Allow associations to be iterated

Added an iterator to the class so that associations can be looped through

src/ORM/AssociationCollection.php

@@ -14,19 +14,21 @@
  */
 namespace Cake\ORM;
 
+use ArrayIterator;
 use Cake\ORM\Association;
 use Cake\ORM\AssociationsNormalizerTrait;
 use Cake\ORM\Entity;
 use Cake\ORM\Table;
 use InvalidArgumentException;
+use IteratorAggregate;
 
 /**
  * A container/collection for association classes.
  *
  * Contains methods for managing associations, and
  * ordering operations around saving and deleting.
  */
-class AssociationCollection
+class AssociationCollection implements IteratorAggregate
 {
 
     use AssociationsNormalizerTrait;
@@ -292,4 +294,14 @@ public function normalizeKeys($keys)
 
         return $this->_normalizeAssociations($keys);
     }
+
+    /**
+     * Allow looping through the associations
+     * 
+     * @return \Cake\ORM\Association
+     */
+    public function getIterator()
+    {
+        return new ArrayIterator($this->_items);
+    }
 }