@Override
  public String toString() {
    StringBuilder sb = new StringBuilder("Book(");
    boolean first = true;

    sb.append("id:");
    sb.append(this.id);
    first = false;
    if (!first) sb.append(", ");
    sb.append("name:");
    if (this.name == null) {
      sb.append("null");
    } else {
      sb.append(this.name);
    }
    first = false;
    if (!first) sb.append(", ");
    sb.append("price:");
    sb.append(this.price);
    first = false;
    sb.append(")");
    return sb.toString();
  }