@@ -28,10 +28,77 @@ being deleted to null), triggered table column names which correspond
2828to primary/unique key, referencing table name and column names corresponding
2929to foreign key (, ... - as many referencing tables/keys as specified
3030by first argument).
31- Note, that NOT NULL constraint and unique index have to be defined
32- by youself.
31+ Note, that NOT NULL constraint and unique index have to be defined by
32+ youself.
3333
34- There are examples in refint.example and regression tests
34+ There are examples in refint.example and regression tests
3535(sql/triggers.sql).
3636
37+ To CREATE FUNCTIONs use refint.sql (will be made by gmake from
38+ refint.source).
3739
40+
41+ 2. timetravel.c - functions for implementing time travel feature.
42+
43+ Old internally supported time-travel (TT) used insert/delete
44+ transaction commit times. To get the same feature using triggers
45+ you are to add to a table two columns of abstime type to store
46+ date when a tuple was inserted (start_date) and changed/deleted
47+ (stop_date):
48+
49+ CREATE TABLE XXX (
50+ ......
51+ date_onabstime default currabstime(),
52+ date_offabstime default 'infinity'
53+ ......
54+ );
55+
56+ - so, tuples being inserted with NULLs in date_on/date_off will get
57+ _current_date_ in date_on (name of start_date column in XXX) and INFINITY in
58+ date_off (name of stop_date column in XXX).
59+
60+ Tuples with stop_date equal INFINITY are "valid now": when trigger will
61+ be fired for UPDATE/DELETE of a tuple with stop_date NOT equal INFINITY then
62+ this tuple will not be changed/deleted!
63+
64+ If stop_date equal INFINITY then on
65+
66+ UPDATE: only stop_date in tuple being updated will be changed to current
67+ date and new tuple with new data (coming from SET ... in UPDATE) will be
68+ inserted. Start_date in this new tuple will be setted to current date and
69+ stop_date - to INFINITY.
70+
71+ DELETE: new tuple will be inserted with stop_date setted to current date
72+ (and with the same data in other columns as in tuple being deleted).
73+
74+ NOTE:
75+ 1. To get tuples "valid now" you are to add _stop_date_ = 'infinity'
76+ to WHERE. Internally supported TT allowed to avoid this...
77+ Fixed rewriting RULEs could help here...
78+ As work arround you may use VIEWs...
79+ 2. You can't change start/stop date columns with UPDATE!
80+ Use set_timetravel (below) if you need in this.
81+
82+ FUNCTIONs:
83+
84+ timetravel() is general trigger function.
85+
86+ You are to create trigger BEFORE (!!!) UPDATE OR DELETE using this
87+ function on a time-traveled table. You are to specify two arguments: name of
88+ start_date column and name of stop_date column in triggered table.
89+
90+ currabstime() may be used in DEFAULT for start_date column to get
91+ current date.
92+
93+ set_timetravel() allows you turn time-travel ON/OFF for a table:
94+
95+ set_timetravel('XXX', 1) will turn TT ON for table XXX (and report
96+ old status).
97+ set_timetravel('XXX', 0) will turn TT OFF for table XXX (-"-).
98+
99+ Turning TT OFF allows you do with a table ALL what you want.
100+
101+ There is example in timetravel.example.
102+
103+ To CREATE FUNCTIONs use timetravel.sql (will be made by gmake from
104+ timetravel.source).