history.log_change.sql

 CREATE OR REPLACE FUNCTION history.log_change() RETURNS trigger AS $_$
     DECLARE
       c refcursor;
       tt tstzrange;
       r record;
       str text;
       my_new text;
     BEGIN
        str := '';
        my_new := '';
        FOR r IN SELECT (each(hstore(NEW))).* 
        LOOP
       	  RAISE NOTICE '% value is %', r.key, quote_nullable(r.value);
     	  str :=  str || ',' || r.key;   	      
     	  my_new :=  my_new || ',$1.' || r.key;   	      
        END LOOP;
             str :=  SUBSTRING(str FROM 2);
             my_new :=  SUBSTRING(my_new FROM 2);
       	  RAISE NOTICE 'str: %', str;
       	  RAISE NOTICE 'my_new: %', my_new;
         IF TG_OP = 'INSERT' THEN
--            RAISE NOTICE 'SELECT % from %', str,  NEW;
             EXECUTE 'INSERT INTO history.' || TG_TABLE_NAME || ' (_validrange, ' || str || ' )'
               ' SELECT tstzrange(now(), $$infinity$$, $$[)$$), '|| my_new ||'' USING NEW;
             RETURN NEW;
         ELSIF TG_OP = 'UPDATE' THEN
             OPEN c FOR EXECUTE 'SELECT _validrange FROM history.' || TG_TABLE_NAME ||
               ' WHERE id = $1 ORDER BY _validrange DESC LIMIT 1 FOR UPDATE'
               USING NEW.id;
             FETCH FROM c INTO tt;

             IF isempty(tstzrange(lower(tt), now(), $$[)$$)) THEN
                EXECUTE 'DELETE FROM history.' || TG_TABLE_NAME ||
                   ' WHERE CURRENT OF ' || quote_ident(c::text);
             ELSE
                 EXECUTE 'UPDATE history.' || TG_TABLE_NAME || ' SET _validrange = tstzrange($1, now(), $$[)$$)' ||
                   ' WHERE CURRENT OF ' || quote_ident(c::text) USING lower(tt);
             END IF;

             EXECUTE 'INSERT INTO history.' || TG_TABLE_NAME || ' (_validrange, ' || str || ' )'
               ' SELECT tstzrange(now(), $$infinity$$, $$[)$$), '|| my_new ||'' USING NEW;

             RETURN NEW;
         ELSIF TG_OP = 'DELETE' THEN

           OPEN c FOR EXECUTE 'SELECT _validrange FROM history.' || TG_TABLE_NAME ||
             ' WHERE id = $1 ORDER BY _validrange DESC LIMIT 1 FOR UPDATE' USING OLD.id;

           FETCH FROM c into tt;

           IF isempty(tstzrange(lower(tt), now(), $$[)$$)) THEN
             EXECUTE 'DELETE FROM history.' || TG_TABLE_NAME ||
               ' WHERE CURRENT OF ' || quote_ident(c::text);
             RETURN OLD;
           END IF;

           EXECUTE 'UPDATE history.' || TG_TABLE_NAME ||
             ' SET _validrange = tstzrange($1, now(), $$[)$$) WHERE CURRENT OF ' ||
             quote_ident(c::text) USING lower(tt);

           RETURN OLD;
         END IF;
         RETURN NULL;
     END;
 $_$ LANGUAGE plpgsql;