在阅读这篇文章的时候，我想你已经看完第一篇文章啦·也有可能跟我一样，现在正在使用它Asp.net WebAPI为我们干活儿。可能是服务分页查询接口，也可能是其它操作，遇到了一些小问题。有问题，那咱就来解决问题吧！（码农万岁，万岁，万万岁！）

扯两句，Asp.net MVC WebAPI，是建立在Asp.net MVC基础上的。所有的请求处理，都遵循MVC的路由规则，对于请求的拦截与处理，都可以通过自定义继承自

System.Web.Http.Filters.ActionFilterAttribute

的任意标记类，然后重写里面的4个方法OnActionExecuted,OnActionExecutedAsync,OnActionExecuting

OnActionExecutingAsync 来实现对请求的拦截，过滤等等。最后通过Action标记，或者通 Global.asax 中进行全局注册。就可以实现MVC的请求拦截与自定义的逻辑管理了。

看看它的庐山真面目。定义如下：

public abstract class ActionFilterAttribute : FilterAttribute, IActionFilter, IFilter

可以看到，它是一个抽象类，继承自FilterAttribute，同时实现了IActionFilter,IFilter两个接口。（不再往里面扒了，有兴趣你可以自己瞧瞧，也可以整本ASP.NET MVC的技术书看看。）

下面是部分核心代码的实现（参考：System.Web.OData项目源码的EnableQueryAttribute对象定义）

    /// <summary>/// 标记Action返回结果为分页数据对象。/// Action本身必须返回IQueryable&lt;T>/// -------------------------------------/// add by hotboy 2015-5-14 11:32:27/// </summary>[AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]public class ODataPagedAttribute : System.Web.Http.Filters.ActionFilterAttribute{private const char CommaSeparator = ',';private const string PageSizeKey = "$pagesize";private const int DefaultPageSize = 20;// validation settingsprivate ODataValidationSettings _validationSettings;private string _allowedOrderByProperties;// query settingsprivate ODataQuerySettings _querySettings;/// <summary>/// Enables a controller action to support OData query parameters./// </summary>public ODataPagedAttribute(){_validationSettings = new ODataValidationSettings();_querySettings = new ODataQuerySettings();}//... more than code here ....//    }//// IQeruyable静态方法，参考：System.Web.OData.Extension的QueryableExtensions// 用于查询分页数据以及数据记录总数。public class QueryableExtensions{private static MethodInfo _limitResultsGenericMethod = typeof(QueryableExtensions).GetMethod("LimitResults");internal static IQueryable LimitResults(IQueryable queryable, int limit, out bool resultsLimited, out int total){MethodInfo genericMethod = _limitResultsGenericMethod.MakeGenericMethod(queryable.ElementType);object[] args = new object[] { queryable, limit, null, null };IQueryable results = genericMethod.Invoke(null, args) as IQueryable;resultsLimited = (bool)args[2];total = (int)args[3];return results;}/// <summary>/// Limits the query results to a maximum number of results./// </summary>/// <typeparam name="T">The entity CLR type</typeparam>/// <param name="queryable">The queryable to limit.</param>/// <param name="limit">The query result limit.</param>/// <param name="resultsLimited"><c>true</c> if the query results were limited; <c>false</c> otherwise</param>/// <returns>The limited query results.</returns>        public static IQueryable<T> LimitResults<T>(IQueryable<T> queryable, int limit, out bool resultsLimited, out int total){total = queryable.Count();TruncatedCollection<T> truncatedCollection = new TruncatedCollection<T>(queryable, limit);resultsLimited = truncatedCollection.IsTruncated;return truncatedCollection.AsQueryable();}}// Type管理辅助Helperinternal static class TypeHelper {internal static Type GetImplementedIEnumerableType(Type type){// get inner type from Task<T>if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Task<>)){type = type.GetGenericArguments().First();}if (type.IsGenericType && type.IsInterface &&(type.GetGenericTypeDefinition() == typeof(IEnumerable<>) ||type.GetGenericTypeDefinition() == typeof(IQueryable<>))){// special case the IEnumerable<T>return GetInnerGenericType(type);}else{// for the rest of interfaces and strongly Type collectionsType[] interfaces = type.GetInterfaces();foreach (Type interfaceType in interfaces){if (interfaceType.IsGenericType &&(interfaceType.GetGenericTypeDefinition() == typeof(IEnumerable<>) ||interfaceType.GetGenericTypeDefinition() == typeof(IQueryable<>))){// special case the IEnumerable<T>return GetInnerGenericType(interfaceType);}}}return null;}private static Type GetInnerGenericType(Type interfaceType){// Getting the type T definition if the returning type implements IEnumerable<T>Type[] parameterTypes = interfaceType.GetGenericArguments();if (parameterTypes.Length == 1){return parameterTypes[0];}return null;}}

下一篇文章，将介绍怎么样使用它，以及项目中需要注意事项与项目源代码下载地址。