记录关系很容易——您可以创建一个表foo_whatever (foo_id PK, whatever_set_id FK)
并仅为适当的 foo id 插入行。但是,该模式不会对您可以与任何集合关联的子类型实施任何约束,但您现有的模式也不会强制要求子类型是互斥的。可以使用相同的技术来强制执行两者。
考虑在所有表格上包括一个类型指示符foo_*
,例如使用enum('bar', 'baz', 'buz')
. 这提供了 in 中的子类型信息foo
(这可能比连接 3 个表来查找匹配更方便)并允许外键约束和检查约束强制执行独占子类型并限制可以记录在foo_whatever
. 是的,它涉及到一些冗余信息,但它很小并且没有更新异常的风险。
使用涉及类型指示符的复合外键约束,以及限制每个子类型表的类型指示符值的检查约束,应该可以解决问题。这是我建议的架构:
CREATE TABLE `foo` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`type` enum('bar','baz','buz') NOT NULL,
PRIMARY KEY (`id`),
KEY `foo_id` (`id`,`type`)
);
CREATE TABLE `foo_type_bar` (
`foo_id` int(11) NOT NULL,
`foo_type` enum('bar','baz','buz') NOT NULL CHECK (foo_type = 'bar'),
PRIMARY KEY (`foo_id`),
KEY `foo_bar_fk` (`foo_id`,`foo_type`),
CONSTRAINT `foo_bar_fk` FOREIGN KEY (`foo_id`, `foo_type`)
REFERENCES `foo` (`id`, `type`) ON DELETE CASCADE ON UPDATE CASCADE
);
CREATE TABLE `foo_type_baz` (
`foo_id` int(11) NOT NULL,
`foo_type` enum('bar','baz','buz') NOT NULL CHECK (foo_type = 'baz'),
PRIMARY KEY (`foo_id`),
KEY `foo_baz_fk` (`foo_id`,`foo_type`),
CONSTRAINT `foo_baz_fk` FOREIGN KEY (`foo_id`, `foo_type`)
REFERENCES `foo` (`id`, `type`) ON DELETE CASCADE ON UPDATE CASCADE
);
CREATE TABLE `foo_type_buz` (
`foo_id` int(11) NOT NULL,
`foo_type` enum('bar','baz','buz') NOT NULL CHECK (foo_type = 'buz'),
PRIMARY KEY (`foo_id`),
KEY `foo_buz_fk` (`foo_id`,`foo_type`),
CONSTRAINT `foo_buz_fk` FOREIGN KEY (`foo_id`, `foo_type`)
REFERENCES `foo` (`id`, `type`) ON DELETE CASCADE ON UPDATE CASCADE
);
CREATE TABLE `foo_whatever` (
`foo_id` int(11) NOT NULL,
`foo_type` enum('bar','baz','buz') NOT NULL CHECK (foo_type IN ('baz', 'buz')),
`whatever_set_id` int(11) NOT NULL,
PRIMARY KEY (`foo_id`),
KEY `whatever_foo_fk` (`foo_id`,`foo_type`),
KEY `whatever_set_fk` (`whatever_set_id`),
CONSTRAINT `whatever_foo_fk` FOREIGN KEY (`foo_id`, `foo_type`)
REFERENCES `foo` (`id`, `type`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `whatever_set_fk` FOREIGN KEY (`whatever_set_id`)
REFERENCES `whatever_set` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
);
但是,由于 MySQL 忽略了检查约束,因此您需要使用触发器来实现相同的目的:
DELIMITER ;;
CREATE TRIGGER foo_bar_insert_type_check
BEFORE INSERT ON foo_type_bar
FOR EACH ROW
BEGIN
IF NEW.foo_type != 'bar' THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'Invalid foo_type in foo_type_bar';
END IF;
END;;
CREATE TRIGGER foo_bar_update_type_check
BEFORE UPDATE ON foo_type_bar
FOR EACH ROW
BEGIN
IF NEW.foo_type != 'bar' THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'Invalid foo_type in foo_type_bar';
END IF;
END;;
CREATE TRIGGER foo_baz_insert_type_check
BEFORE INSERT ON foo_type_baz
FOR EACH ROW
BEGIN
IF NEW.foo_type != 'baz' THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'Invalid foo_type in foo_type_baz';
END IF;
END;;
CREATE TRIGGER foo_baz_update_type_check
BEFORE UPDATE ON foo_type_baz
FOR EACH ROW
BEGIN
IF NEW.foo_type != 'baz' THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'Invalid foo_type in foo_type_baz';
END IF;
END;;
CREATE TRIGGER foo_buz_insert_type_check
BEFORE INSERT ON foo_type_buz
FOR EACH ROW
BEGIN
IF NEW.foo_type != 'buz' THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'Invalid foo_type in foo_type_buz';
END IF;
END;;
CREATE TRIGGER foo_buz_update_type_check
BEFORE UPDATE ON foo_type_buz
FOR EACH ROW
BEGIN
IF NEW.foo_type != 'buz' THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'Invalid foo_type in foo_type_buz';
END IF;
END;;
CREATE TRIGGER foo_whatever_insert_type_check
BEFORE INSERT ON foo_whatever
FOR EACH ROW
BEGIN
IF NEW.foo_type NOT IN ('baz', 'buz') THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'Invalid foo_type in foo_whatever';
END IF;
END;;
CREATE TRIGGER foo_whatever_update_type_check
BEFORE UPDATE ON foo_whatever
FOR EACH ROW
BEGIN
IF NEW.foo_type NOT IN ('baz', 'buz') THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'Invalid foo_type in foo_whatever';
END IF;
END;;
DELIMITER ;