[DDC-881] DDC-117: Linked Objects with composite key

Sun, 2 Jan 2011 06:05:12 +0000

I'm currently playing around with ~~DDC-117~~. I came across a general
problem which occurs with relations.

Given the following two classes, should a
@OneToOne/@OneToMany/@ManyToMany relation consider a composite ID or is
that not planned with ~~DDC-117~~?

In the past, we assumed that an object is identified unique with an @Id
column. However, if we support composite keys, an object needs to be
identified by two or more columns, which we need to take into
consideration when building queries and foreign keys. Is that correct?

/**
 * @Entity
 */

class Document {
	/**
	 * @Id
	 * @Column(type="integer")
	 * @GeneratedValue(strategy="AUTO")
	 */
	private $id;

	/**
	 * @Id
	 * @Column(type="integer")
	 */
	private $version;

	/**
	 * @ManyToOne(targetEntity="Content")
	 * Enter description here ...
	 * @var unknown_type
	 */
	private $content;
}

/**
 * @Entity
 */
class Content {
	/**
	 * @Id
	 * @Column(type="integer")
	 * @GeneratedValue(strategy="AUTO")
	 */
	private $id;

	/**
	 * @Id
	 * @Column(type="integer")
	 */
	private $version;

	/**
	 * @ManyToOne(targetEntity="Document")
	 */

	private $document;
}

I know this might become a bit tricky, because $content refers to a
single instance of Content, but we actually need two columns to identify
it. That's how it looks if generated with Doctrine2 (~~DDC-117~~):

mysql> describe Document;
+------------+---------+------+-----+---------+-------+
| Field      | Type    | Null | Key | Default | Extra |
+------------+---------+------+-----+---------+-------+
| id         | int(11) | NO   | PRI | NULL    |       |
| version    | int(11) | NO   | PRI | NULL    |       |
| content_id | int(11) | YES  | MUL | NULL    |       |
+------------+---------+------+-----+---------+-------+

mysql> describe Content;
+-------------+---------+------+-----+---------+-------+
| Field       | Type    | Null | Key | Default | Extra |
+-------------+---------+------+-----+---------+-------+
| id          | int(11) | NO   | PRI | NULL    |       |
| version     | int(11) | NO   | PRI | NULL    |       |
| document_id | int(11) | YES  | MUL | NULL    |       |
+-------------+---------+------+-----+---------+-------+

However, to make my example work, the tables would need to look the
following:

mysql> describe Content;
+------------------+---------+------+-----+---------+-------+
| Field            | Type    | Null | Key | Default | Extra |
+------------------+---------+------+-----+---------+-------+
| id               | int(11) | NO   | PRI | NULL    |       |
| version          | int(11) | NO   | PRI | NULL    |       |
| document_id      | int(11) | YES  | MUL | NULL    |       |
| document_version | int(11) | YES  |     | NULL    |       |
+------------------+---------+------+-----+---------+-------+

mysql> describe Document;
+-----------------+---------+------+-----+---------+-------+
| Field           | Type    | Null | Key | Default | Extra |
+-----------------+---------+------+-----+---------+-------+
| id              | int(11) | NO   | PRI | NULL    |       |
| version         | int(11) | NO   | PRI | NULL    |       |
| content_id      | int(11) | YES  | MUL | NULL    |       |
| content_version | int(11) | YES  |     | NULL    |       |
+-----------------+---------+------+-----+---------+-------+

It would be nice if we could discuss this one, as I feel it is important for an ORM.

Doctrine Project

[DDC-881] DDC-117: Linked Objects with composite key