你可以抛出一个HttpResponseException

HttpResponseMessage response = 
    this.Request.CreateErrorResponse(HttpStatusCode.BadRequest, "your message");
throw new HttpResponseException(response);

你可以抛出一个HttpResponseException

HttpResponseMessage response = 
    this.Request.CreateErrorResponse(HttpStatusCode.BadRequest, "your message");
throw new HttpResponseException(response);

欢迎来到2022年!现在我们在. net中有了其他的答案(因为ASP。NET Core 2.1)。请看这篇文章:在ASP中使用ProblemDetails类。NET Core Web API，作者在其中解释了以下最佳实践:

如何实现标准IETF RFC 7807，它将“问题细节”定义为一种在HTTP响应中携带机器可读的错误细节的方法，以避免为HTTP api定义新的错误响应格式。 模型验证如何使用ProblemDetails类来填充验证错误列表——这是对一般规则问题的直接回答，即在出现第一个错误后是否中断处理。

作为一个挑逗，如果我们使用ProductDetails和多个错误，JSON输出是这样的:

试试这个

[HttpPost]
public async Task<ActionResult<User>> PostUser(int UserTypeId, User user)
{
  if (somethingFails)
  {
    // Return the error message like this.
    return new BadRequestObjectResult(new
    {
      message = "Something is not working here"
    });
  }

  return ok();
}

如果您正在使用ASP。NET Web API 2，最简单的方法是使用ApiController Short-Method。这将导致一个BadRequestResult。

return BadRequest("message");

基于Manish Jain的回答(这意味着Web API 2简化了事情):

1)使用验证结构来响应尽可能多的验证错误。这些结构还可以用于响应来自表单的请求。

public class FieldError
{
    public String FieldName { get; set; }
    public String FieldMessage { get; set; }
}

// a result will be able to inform API client about some general error/information and details information (related to invalid parameter values etc.)
public class ValidationResult<T>
{
    public bool IsError { get; set; }

    /// <summary>
    /// validation message. It is used as a success message if IsError is false, otherwise it is an error message
    /// </summary>
    public string Message { get; set; } = string.Empty;

    public List<FieldError> FieldErrors { get; set; } = new List<FieldError>();

    public T Payload { get; set; }

    public void AddFieldError(string fieldName, string fieldMessage)
    {
        if (string.IsNullOrWhiteSpace(fieldName))
            throw new ArgumentException("Empty field name");

        if (string.IsNullOrWhiteSpace(fieldMessage))
            throw new ArgumentException("Empty field message");

        // appending error to existing one, if field already contains a message
        var existingFieldError = FieldErrors.FirstOrDefault(e => e.FieldName.Equals(fieldName));
        if (existingFieldError == null)
            FieldErrors.Add(new FieldError {FieldName = fieldName, FieldMessage = fieldMessage});
        else
            existingFieldError.FieldMessage = $"{existingFieldError.FieldMessage}. {fieldMessage}";

        IsError = true;
    }

    public void AddEmptyFieldError(string fieldName, string contextInfo = null)
    {
        AddFieldError(fieldName, $"No value provided for field. Context info: {contextInfo}");
    }
}

public class ValidationResult : ValidationResult<object>
{

}

2)不管操作是否成功，服务层都会返回ValidationResults。例句:

    public ValidationResult DoSomeAction(RequestFilters filters)
    {
        var ret = new ValidationResult();

        if (filters.SomeProp1 == null) ret.AddEmptyFieldError(nameof(filters.SomeProp1));
        if (filters.SomeOtherProp2 == null) ret.AddFieldError(nameof(filters.SomeOtherProp2 ), $"Failed to parse {filters.SomeOtherProp2} into integer list");

        if (filters.MinProp == null) ret.AddEmptyFieldError(nameof(filters.MinProp));
        if (filters.MaxProp == null) ret.AddEmptyFieldError(nameof(filters.MaxProp));


        // validation affecting multiple input parameters
        if (filters.MinProp > filters.MaxProp)
        {
            ret.AddFieldError(nameof(filters.MinProp, "Min prop cannot be greater than max prop"));
            ret.AddFieldError(nameof(filters.MaxProp, "Check"));
        }

        // also specify a global error message, if we have at least one error
        if (ret.IsError)
        {
            ret.Message = "Failed to perform DoSomeAction";
            return ret;
        }

        ret.Message = "Successfully performed DoSomeAction";
        return ret;
    }

3) API Controller将根据服务功能结果构建响应

一种选择是将几乎所有参数都设置为可选，并执行自定义验证，从而返回更有意义的响应。另外，我注意不允许任何异常超出服务边界。

    [Route("DoSomeAction")]
    [HttpPost]
    public HttpResponseMessage DoSomeAction(int? someProp1 = null, string someOtherProp2 = null, int? minProp = null, int? maxProp = null)
    {
        try
        {
            var filters = new RequestFilters 
            {
                SomeProp1 = someProp1 ,
                SomeOtherProp2 = someOtherProp2.TrySplitIntegerList() ,
                MinProp = minProp, 
                MaxProp = maxProp
            };

            var result = theService.DoSomeAction(filters);
            return !result.IsError ? Request.CreateResponse(HttpStatusCode.OK, result) : Request.CreateResponse(HttpStatusCode.BadRequest, result);
        }
        catch (Exception exc)
        {
            Logger.Log(LogLevel.Error, exc, "Failed to DoSomeAction");
            return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, new HttpError("Failed to DoSomeAction - internal error"));
        }
    }