如何处理具有排除约束的表的更新？

Question

我有一个表格来跟踪带有排除约束的酒店预订，如下所示。

目前，我允许客人更新他们的预订。因此，如果 guest_id 1 将他的预订从 3 天预订更改为从 2010-01-03、2010-01-03 开始​​的一天，如果我运行此更新语句，postgres 将由于重叠约束而阻止更新：

update reservation set from_ts = '2021-01-03 00:00:00', to_ts='2021-01-10 23:59:00', during = '[2021-01-03 00:00:00, 2021-01-10 23:59:00]' where id = 1

那么您如何允许此更新？您是否必须保持预订 id 相同，并删除其他的？

** 注意：我实际上是每行存储一天，因为我还有其他属性可以每天跟踪**

Table: reservation
 id | room |  from_ts            |   to_ts             | guest_id
----+------+---------------------+---------------------+------------
  1 |  101 | 2010-01-01 00:00:00 | 2010-01-01 23:59:00 | 1
  2 |  101 | 2010-01-02 00:00:00 | 2010-01-02 23:59:00 | 1
  3 |  101 | 2010-01-03 00:00:00 | 2010-01-03 23:59:00 | 1

CREATE TABLE reservation (
    id int,
    guest_id int,
    room int,
    from_ts timestamp without time zone,
    to_ts timestamp without time zone,
    during tsrange,
    EXCLUDE USING GIST (room WITH =, during WITH &&)
);
-- bootstrap to test the problem
INSERT INTO reservation ( id, guest_id, room, from_ts, to_ts, during ) VALUES ( 1, 1, 101, '2021-01-01 00:00:00', '2021-01-01 23:59:00', '[2021-01-01 00:00:00, 2021-01-01 23:59:00]');
INSERT INTO reservation ( id, guest_id, room, from_ts, to_ts, during ) VALUES ( 2, 1, 101, '2021-01-02 00:00:00', '2021-01-02 23:59:00', '[2021-01-02 00:00:00, 2021-01-02 23:59:00]' );
INSERT INTO reservation ( id, guest_id, room, from_ts, to_ts, during ) VALUES ( 3, 1, 101, '2021-01-03 00:00:00', '2021-01-03 23:59:00', '[2021-01-03 00:00:00, 2021-01-03 23:59:00]' );

-- update statement will fail after you run the insert statements
update reservation set from_ts = '2021-01-03 00:00:00', to_ts='2021-01-10 23:59:00', during = '[2021-01-03 00:00:00, 2021-01-10 23:59:00]' where id = 1

Answer 1

您可以通过使用不同的排除约束而不是您创建的排除约束来解决该问题：

ALTER TABLE reservation ADD EXCLUDE USING gist (
   room WITH =,
   guest_id WITH <>,
   tsrange(from_ts, to_ts, '[]') WITH &&
);

这将排除两个房间相等的条目并且时间戳范围重叠并且预订是针对不同的客人。

请注意，我使用的是表达式而不是 during。避免数据库设计中的冗余是一个好主意。当然你也可以保留duration，去掉from_ts和to_ts。

还要注意to_ts 的尴尬程度，在 23:59:00 结束。您可以改为选择在上端开放的区间：

SELECT tsrange('2021-01-02 00:00:00', '2021-01-03 00:00:00');

                    tsrange                    
═══════════════════════════════════════════════
 ["2021-01-02 00:00:00","2021-01-03 00:00:00")
(1 row)

这不会与以 2021-01-03 00:00:00 开头的范围重叠。