在 Web API 中返回自定义错误对象

Question

我正在使用 MVC 4 Web API 框架开发一个 Web API。如果有异常，我目前正在抛出一个新的 HttpResponseException。即：

if (!Int32.TryParse(id, out userId))
    throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.BadRequest, "Invalid id")); 

这会向客户端返回一个简单的对象 {"message":"Invalid id"}

我想通过返回更详细的对象来进一步控制对异常的响应。像

{
 "status":-1,
 "substatus":3,
 "message":"Could not find user"
 }

我该怎么做呢？序列化我的错误对象并将其设置在响应消息中的最佳方法是什么？

我也稍微研究了ModelStateDictionary，并提出了这个“hack”，但它仍然不是一个干净的输出：

var msd = new ModelStateDictionary();
msd.AddModelError("status", "-1");
msd.AddModelError("substatus", "3");
msd.AddModelError("message", "invalid stuff");
throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.BadRequest, msd));

编辑
看起来像自定义HttpError 是我需要的。这似乎可以解决问题，现在让它可以从我的业务层扩展......

var error = new HttpError("invalid stuff") {{"status", -1}, {"substatus", 3}};
throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.BadRequest, error));

Answer 1

看看下面的文章。它将帮助您控制您的 Web api 异常和错误消息：Web Api, HttpError, and the Behavior of Exceptions

Answer 2

这些答案比他们需要的要复杂得多。

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        config.Filters.Add(new HandleApiExceptionAttribute());
        // ...
    }
}

public class HandleApiExceptionAttribute : ExceptionFilterAttribute
{
    public override void OnException(HttpActionExecutedContext context)
    {
        var request = context.ActionContext.Request;

        var response = new
        {
             //Properties go here...
        };

        context.Response = request.CreateResponse(HttpStatusCode.BadRequest, response);
    }
}

这就是你所需要的。它也很容易进行单元测试：

[Test]
public async void OnException_ShouldBuildProperErrorResponse()
{
    var expected = new 
    {
         //Properties go here...
    };

    //Setup
    var target = new HandleApiExceptionAttribute()

    var contextMock = BuildContextMock();

    //Act
    target.OnException(contextMock);

    dynamic actual = await contextMock.Response.Content.ReadAsAsync<ExpandoObject>();

    Assert.AreEqual(expected.Aproperty, actual.Aproperty);
}

private HttpActionExecutedContext BuildContextMock()
{
    var requestMock = new HttpRequestMessage();
    requestMock.Properties.Add(HttpPropertyKeys.HttpConfigurationKey, new HttpConfiguration());

    return new HttpActionExecutedContext()
    {
        ActionContext = new HttpActionContext
        {
            ControllerContext = new HttpControllerContext
            {
                Request = requestMock
            }

        },
        Exception = new Exception()
    };
}

Answer 3

我认为这样可以解决问题：

为业务层创建自定义异常类：

 public class MyException: Exception
 {
    public ResponseStatus Status { get; private set; }
    public ResponseSubStatus SubStatus { get; private set; }
    public new string Message { get; private set; }

    public MyException()
    {}

    public MyException(ResponseStatus status, ResponseSubStatus subStatus, string message)
    {
        Status = status;
        SubStatus = subStatus;
        Message = message;
    }
 }

创建一个静态方法以从MyException 的实例生成HttpError。我在这里使用反射，所以我可以将属性添加到MyException，并且总是在不更新Create的情况下返回它们：

    public static HttpError Create<T>(MyException exception) where T:Exception
    {
        var properties = exception.GetType().GetProperties(BindingFlags.Instance 
                                                         | BindingFlags.Public 
                                                         | BindingFlags.DeclaredOnly);
        var error = new HttpError();
        foreach (var propertyInfo in properties)
        {
            error.Add(propertyInfo.Name, propertyInfo.GetValue(exception, null));
        }
        return error;
    }

我目前有一个通用异常处理程序的自定义属性。所有MyException 类型的异常都将在此处处理：

public class ExceptionHandlingAttribute : ExceptionFilterAttribute
{
    public override void OnException(HttpActionExecutedContext context)
    {
        var statusCode = HttpStatusCode.InternalServerError;

        if (context.Exception is MyException)
        {
            statusCode = HttpStatusCode.BadRequest;
            throw new HttpResponseException(context.Request.CreateErrorResponse(statusCode, HttpErrorHelper.Create(context.Exception)));
        }

        if (context.Exception is AuthenticationException)
            statusCode = HttpStatusCode.Forbidden;

        throw new HttpResponseException(context.Request.CreateErrorResponse(statusCode, context.Exception.Message));
    }
}

当我发现这个计划中的漏洞时，我会多尝试一下并更新。