[英]how to handle updates on a table with exclusion constraint?
I have a table keep track of hotel reservations with exclusion constraint like below.我有一个表格来跟踪酒店预订情况,如下所示。
Currently, I allow guests to update their reservations.目前,我允许客人更新他们的预订。 So if guest_id 1 change his reservation from 3 day reservation to a single day from 2010-01-03, 2010-01-03, postgres will block the update due to the overlap constraint if i ran the this update statement:
因此,如果 guest_id 1 从 2010-01-03、2010-01-03 将他的预订从 3 天预订更改为一天,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
How do you go about allowing this update then?你怎么go关于允许这个更新呢? Do you have to keep the reservation id the same, and delete the others?
您是否必须保持预订 ID 不变,并删除其他的?
** note: I'm actually storing a day per row as I have other attributes to keep track at per day basis ** ** 注意:我实际上每行存储一天,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
You can solve that problem by using a different exclusion constraint instead of the one you created: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 &&
);
That will exclude two entries where the room is equal and the timstamp ranges overlap and the reservation is for different guests.这将排除两个条目,其中房间相同且时间戳范围重叠并且预订是针对不同客人的。
Note that I used an expression rather than during
.请注意,我使用了一个表达式而不是
during
。 It is a good idea to avoid redundancy in database design.在数据库设计中避免冗余是个好主意。 You can of course also keep the
duration
and do away with from_ts
and to_ts
.您当然也可以保留
duration
并取消from_ts
和to_ts
。
Also note how awkward to_ts
is, ending at 23:59:00.还要注意
to_ts
在 23:59:00 结束时有多尴尬。 You may instead choose intervals that are open at the upper end:您可以改为选择在上端开放的间隔:
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)
This won't overlap with a range that starts with 2021-01-03 00:00:00.这不会与以 2021-01-03 00:00:00 开头的范围重叠。
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