public function getRoleAssigments($roleName) {
        $query = (new Query)->from($this->assignmentTable)
            ->where(['item_name' => $roleName]);

        $assignments = [];
        foreach ($query->all($this->db) as $row) {
            $assignments[$row['user_id']] = new Assignment([
                'userId' => $row['user_id'],
                'roleName' => $row['item_name'],
                'createdAt' => $row['created_at'],
            ]);
        }

        return $assignments;
    }