MySQL with InnoDB revision control rows

Question

I would like to have a way of controlling/tracking revisions of rows. I am trying to find the best solution for this problem.

The first thing that comes to mind is to have a table with a id to identify the row and and id for the revision number. The combined ids would be the primary key. so example data might look like this:

1, 0, "original post" 1, 1, "modified post" 1, 2, "modified again post"

How can I create a table with this behavior? or is there a better solution to do this?

I like InnoDB since it supports transactions, foreign keys and full text in MySQL 5.6+.

I know its possible to "force" this behavior by how I insert the data but I'm wondering if there is a way to have the table do this automatically.

Answer 1

Consider table structure:

TABLE posts
  post_id INT AUTO_INCREMENT PK
  cur_rev_id INT FK(revisions.rev_id)

TABLE revisions
  rev_id INT AUTO_INCREMENT PK
  orig_post INT FK(posts.post_id)
  post_text VARCHAR

Where the posts table tracks non-versioned information about the post and its current revision, and revisions tracks each version of the post text with a link back to the parent post. Because of the circular FK constraints you'd need to enclose new post insertions in a transaction.

With this you should be able to easily add, remove, track, roll back, and preview revisions to your posts.

Edit:

Yeah, enclosing in a transaction won't exactly help since the keys are set to AUTO_INCREMENT , so you need to dip back in to PHP with LAST_INSERT_ID() and some temporarily NULL indexes.

CREATE TABLE `posts` (
    `post_id` INT(10) NOT NULL AUTO_INCREMENT,
    `cur_rev_id` INT(10) NULL DEFAULT NULL,
    `post_title` VARCHAR(50) NULL DEFAULT NULL,
    PRIMARY KEY (`post_id`),
    INDEX `FK_posts_revisions` (`cur_rev_id`),
) ENGINE=InnoDB

CREATE TABLE `revisions` (
    `rev_id` INT(10) NOT NULL AUTO_INCREMENT,
    `orig_post` INT(10) NULL DEFAULT NULL,
    `post_text` VARCHAR(32000) NULL DEFAULT NULL,
    PRIMARY KEY (`rev_id`),
    INDEX `FK_revisions_posts` (`orig_post`),
) ENGINE=InnoDB

ALTER TABLE `posts`
    ADD CONSTRAINT `FK_posts_revisions` FOREIGN KEY (`cur_rev_id`) REFERENCES `revisions` (`rev_id`);
ALTER TABLE `revisions`
    ADD CONSTRAINT `FK_revisions_posts` FOREIGN KEY (`orig_post`) REFERENCES `posts` (`post_id`);

Then:

$db_engine->query("INSERT INTO posts (cur_rev_id, post_title) VALUES (NULL, 'My post Title!')");
$post_id = $db_engine->last_insert_id();

$db_engine->query("INSERT INTO revisions (orig_post, post_text) VALUES($post_id, 'yadda yadda')");
$rev_id = $db_engine->last_insert_id();

$db_engine->query("UPDATE posts SET cur_rev_id = $rev_id WHERE post_id = $post_id");

Answer 2

If I've understood you correctly and the table doesn't receive large numbers of updates/deletes then you could look at setting a trigger such as:

DELIMITER $$
CREATE TRIGGER t_table_update BEFORE UPDATE ON table_name
FOR EACH ROW
    INSERT INTO table_name_revisions (item_id, data, timestamp) 
        VALUES(OLD.id, OLD.data, NOW());
END$$
DELIMITER ;

See trigger syntax for more information