MariaDB“在更新级联”约束不能按预期工作？

Question

我原以为ON UPDATE CASCADE约束将允许我更新引用外键的值，并将其级联到它的裁判员(就像在PostgreSQL中那样)，但情况似乎并非如此。

我漏掉了什么吗？

这里使用MariaDB 10.3.29-MariaDB-0ubuntu0.20.04.1

CREATE TABLE category (
  id int(11) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  parent_id int(11) UNSIGNED DEFAULT NULL,
  slug varchar(255) NOT NULL,
  title varchar(255) NOT NULL,
  content longtext NOT NULL,
  created_at datetime NOT NULL DEFAULT current_timestamp(),
  updated_at datetime DEFAULT NULL,
  CONSTRAINT fk_category_parent_id FOREIGN KEY (parent_id) REFERENCES category (id) ON DELETE RESTRICT ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;


INSERT INTO `category` (`id`, `parent_id`, `slug`, `title`, `content`, `created_at`, `updated_at`) VALUES
(1, NULL, 'non-classe', 'Non Classé', '', '2021-05-30 16:46:52', NULL),
(2, NULL, 'cours', 'Cours', '', '2021-05-30 16:47:38', NULL),
(3, 2, 'mysql', 'MySQL', '', '2021-05-30 16:48:18', NULL),
(4, 3, 'initiation-mysql', 'Cours initiation MySQL', '', '2021-05-30 16:49:09', NULL);

UPDATE category SET id = 12 WHERE id = 2;
-- ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`cours_cms`.`category`, CONSTRAINT `fk_category_parent_id` FOREIGN KEY (`parent_id`) REFERENCES `category` (`id`) ON UPDATE CASCADE)

Answer 1

请参阅本页的评论：

https://mariadb.com/kb/en/foreign-keys/

--如果在UPDATE级联上递归更新以前在级联期间更新过的表，则它的作用类似于限制。这意味着不能在更新级联操作中使用自引用。这是为了防止由级联更新导致的无限循环。

换句话说，如果更新级联是一个层次数据类型的表，那么它就不能工作。

Answer 2

只是在没有“无限循环”的PostgreSQL中确认了这一点。

CREATE TABLE category (
  id SERIAL PRIMARY KEY,
  parent_id int DEFAULT NULL,
  slug varchar(255) NOT NULL,
  title varchar(255) NOT NULL,
  content text NOT NULL,
  CONSTRAINT fk_category_parent_id FOREIGN KEY (parent_id) REFERENCES category (id) ON DELETE RESTRICT ON UPDATE CASCADE
);

INSERT INTO category (id, parent_id, slug, title, content) VALUES
(1, NULL, 'non-classe', 'Non Classé', ''),
(2, NULL, 'cours', 'Cours', ''),
(3, 2, 'mysql', 'MySQL', ''),
(4, 3, 'initiation-mysql', 'Cours initiation MySQL', '');

UPDATE category SET id=12 WHERE id=2;

SELECT * FROM category;
 id | parent_id |       slug       |         title          | content 
----+-----------+------------------+------------------------+---------
  1 |           | non-classe       | Non Classé             | 
  4 |         3 | initiation-mysql | Cours initiation MySQL | 
 12 |           | cours            | Cours                  | 
  3 |        12 | mysql            | MySQL                  |