使用 ASP.NET Web API。如果参数为空，有没有办法自动返回状态码 400？我发现了这个问题，但这是一个适用于所有方法的全局解决方案，我想在每个方法每个参数的基础上执行此操作。
因此，例如，这就是我目前正在做的事情：
public HttpResponseMessage SomeMethod(SomeNullableParameter parameter)
{
if (parameter == null)
throw new HttpResponseException(HttpStatusCode.BadRequest);
// Otherwise do more stuff.
}
我真的很想做这样的事情（注意 required 属性）：
public HttpResponseMessage SomeMethod([Required] SomeNullableParameter parameter)
{
// Do stuff.
}
我最终使用的方法是创建一个我在全球注册的自定义过滤器。过滤器检查所有请求参数RequiredAttribute。如果找到该属性，则检查参数是否随请求一起传递（非空），如果为空，则返回状态代码 400。我还在过滤器中添加了一个缓存来存储每个请求所需的参数，以避免对未来调用的反射命中。我惊喜地发现这也适用于值类型，因为操作上下文将参数存储为对象。
编辑 - 根据 tecfield 的评论更新解决方案
public class RequiredParametersFilter : ActionFilterAttribute
{
// Cache used to store the required parameters for each request based on the
// request's http method and local path.
private readonly ConcurrentDictionary<Tuple<HttpMethod, string>, List<string>> _Cache =
new ConcurrentDictionary<Tuple<HttpMethod, string>, List<string>>();
public override void OnActionExecuting(HttpActionContext actionContext)
{
// Get the request's required parameters.
List<string> requiredParameters = this.GetRequiredParameters(actionContext);
// If the required parameters are valid then continue with the request.
// Otherwise, return status code 400.
if(this.ValidateParameters(actionContext, requiredParameters))
{
base.OnActionExecuting(actionContext);
}
else
{
throw new HttpResponseException(HttpStatusCode.BadRequest);
}
}
private bool ValidateParameters(HttpActionContext actionContext, List<string> requiredParameters)
{
// If the list of required parameters is null or containst no parameters
// then there is nothing to validate.
// Return true.
if (requiredParameters == null || requiredParameters.Count == 0)
{
return true;
}
// Attempt to find at least one required parameter that is null.
bool hasNullParameter =
actionContext
.ActionArguments
.Any(a => requiredParameters.Contains(a.Key) && a.Value == null);
// If a null required paramter was found then return false.
// Otherwise, return true.
return !hasNullParameter;
}
private List<string> GetRequiredParameters(HttpActionContext actionContext)
{
// Instantiate a list of strings to store the required parameters.
List<string> result = null;
// Instantiate a tuple using the request's http method and the local path.
// This will be used to add/lookup the required parameters in the cache.
Tuple<HttpMethod, string> request =
new Tuple<HttpMethod, string>(
actionContext.Request.Method,
actionContext.Request.RequestUri.LocalPath);
// Attempt to find the required parameters in the cache.
if (!this._Cache.TryGetValue(request, out result))
{
// If the required parameters were not found in the cache then get all
// parameters decorated with the 'RequiredAttribute' from the action context.
result =
actionContext
.ActionDescriptor
.GetParameters()
.Where(p => p.GetCustomAttributes<RequiredAttribute>().Any())
.Select(p => p.ParameterName)
.ToList();
// Add the required parameters to the cache.
this._Cache.TryAdd(request, result);
}
// Return the required parameters.
return result;
}
}
在模型中设置[Required]一个属性，然后检查ModelState它是否存在IsValid。
这将允许同时测试所有必需的属性。
请参阅“Under-Posting”部分@WebAPI 中的模型验证
我们可以使用BindRequired来自Microsoft.AspNetCore.Mvc.ModelBinding命名空间的 .
public async Task<ActionResult<IEnumerable<Numbers>>> GetAll([BindRequired, FromQuery]string[] numbers)
{
var result = await _service.GetAllDetails(numbers);
return Ok(result);
}
之后，您的招摇将如下所示。
asp.net core的解决方案...
[AttributeUsage(AttributeTargets.Method)]
public sealed class CheckRequiredModelAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext context)
{
var requiredParameters = context.ActionDescriptor.Parameters.Where(
p => ((ControllerParameterDescriptor)p).ParameterInfo.GetCustomAttribute<RequiredModelAttribute>() != null).Select(p => p.Name);
foreach (var argument in context.ActionArguments.Where(a => requiredParameters.Contains(a.Key, StringComparer.Ordinal)))
{
if (argument.Value == null)
{
context.ModelState.AddModelError(argument.Key, $"The argument '{argument.Key}' cannot be null.");
}
}
if (!context.ModelState.IsValid)
{
var errors = context.ModelState.Values.SelectMany(v => v.Errors).Select(e => e.ErrorMessage);
context.Result = new BadRequestObjectResult(errors);
return;
}
base.OnActionExecuting(context);
}
}
[AttributeUsage(AttributeTargets.Parameter)]
public sealed class RequiredModelAttribute : Attribute
{
}
services.AddMvc(options =>
{
options.Filters.Add(typeof(CheckRequiredModelAttribute));
});
public async Task<IActionResult> CreateAsync([FromBody][RequiredModel]RequestModel request, CancellationToken cancellationToken)
{
//...
}
公认的解决方案会自行报告任何错误。MVC5 更合适的方法是让控制器处理（通过模型验证）任何错误的报告，也就是这样：
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Web.Http.Controllers;
using System.Web.Http.Filters;
using System.Web.Http.ModelBinding;
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true)]
public sealed class ValidateParametersAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(HttpActionContext context)
{
var descriptor = context.ActionDescriptor;
if (descriptor != null)
{
var modelState = context.ModelState;
foreach (var parameterDescriptor in descriptor.GetParameters())
{
EvaluateValidationAttributes(
suppliedValue: context.ActionArguments[parameterDescriptor.ParameterName],
modelState: modelState,
parameterDescriptor: parameterDescriptor
);
}
}
base.OnActionExecuting(context);
}
static private void EvaluateValidationAttributes(HttpParameterDescriptor parameterDescriptor, object suppliedValue, ModelStateDictionary modelState)
{
var parameterName = parameterDescriptor.ParameterName;
parameterDescriptor
.GetCustomAttributes<object>()
.OfType<ValidationAttribute>()
.Where(x => !x.IsValid(suppliedValue))
.ForEach(x => modelState.AddModelError(parameterName, x.FormatErrorMessage(parameterName)));
}
}
然后，您可以通过 WebApiConfig.cs 将其普遍插入：
config.Filters.Add(new ValidateParametersAttribute());