@Override
  public String toString() {
    String s = "";

    for (int i = 0; i < items.size(); i++) {
      SearchConditionItem item = items.get(i);
      if (item instanceof SearchConditionGroupItem) {
        s += "(" + item.toString() + ")";
      } else {
        s += item.toString();
      }
      if (i != items.size()) {
        s += " " + this.getRelation() + " ";
      }
    }

    return s;
  }