Honor primary_key option in $belongs_to.

Fixes #364.

Author: xak2000

lib/Relationship.php

@@ -685,6 +685,9 @@ public function load(Model $model)
  */
 class BelongsTo extends AbstractRelationship
 {
+
+	static protected $valid_association_options = array('primary_key');
+
 	public function __construct($options=array())
 	{
 		parent::__construct($options);
@@ -695,6 +698,9 @@ public function __construct($options=array())
 		//infer from class_name
 		if (!$this->foreign_key)
 			$this->foreign_key = array(Inflector::instance()->keyify($this->class_name));
+
+		if (!isset($this->primary_key) && isset($this->options['primary_key']))
+			$this->primary_key = is_array($this->options['primary_key']) ? $this->options['primary_key'] : array($this->options['primary_key']);
 	}
 
 	public function __get($name)

test/RelationshipTest.php

@@ -165,6 +165,19 @@ public function test_belongs_to_with_explicit_foreign_key()
 		Book::$belongs_to = $old;
 	}
 
+	public function test_belongs_to_with_explicit_primary_key()
+	{
+		$old = Book::$belongs_to;
+		Book::$belongs_to = array(array('explicit_author', 'class_name' => 'Author', 'primary_key' => 'parent_author_id'));
+
+		$book = Book::find(1);
+		$this->assert_equals(1, $book->author_id);
+		$this->assert_equals(1, $book->explicit_author->parent_author_id);
+		$this->assert_equals(3, $book->explicit_author->author_id);
+
+		Book::$belongs_to = $old;
+	}
+
 	public function test_belongs_to_with_select()
 	{
 		Event::$belongs_to[0]['select'] = 'id, city';