# Make mrbs_entry.repeat_id a foreign key

# Previously repeat_id was set to zero if there was no repeat.
# However this breaks our foreign key constraint so we have to modify
# the repeat_id column before we can create the foreign key.

/* Temporary copy of timestamp column */
ALTER TABLE %DB_TBL_PREFIX%entry
  ADD COLUMN saved_ts DATETIME;
UPDATE %DB_TBL_PREFIX%entry SET saved_ts=timestamp;

ALTER TABLE %DB_TBL_PREFIX%entry
  MODIFY COLUMN repeat_id int DEFAULT NULL;
  
UPDATE %DB_TBL_PREFIX%entry
  SET repeat_id=NULL WHERE repeat_id=0;

# Tidy up the database getting rid of any zombie rows which would prevent
# the foreign key being created.   Note that these rows will not be visible to users 
# and admins through MRBS.   They have most likely been created when a row has been
# deleted from a table using a database admin tool, rather than through MRBS.  Of course,
# foreign keys will stop this happening in the future.

DELETE FROM %DB_TBL_PREFIX%entry
  WHERE repeat_id IS NOT NULL
  AND repeat_id NOT IN (SELECT id FROM %DB_TBL_PREFIX%repeat);
  
DELETE FROM %DB_TBL_PREFIX%repeat
  WHERE id NOT IN (SELECT repeat_id FROM %DB_TBL_PREFIX%entry WHERE repeat_id IS NOT NULL);


ALTER TABLE %DB_TBL_PREFIX%entry
  ADD FOREIGN KEY (repeat_id) 
    REFERENCES %DB_TBL_PREFIX%repeat(id)
    ON UPDATE CASCADE
    ON DELETE CASCADE;

/* Put the table back to how it was */
UPDATE %DB_TBL_PREFIX%entry SET timestamp=saved_ts;
ALTER TABLE %DB_TBL_PREFIX%entry
  DROP COLUMN saved_ts;