts_eol)
        SELECT old.person, old.asset, old.id, old.ts_from, CURRENT_TIMESTAMP
        ; 
    END
;


/* 
trigger to prevent deletes directly to the Keep table 
*/
CREATE TEMP TRIGGER IF NOT EXISTS before_delete_Keep
BEFORE DELETE 
    ON main.Keep
 BEGIN 
       SELECT RAISE(FAIL,'ERROR! Cannot delete directly from Keep. Delete from view_Keep');
   END
;


/*
trigger to "delete" from the Keep table. The insert_keep flag has to be set 
to TRUE before the update or else the before_update_Keep trigger will kick in.
*/
 CREATE TEMP TRIGGER IF NOT EXISTS delete_view_Keep
INSTEAD OF DELETE
     ON view_Keep
  BEGIN
        UPDATE Trigger
           SET state = TRUE
         WHERE trigger_on = 'insert_keep'
        ;
                
        UPDATE Keep
           SET ts_eol = CURRENT_TIMESTAMP
         WHERE id = old.id
           AND ts_eol IS NULL
           AND hist_id IS NULL
        ;
        
        UPDATE Trigger
          SET state = FALSE
        WHERE trigger_on = 'insert_keep'
        ;
    END
;

2_sqlite_query_table_with_history.sql

/*    
    Al die willen te kaap'ren varen
    Moeten mannen met baarden zijn
    Jan, Pier, Tjores en Corneel
    Die hebben baarden, die hebben baarden
    Jan, Pier, Tjores en Corneel
    Die hebben baarden, zij varen mee
*/


-- writer queries

INSERT INTO Keep(person, asset)
VALUES ('jan', 'baard'), ('pier', 'baard'), ('tjoris', 'baard'), ('corneel', 'baard')
;


UPDATE view_Keep
   SET asset = 'glad'
 WHERE person = 'corneel'
;

UPDATE view_Keep
   SET asset = 'bakkebaard'
 WHERE person = 'jan'
;

UPDATE view_Keep
   SET asset = 'glad'
 WHERE person = 'pier'
;

UPDATE view_Keep
   SET asset = 'soul patch'
 WHERE person = 'corneel'
;


DELETE FROM view_Keep
 WHERE person = 'corneel'
;


-- transaction to reinstate a deleted person

BEGIN TRANSACTION

INSERT INTO Keep (person, asset, hist_id, ts_from, ts_eol)
SELECT person, asset, id, ts_from, CURRENT_TIMESTAMP
  FROM KEEP
 WHERE person = 'corneel' 
   AND ts_eol IS NOT NULL 
   AND hist_id IS NULL  
;

UPDATE Trigger
   SET state = TRUE
 WHERE trigger_on = 'insert_keep'
;
        
UPDATE Keep
   SET ts_eol = NULL, ts_from = CURRENT_TIMESTAMP 
 WHERE person = 'corneel' 
   AND ts_eol IS NOT NULL 
   AND hist_id IS NULL
;

UPDATE Trigger
   SET state = FALSE
 WHERE trigger_on = 'insert_keep'
;

ROLLBACK;    


-- Reader queries

SELECT *
  FROM Keep
 WHERE person = 'corneel'
-- AND hist_id IS NOT NULL
;

/*history length*/
SELECT person, count(id)
  FROM Keep
 WHERE person = 'corneel'
;

/*history since*/
SELECT person, count(id), min(ts_from) AS since
  FROM Keep
 WHERE person = 'corneel'
;

/*sql to get deleted id's*/
SELECT id, person, asset, ts_from, ts_eol
  FROM Keep
    -- a deleted item / item timeline, has a set ts_eol, but no hist_id.
 WHERE ts_eol IS NOT NULL
   AND hist_id IS NULL  
;