避免空模型时，没有数据被张贴在网页API [英] Avoid null model when no data is posted in Web API

问题描述

这个问题是相似，我想实现：

This question is similar to what I want to achieve:

<一个href=\"http://stackoverflow.com/questions/25160345/avoiding-null-model-in-asp-net-web-api-when-no-posted-properties-match-the-model\">Avoiding在ASP.Net的Web API空模型时没有发表任何属性的模型匹配

但它的消失未回答。

我有这需要一个模型，是一个GET路线：

I have a route which takes a model that is a GET:

    [HttpGet, Route("accounts")]
    public AccountListResult Post(AccountListRequest loginRequest)
    {
        return accountService.GetAccounts(loginRequest);
    }

该模型中填充额外的数据，从一个动作过滤器。

The model is populated with additional data from an action filter.

在需要知道这种情况下，所有的用户ID，该行动过滤器添加的基于cookie的/头模型与请求传递。

In this case all that needs to be known is the UserId, which the action filter add's to the model based on cookie/header into passed in with the request.

我想用所有的默认模型中的WebAPI约束力，但我想避免空的对象。

I want to use all the default model binding in WebAPI but I want to avoid null objects.

我不相信模型的结合解决了我的问题。

I don't believe model binding solves my problem.

<一个href=\"http://stackoverflow.com/questions/26527492/how-do-i-replace-the-behaviour-of-web-api-model-binding-so-that-instead-of-null\">How我取代的Web API模型结合，使而不是空的，我收到一个新的实例时没有参数传递的行为

这是接近我想，除了这是乏味的每种类型的事情。

This is closer to what I want to do except its per type which is tedious.

推荐答案

编辑：由于问题是Web API，我张贴也低于网页API的解决方案。

Since the question is for Web API, I am posting the Web API solution also below.

您可以在操作过滤器如下做到这一点。下面code仅如果模型包含默认构造函数。

You can do this as below in an Action Filter. The below code works only if your model contains default constructor.

网络API实现：

public override void OnActionExecuting(HttpActionContext actionContext)
{
     var parameters = actionContext.ActionDescriptor.GetParameters();

     foreach (var parameter in parameters)
     {
         object value = null;

         if (actionContext.ActionArguments.ContainsKey(parameter.ParameterName))
             value = actionContext.ActionArguments[parameter.ParameterName];

         if (value != null)
            continue;

         value = CreateInstance(parameter.ParameterType);
         actionContext.ActionArguments[parameter.ParameterName] = value;
     }

     base.OnActionExecuting(actionContext);
}

protected virtual object CreateInstance(Type type)
{
   // Check for existence of default constructor using reflection if needed
   // and if performance is not a constraint.

   // The below line will fail if the model does not contain a default constructor.
   return Activator.CreateInstance(type);
}

MVC实现：

public override void OnActionExecuting(ActionExecutingContext filterContext)
{
    var parameters = filterContext.ActionDescriptor.GetParameters();

    foreach (var parameter in parameters)
    {
        if (filterContext.ActionParameters.ContainsKey(parameter.ParameterName))
        {
            object value = filterContext.ActionParameters[parameter.ParameterName];

            if (value == null)
            {
                 // The below line will fail if the model does not contain a default constructor.
                 value = Activator.CreateInstance(parameter.ParameterType);                          
                 filterContext.ActionParameters[parameter.ParameterName] = value;
            }
        }                
    }

    base.OnActionExecuting(filterContext);
}

这篇关于避免空模型时，没有数据被张贴在网页API的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！