Deleting correct in a many-to-many relationship - mysql

Question

I've got a short question with a many-to-many relationship.
Here are my tables:
+---------+----------------+
| film_id | title |
+---------+----------------+
| 1 | Apocalypse Now |
+---------+----------------+
+-------------+----------------------+
| category_id | name |
+-------------+----------------------+
| 1 | cool category |
+-------------+----------------------+
| 2 | not so cool category |
+-------------+----------------------+
+---------+-------------+
| film_id | category_id |
+---------+-------------+
| 1 | 1 |
+---------+-------------+
| 1 | 2 |
+---------+-------------+
As you can see there are FKs from the film- and category-table in the film_category-table.
What I want: If one wants to delete a category, then ALL entries in the film_category where the category_id occurs should be deleted, too. BUT not the related films! In addition to that: This should work while deleting a film vice versa! (That's exactly my problem here)
My Question: Can I solve the issue with a FK-definition only or do I have to delete all entries in the film_category-table manually before deleting a film or category?

Answer 1

Your tables should look something like the following. A delete in the film table should delete the rows where the film category has the same id, and vice versa with the film table.
CREATE TABLE `film` (
`film_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`title` varchar(255) NOT NULL DEFAULT '',
PRIMARY KEY (`film_id`)
) ENGINE=InnoDB;
CREATE TABLE `category` (
`category_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL DEFAULT '',
PRIMARY KEY (`category_id`)
) ENGINE=InnoDB;
CREATE TABLE `film_category` (
`film_category_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`film_id` int(10) unsigned NOT NULL DEFAULT '0',
`category_id` int(10) unsigned NOT NULL DEFAULT '0',
PRIMARY KEY (`film_category_id`),
KEY `film_id` (`film_id`),
KEY `category_id` (`category_id`),
CONSTRAINT `film_category_ibfk_2` FOREIGN KEY (`category_id`) REFERENCES `category` (`category_id`) ON DELETE CASCADE,
CONSTRAINT `film_category_ibfk_1` FOREIGN KEY (`film_id`) REFERENCES `film` (`film_id`) ON DELETE CASCADE
) ENGINE=InnoDB;
You should also be able to use the following for film_category:
CREATE TABLE `film_category` (
`film_id` int(10) unsigned NOT NULL DEFAULT '0',
`category_id` int(10) unsigned NOT NULL DEFAULT '0',
PRIMARY KEY (`film_id`,`category_id`),
CONSTRAINT `film_category_ibfk_1` FOREIGN KEY (`film_id`) REFERENCES `film` (`film_id`) ON DELETE CASCADE,
CONSTRAINT `film_category_ibfk_2` FOREIGN KEY (`category_id`) REFERENCES `category` (`category_id`) ON DELETE CASCADE
) ENGINE=InnoDB;