为什么要在ASP.Net Core中获取多个IMemoryCache实例？

问题描述

我相信我的ASP.NET Core应用程序中有IMemoryCache的标准用法。

I have what I believe is a standard usage of IMemoryCache in my ASP.NET Core application.

在startup.cs中，我有：

In startup.cs I have:

services.AddMemoryCache();

在我的控制器中，我有：

In my controllers I have:

private IMemoryCache memoryCache;
public RoleService(IMemoryCache memoryCache)
{
    this.memoryCache = memoryCache;
}

但是，当我进行调试时，最终会得到多个具有不同每个项目。我以为内存缓存将是一个单例？

Yet when I go through debug, I end up with multiple memory caches with different items in each one. I thought memory cache would be a singleton?

已更新代码示例：

public List<FunctionRole> GetFunctionRoles()
{
    var cacheKey = "RolesList";
    var functionRoles = this.memoryCache.Get(cacheKey) as List<FunctionRole>;
    if (functionRoles == null)
    {
         functionRoles = this.functionRoleDAL.ListData(orgId);
         this.memoryCache.Set(cacheKey, functionRoles, new MemoryCacheEntryOptions().SetAbsoluteExpiration(TimeSpan.FromDays(1)));
    }
}

如果我在两个不同的浏览器中运行两个客户端，当我点击第二行，可以看到this.memoryCache包含不同的条目。

If I run two clients in two different browsers, when I hit the second line I can see this.memoryCache contains different entries.

推荐答案

多次创建IMemoryCache的原因是

The reason that IMemoryCache is created multiple times is that your RoleService most likely gets scoped dependencies.

要修复此问题，只需添加一个包含内存缓存的新单例服务并在需要时插入，而不是IMemoryCache：

To fix it simply add a new singleton service containing the memory cache and inject in when needed instead of IMemoryCache:

// Startup.cs:

services.AddMemoryCache();
services.AddSingleton<CacheService>();

// CacheService.cs:

public IMemoryCache Cache { get; }

public CacheService(IMemoryCache cache)
{
  Cache = cache;
}

// RoleService:

private CacheService cacheService;
public RoleService(CacheService cacheService)
{
    this.cacheService = cacheService;
}

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