带有 WCF 的 ASP.NET MVC，缓存通知问题

Question

我有一个为我的 asp.net 应用程序提供数据的 WCF。我想在应用程序中缓存这些数据，但我不知道是否有现成的机制来制作依赖通知。

具体来说，我需要这样的东西：

• WCF 返回数据
• 客户端获取此数据并放入缓存中
• 现在客户端从其缓存中返回数据
• WCF 中的数据突然发生变化
• 客户端收到通知（？）并再次用新数据填充缓存

如果没有现成的机制，你会如何解决？

Answer 1

我认为你需要的是一个自定义的 CacheDependency 对象，它每 n 秒调用一次 WCF 服务（其中 n 是可接受的延迟量）并与以前的结果，看看数据是否更新。然后，您的自定义依赖项可以调用其'NotifyDependencyChanged 方法，该方法告诉 ASP.NET 基础数据已更改并且缓存的对象已过时。有一个关于创建自定义 CacheDependency 对象here 的教程。

我认为您的自定义 CacheDependency 看起来像这样（未经测试的代码）：

/// <summary>
/// DTO for encapsulating stuff needed to create the dependency
/// </summary>
public class WebServiceCacheDependencySetup
{
    public object serviceClient { get; set; }
    public string clientMethod { get; set; }
    public int pollInterval { get; set; }
}

/// <summary>
/// Generic web services cache dependency
/// </summary>
public class WebServiceCacheDependency : CacheDependency
{
    private Timer timer;
    private static string previousHash;

    private object client;
    private string clientMethod;

    /// <summary>
    /// Constructor for the cache dependency
    /// </summary>
    /// <param name="setup">Object that specifies how to create dependency and call the dependent web service method</param>
    public WebServiceCacheDependency(WebServiceCacheDependencySetup setup)
    {
        // Create a timer with a specified poll interval
        timer = new Timer(CheckDependencyCallback, this, 0, setup.pollInterval);

        client = setup.serviceClient;
        clientMethod = setup.clientMethod;

        previousHash = string.Empty;
    }

    public void CheckDependencyCallback(object sender)
    {
        // Reflect on the service's proxy to find the method we want to call
        Type clientType = client.GetType();
        MethodInfo method = clientType.GetMethod(clientMethod);

        // Programmatically invoke the method and get the return value
        object returnValue = method.Invoke(client, null);

        // Cast the return to a byte array so we can hash it
        Byte[] returnBytes = (Byte[])returnValue;

        using (SHA512Managed hashAlgorithm = new SHA512Managed())
        {
            // Hash the return value into a string
            Byte[] hashedBytes = hashAlgorithm.ComputeHash(returnBytes);
            string hashedValue = Convert.ToBase64String(hashedBytes);

            // Compare the new hash to the last hash
            if (hashedValue != previousHash)
            {
                // If the hashes don't match then the web service result has changed
                // so invalidate the cached object
                NotifyDependencyChanged(this, EventArgs.Empty);

                // Tear down this instance
                timer.Dispose();
            }
        }

    }

    protected override void DependencyDispose()
    {
        if (timer != null)
        {
            timer.Dispose();
        }
    }
}