如何在 C# Core Console 应用程序中使用 MemoryCache？

Question

我想在 .NET Core 2.0 控制台应用程序中使用 Microsoft.Extensions.Caching.Memory.MemoryCache（实际上，在一个用于控制台或 asp.net 应用程序的库中）

我创建了一个测试应用：

using System;

namespace ConsoleTest
{
    class Program
    {
        static void Main(string[] args)
        {
            var cache = new Microsoft.Extensions.Caching.Memory.MemoryCache(new Microsoft.Extensions.Caching.Memory.MemoryCacheOptions());

            int count = cache.Count;
            cache.CreateEntry("item1").Value = 1;
            int count2 = cache.Count;
            cache.TryGetValue("item1", out object item1);
            int count3 = cache.Count;
            cache.TryGetValue("item2", out object item2);
            int count4 = cache.Count;

            Console.WriteLine("Hello World!");
        }
    }
}

很遗憾，这不起作用。这些项目未添加到缓存中，并且无法检索。

我怀疑我需要使用 DependencyInjection，做这样的事情：

using System;
using Microsoft.Extensions.DependencyInjection;

namespace ConsoleTest
{
    class Program
    {
        static void Main(string[] args)
        {
            var provider = new Microsoft.Extensions.DependencyInjection.ServiceCollection()
                .AddMemoryCache()
                .BuildServiceProvider();

            //And now?

            var cache = new Microsoft.Extensions.Caching.Memory.MemoryCache(new Microsoft.Extensions.Caching.Memory.MemoryCacheOptions());

            var xxx = PSP.Helpers.DependencyInjection.ServiceProvider;
            int count = cache.Count;
            cache.CreateEntry("item1").Value = 1;
            int count2 = cache.Count;
            cache.TryGetValue("item1", out object item1);
            int count3 = cache.Count;
            cache.TryGetValue("item2", out object item2);
            int count4 = cache.Count;

            Console.WriteLine("Hello World!");
        }
    }
}

不幸的是，这也不起作用，我怀疑我不应该创建新的内存缓存，而是从服务提供商那里获取它，但一直无法做到。

有什么想法吗？

Answer 1

配置提供程序后，通过GetService 扩展方法检索缓存

var provider = new ServiceCollection()
                       .AddMemoryCache()
                       .BuildServiceProvider();

//And now?
var cache = provider.GetService<IMemoryCache>();

//...other code removed for brevity;

来自 cmets：

不需要使用依赖注入，唯一需要的就是处理 CreateEntry() 的返回值。 CreateEntry 返回的条目需要被释放。上 dispose，它被添加到缓存中：

using (var entry = cache.CreateEntry("item2")) { 
    entry.Value = 2; 
    entry.AbsoluteExpiration = DateTime.UtcNow.AddDays(1); 
}

Answer 2

IMemoryCache cache = new MemoryCache(new MemoryCacheOptions());
object result = cache.Set("Key", new object());
bool found = cache.TryGetValue("Key", out result);

在 GitHub 中查看完整的 Memory Cache Sample。

您需要在项目中添加 NuGet Microsoft.Extensions.Caching.Memory 包以供使用 MemoryCache

Answer 3

这是 .NET Core 中完整的控制台应用程序代码

using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.Primitives;
using System;

using System.Threading;

namespace InMemoryNetCore
{
   class Program
  {
      static void Main(string[] args)
     {
        IMemoryCache cache = new MemoryCache(new MemoryCacheOptions());
        object result;
        string key = "KeyName";
  

        // Create / Overwrite
        result = cache.Set(key, "Testing 1");
        result = cache.Set(key, "Update 1");

        // Retrieve, null if not found
        result = cache.Get(key);
        Console.WriteLine("Output of KeyName Value="+result);

        // Check if Exists
        bool found = cache.TryGetValue(key, out result);

        Console.WriteLine("KeyName Found=" + result);

        // Delete item
        cache.Remove(key);


