ASP.NET Core中处理可选HTML表单输入及设置默认值

[HttpPost("API/SetCartIdentity")]
public async Task<IActionResult> SetCartIdentityAsync(
    [FromForm(Name = "AddressLine1")] string addressLine1,
    [FromForm(Name = "AddressLine2")] string addressLine2,
    [FromForm(Name = "AddressLine3")] string addressLine3,
    [FromForm(Name = "AddressLine4")] string addressLine4,
    [FromForm(Name = "AddressLine5")] string addressLine5 = "default value") // 这里的默认值可能不会生效
{
    // ... 业务逻辑
    return RedirectToActionPermanent("Checkout", "Cart");
}

using System.ComponentModel.DataAnnotations;

namespace YourApplication.Models
{
    public class AddressInputModel
    {
        // 必填字段，使用 [Required] 属性进行标记
        [Required(ErrorMessage = "地址行1是必填项。")]
        public string AddressLine1 { get; set; }

        [Required(ErrorMessage = "地址行2是必填项。")]
        public string AddressLine2 { get; set; }

        // 可选字段，不使用 [Required] 属性
        public string AddressLine3 { get; set; }

        public string AddressLine4 { get; set; }

        // 可选字段，并设置默认值
        public string AddressLine5 { get; set; } = "默认值";
    }
}

using Microsoft.AspNetCore.Mvc;
using System.Threading.Tasks;
using YourApplication.Models; // 确保引用了模型所在的命名空间

[ApiController] // 如果是API控制器，通常会使用此属性
[Route("api")] // 定义路由前缀
public class CartController : ControllerBase
{
    [HttpPost("SetCartIdentity")]
    public async Task<IActionResult> SetCartIdentityAsync(AddressInputModel model)
    {
        // 在此处，model 对象将包含表单提交的数据
        // 如果 AddressLine1 或 AddressLine2 未提交或为空，ModelState.IsValid 将为 false
        // 如果 AddressLine3 或 AddressLine4 未提交，它们将为 null
        // 如果 AddressLine5 未提交，它将是 "默认值"

        // 强烈建议进行模型验证
        if (!ModelState.IsValid)
        {
            // 如果模型验证失败，返回错误信息
            // 可以通过 ModelState 获取详细的验证错误
            return BadRequest(ModelState);
        }

        // 业务逻辑处理，例如保存地址信息到数据库
        // string address1 = model.AddressLine1;
        // string address5 = model.AddressLine5; // 此时 address5 可能是用户提交的值，也可能是 "默认值"

        return RedirectToActionPermanent("Checkout", "Cart");
    }
}

<form asp-action="SetCartIdentity" asp-controller="Cart" method="post">
    <table>
        <tr>
            <td>地址行1 (必填):</td>
            <td><input type="text" id="AddressLine1" name="AddressLine1" class="txt-antan address-line" /></td>
        </tr>
        <tr>
            <td>地址行2 (必填):</td>
            <td><input type="text" id="AddressLine2" name="AddressLine2" class="txt-antan address-line" /></td>
        </tr>
        <tr>
            <td>地址行3 (可选):</td>
            <td><input type="text" id="AddressLine3" name="AddressLine3" class="txt-antan address-line" /></td>
        </tr>
        <tr>
            <td>地址行4 (可选):</td>
            <td><input type="text" id="AddressLine4" name="AddressLine4" class="txt-antan address-line" /></td>
        </tr>
        <tr>
            <td>地址行5 (可选, 有默认值):</td>
            <td><input type="text" id="AddressLine5" name="AddressLine5" class="txt-antan address-line" placeholder="例如：门牌号" /></td>
        </tr>
        <tr>
            <td colspan="2"><button type="submit">提交地址信息</button></td>
        </tr>
    </table>
</form>