Add assoc method into SqlResultCollection

Model/SqlResultCollection.php

@@ -37,4 +37,9 @@ class SqlResultCollection extends \ArrayIterator implements iSqlResultItems
     {
         return $this->offsetGet(0);
     }
+
+	public function assoc($field, $assoc_as_array = false) {
+		$sql_result_provider = new SqlResultProvider($this->items);
+		return $sql_result_provider->assoc($field, $assoc_as_array);
+	}
 }