在Codeigniter中添加mysql表之间的关系

Question

我使用Codeigniter，并希望在posts、和注释表之间添加关系。

帖子：

CREATE TABLE IF NOT EXISTS `posts` (
`post_id` int(5) unsigned NOT NULL AUTO_INCREMENT,
`title` varchar(100) COLLATE utf8_persian_ci NOT NULL,
`slug` varchar(100) COLLATE utf8_persian_ci NOT NULL,
`content` text COLLATE utf8_persian_ci NOT NULL,
`time` varchar(10) COLLATE utf8_persian_ci NOT NULL,
`num_of_comments` int(3) NOT NULL,
`cat` varchar(20) COLLATE utf8_persian_ci NOT NULL,
`tags` varchar(100) COLLATE utf8_persian_ci NOT NULL,
PRIMARY KEY (`post_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_persian_ci AUTO_INCREMENT=15 ;  

评论：

CREATE TABLE IF NOT EXISTS `comments` (
`id` int(3) NOT NULL AUTO_INCREMENT,
`content` text COLLATE utf8_persian_ci NOT NULL,
`date` varchar(100) COLLATE utf8_persian_ci NOT NULL,
`time` varchar(100) COLLATE utf8_persian_ci NOT NULL,
`name` varchar(20) COLLATE utf8_persian_ci NOT NULL,
`email` varchar(30) COLLATE utf8_persian_ci NOT NULL,
`image` varchar(20) COLLATE utf8_persian_ci NOT NULL,
`ip` varchar(16) COLLATE utf8_persian_ci NOT NULL,
`submit` int(1) NOT NULL,
`reply` text COLLATE utf8_persian_ci NOT NULL,
`reply_date` varchar(100) COLLATE utf8_persian_ci NOT NULL,
`reply_time` varchar(100) COLLATE utf8_persian_ci NOT NULL,
`post_id` int(5) unsigned NOT NULL,
PRIMARY KEY (`id`),
KEY `post_id` (`post_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_persian_ci AUTO_INCREMENT=26 ;  

但是它打印了这个错误：

SQL query:

ALTER TABLE  `comments` ADD FOREIGN KEY (  `post_id` ) REFERENCES  `codeig`.`posts` (

`post_id`
) ON DELETE CASCADE ON UPDATE CASCADE ;

MySQL said: 

#1452 - Cannot add or update a child row: a foreign key constraint fails (`codeig`.     <result 2 when explaining filename '#sql-fc8_dd'>, CONSTRAINT `#sql-fc8_dd_ibfk_1` FOREIGN  KEY (`post_id`) REFERENCES `posts` (`post_id`) ON DELETE CASCADE ON UPDATE CASCADE)  

我根本不知道在说什么。

请帮帮我..。

Answer 1

你在哪里写的这个查询？或者这是由代码点火器产生的？在任何sql管理工具中都可以这样做：

ALTER TABLE comments ADD FOREIGN KEY (post_id) REFERENCES posts(post_id) ON DELETE CASCADE ON UPDATE CASCADE ;

您不需要代码部分，我假设这是数据库名。