好，我已经按照我想要的方式工作了.我不得不修改我为mvc网络api找到的一些类似代码，但使其变得更加简单.如下创建您的自定义模型联编程序并将其添加到globalconfiguration.希望这对其他人有帮助.

Ok, I got this working the way I want. I had to adapt some similar code I found for an mvc web api, but made it a lot simpler. Create your custom model binder as below and add it to the globalconfiguration. Hope this helps someone else.

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        // Web API configuration and services
        GlobalConfiguration.Configuration.BindParameter(typeof(string), new EmptyStringModelBinder());

        // Web API routes
        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{action}"
        );
    }
}

public class EmptyStringModelBinder : System.Web.Http.ModelBinding.IModelBinder
{
    public bool BindModel(HttpActionContext actionContext, System.Web.Http.ModelBinding.ModelBindingContext bindingContext)
    {
        string val = bindingContext.ValueProvider.GetValue(bindingContext.ModelName).AttemptedValue;
        bindingContext.Model = val;

        return true;
    }
}