Dont set primaryKey to MongoId

src/Jenssegers/Mongodb/Relations/EmbedsMany.php

@@ -163,9 +163,9 @@ class EmbedsMany extends Relation {
     protected function performInsert(Model $model)
     {
         // Create a new key.
-        if (!$model->getKey())
+        if (!isset($model['_id']))
         {
-            $model->setAttribute($model->getKeyName(), new MongoId);
+            $model->setAttribute('_id', new MongoId);
         }
 
         // Set timestamps.

tests/RelationsTest.php

@@ -292,6 +292,7 @@ class RelationsTest extends PHPUnit_Framework_TestCase {
         $this->assertEquals(array('London'), $user->addresses->lists('city'));
         $this->assertInstanceOf('DateTime', $address->created_at);
         $this->assertInstanceOf('DateTime', $address->updated_at);
+        $this->assertNotNull($address->_id);
 
         $address = $user->addresses()->save(new Address(array('city' => 'Paris')));