        //set item with token expiration and callback
        TimeSpan expirationMinutes = System.TimeSpan.FromSeconds(0.1);
        var expirationTime = DateTime.Now.Add(expirationMinutes);
        var expirationToken = new CancellationChangeToken(
            new CancellationTokenSource(TimeSpan.FromMinutes(0.001)).Token);

        // Create cache item which executes call back function
        var cacheEntryOptions = new MemoryCacheEntryOptions()
       // Pin to cache.
       .SetPriority(Microsoft.Extensions.Caching.Memory.CacheItemPriority.Normal)
       // Set the actual expiration time
       .SetAbsoluteExpiration(expirationTime)
       // Force eviction to run
       .AddExpirationToken(expirationToken)
       // Add eviction callback
       .RegisterPostEvictionCallback(callback: CacheItemRemoved);
        //add cache Item with options of callback
        result = cache.Set(key,"Call back cache Item", cacheEntryOptions);


        Console.WriteLine(result);



        Console.ReadKey();

    }

    private static void CacheItemRemoved(object key, object value, EvictionReason reason, object state)
    {
        Console.WriteLine(key + " " + value + " removed from cache due to:" + reason);
      }
   }
}

来源：In Memory cache C# (Explanation with example in .NET and .NET Core)

Answer 4

对于上面的回复，我想为常见的缓存操作添加一些简洁的替代方案：

using Microsoft.Extensions.Caching.Memory;

// ... (further down) ...
MemoryCache cache = new MemoryCache(new MemoryCacheOptions() );

// get a value from the cache
// both are equivalent
// obviously, replace "string" with the correct type
string value = (string)cache.Get("mykey");
string value = cache.Get<string>("mykey");

// setting values in the cache
// no expiration time
cache.Set("mykey", myVar);

// absolute expiration numMinutes from now
cache.Set("mykey", myVar, DateTimeOffset.Now.AddMinutes(numMinutes));

// sliding expiration numMinutes from now
// "sliding expiration" means that if it's accessed within the time period,
//      the expiration is extended
MemoryCacheEntryOptions options = new MemoryCacheEntryOptions();
options.SetSlidingExpiration(TimeSpan.FromMinutes(numMinutes));
webcache.Set("mykey", myVar, options);

// or, if you want to do it all in one statement:
webcache.Set("mykey", myVar, 
    new MemoryCacheEntryOptions {SlidingExpiration = TimeSpan.FromMinutes(numMinutes)});

Answer 5

在 Asp 网络核心控制器的 AutomaticTest 上下文中，我在测试准备设置中分配了一个 MemoryCache 实例，如下所示：

    TestCaseController _sut;
    long? NO_SIZE_LIMIT = null;

    [SetUp]
    public void Setup()
    {
        var options = new MemoryCacheOptions() 
        { 
            Clock = new SystemClock(), 
            CompactionPercentage = 1, 
            ExpirationScanFrequency = TimeSpan.FromSeconds(100), 
            SizeLimit = NO_SIZE_LIMIT
        };
        IOptions<MemoryCacheOptions> optionsAccessor = Options.Create(options);
        IMemoryCache memoryCache= new MemoryCache(optionsAccessor);
        _sut = new TestCaseController(memoryCache);
    }

目标控制器然后像这样使用缓存：

    [HttpGet("Active")]
    public IEnumerable<TestCase> GetActive()
    {
        LogRequest();
        IEnumerable<TestCase> ret;
        var cacheKey = "TestCaseActive";
        if (!_memoryCache.TryGetValue(cacheKey, out ret))
        {
            ret = _dbRepo.GetActive();
            var cacheExpiryOptions = new MemoryCacheEntryOptions
            {
                AbsoluteExpiration = DateTime.Now.AddSeconds(60),
                Priority = CacheItemPriority.High,
                SlidingExpiration = TimeSpan.FromSeconds(50)
            };
            _memoryCache.Set(cacheKey, ret, cacheExpiryOptions);
        }
        else
        {
            _log.Debug("Fetch Cache");
        }
        _log.Debug(ret.Count() + " items returned");
        return ret;
    }