Thymeleaf th：field不绑定输入文本的值

Question

这是我的控制器：

@GetMapping("/food/buy/{fid}")
public String buyFood(HttpServletRequest request, @PathVariable("fid") Long fid, Model model) {
    Food food = consumerService.getFood(fid);
    System.out.println("foodid = " + food.getId());
    model.addAttribute("food", food);
    model.addAttribute("order", new OrderVO());
    return "user/direct/f_order";
}

我的观点是：

<form th:action="@{/user/buy/direct/food}" method="post" th:object="${order}">
    <table border="1px">
        <tr th:hidden="true">
            <td><input type="text" th:value="${food.id}" th:field="*{fid}" th:readonly="true"></td>
        </tr>
    </table>
</form>

和VO类：

public class OrderVO {
    private Long fid, address;

    private Integer amount;

    @DateTimeFormat(pattern = "HH:mm")
    private Date deliverTime;
}

<tr>
    <td>UserName</td>
    <td><input type="text" th:value="*{userName}" th:field="*{userName}"></td>
</tr>