Web Api必需参数 [英] Web Api Required Parameter

问题描述

使用ASP.NET Web API.如果参数为空，是否可以自动返回状态代码400?我发现了这个问题但这是适用于所有方法的全局解决方案，我想在每个方法的每个参数的基础上执行此操作.

Using ASP.NET Web API. Is there a way to automatically return a status code 400 if a parameter is null? I found this question but that is a global solution that is applied to all methods, I want to do this on a per method per parameter basis.

例如，这就是我目前正在做的事情:

So, for example, this is what I am currently doing:

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(注意必填属性):

I would really just like to do something like this (notice the required attribute):

public HttpResponseMessage SomeMethod([Required] SomeNullableParameter parameter)
{
    // Do stuff.
}

推荐答案

我最终使用的方法是创建一个在全球注册的自定义过滤器.筛选器检查RequiredAttribute的所有请求参数.如果找到了该属性，则它将检查参数是否随请求一起传递(不为null)，如果该参数为null，则返回状态码400.我还向过滤器添加了一个缓存，以存储每个请求所需的参数，以避免在以后的调用中出现反射.由于操作上下文将参数存储为对象，因此我很惊讶地发现它也适用于值类型.

The approach I ended up using was to create a custom filter that I registered globally. The filter checks all request parameters for the RequiredAttribute. If the attribute is found then it checks if the parameter was passed with the request (not null) and returns status code 400 if it was null. I also added a cache to the filter to store the required parameters for each request to avoid the reflection hit on future calls. I was pleasantly surprised to find that this works for value types as well since the action context stores the parameters as objects.

编辑-根据tecfield的评论更新了解决方案

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;
    }

}

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