5.2. Model relationships

Relationships between your Models are defined using the ModelRelation::define() method. For example:

ModelRelation::define('Person(1):Pet(M)');
ModelRelation::define('Book(M):Author(M)');
ModelRelation::define('Category(M):CategoryLinks.left_id.right_id(1):Category(M)');

See the API documentation for more details on the complexities of this powerful function.

1:M

Definition examples:

ModelRelation::define('House(1):Window(M)');			/* Presumes "window.house_id" FK */
ModelRelation::define('Human(1):Limb.person_id(M)');		/* Specifies "limb.person_id" FK */
ModelRelation::define('Category(1):Product(M)', 'nocascade');	/* Prevents cascading delete */
ModelRelation::define('Category(1):Category(M)');	/* A recursive relationship. See related section below. */

Read/write examples:

$house = Model::create('House');
$window = Model::create('Window');
$house->addRelatedModel($window);

/* For a recursive relationship */
$catA = Model::create('Category');
$catB = Model::create('Category');
$catA->addRelatedModel($catB);	/* $catB becomes a child of $catA */
$catB->addRelatedModel($catA, ModelRelation::REF_CHILD);	/* Same as above, but indicating "Set $catA as $catB's parent" */

M:1

Definition examples:

ModelRelation::define('Leaf(M):Tree(1)');

Read/write examples:

$leaf = Model::create('Leaf');
$tree = Model::create('Tree');
$leaf->addRelatedModel($tree);

M:M

Many-to-many relationships are actually defined internally within Buan as 1:M:1 relationships. The "M" in this relationship is the linking Model that joins the two "1" Models together.

Furthermore, this relationship is further broken down into two sub-relationships; a 1:M and a M:1.

Definition examples:

ModelRelation::define('Book(M):Author(M)');			/* Presumes linking model "BookAuthor" with FKs "book_id" and "author_id" */
ModelRelation::define('Friend(1):Mates.left_id.right_id(M):Friend(1)');		/* Recursive relationship, "Mates" is linking Model */

Read/write examples:

Recursive relationships

As shown above, Buan handles recursive relationships by means of relationship references.

In a typical 1:M relationship you have a parent (the "1") and a child (the "M").