ASP.NET - GET 请求上的 API 400 错误

Question

我有这个控制器：

namespace Cantrel.Application.CantrelSearchApi.Controllers
{
    [Route("api/[controller]")]
    [Authorize]
    public class MonitorsController : Controller
    {
        private readonly IMonitoringApiService monitoringService;
        private readonly IClientsApiService clientsService;
        private readonly ILogger<MonitorsController> logger;

        public MonitorsController(IMonitoringApiService monitoringService,
            IClientsApiService clientsService,
            ILogger<MonitorsController> logger)
        {
            this.monitoringService = monitoringService;
            this.clientsService = clientsService;
            this.logger = logger;
        }

  [HttpGet("{id}")]
    public async Task<IActionResult> Get(string id)
    {
        if (string.IsNullOrEmpty(null))
        {
            return BadRequest("No id was provided. Please provide a valid monitor id or subject id.");
        }

        try
        {
            MonitorDto monitor;

            if (Guid.TryParse(id, out Guid monitorId))
            {
                monitor = await GetByMonitorId(monitorId);
            }
            else
            {
                monitor = await GetBySubjectId(id);
            }

            if (monitor == null)
            {
                return NotFound();
            }

            return Json(monitor);
        }
        catch (Exception ex)
        {
            logger.LogError($"[{Request.Path.Value}]: {ex.ToString()}");
            return new StatusCodeResult(500);
        }
    }

我在 Postman 中进行以下调用：

GET: {{api}}/Monitors/ABCDEFGH-1234-4567-8901-ABCDEFGHIJKL

我收到了400 Bad Request 错误消息No id was provided. Please provide a valid monitor id or subject id，而不是预期的信息返回。

我不确定我是否理解这是怎么发生的。该字符串显然既不是 NULL 也不是空的。

如果我应该提供任何其他类的代码来帮助诊断，请告诉我。

Answer 1

这总是正确的：

        if (string.IsNullOrEmpty(null)) //always true!
        {
            return BadRequest("No id was provided. Please provide a valid monitor id or subject id.");
        }

因此，您将始终收到 BadRequest 响应。您需要将其更改为：

if (string.IsNullOrEmpty(id))