在 .NET Core 2 中存储和检索 IDistributedCache (Redis) 中的值

Question

我有一个 ASP.NET Core2 应用程序。我同时使用内置和 Autofac IoC 容器。我正在 Startup.cs 文件中设置所有组件注册。在执行此操作时，我还设置了我的 DBContext，它继承自自定义 DataContext，后者又继承自 DbContext 并实现自定义 IDataContextAsync。此 DbContext 需要连接字符串作为构造函数参数。

我的问题是连接字符串存储在 IDistributedCache 的 Redis 缓存中。缓存设置在 startup.cs 文件中。 Startup.cs 中的同一 ConfigureServices 方法也需要连接字符串。所以，我现在似乎无法访问这个缓存。

当我使用 HttpContext Session 存储连接字符串时，一切正常。现在应用程序正在部署到 Web 场，我不能在 proc 会话中使用。我们使用 Redis 进行状态管理。这是我遇到问题的地方。

这是 startup.cs 文件中的 ConfigureServices 方法（为简洁起见删除了不必要的代码）。

public IServiceProvider ConfigureServices(IServiceCollection services)
{
   services.AddMvc()
      .AddJsonOptions(op => op.SerializerSettings.ContractResolver = new DefaultContractResolver());

   services.AddSession(opt =>
  {
     opt.IdleTimeout = TimeSpan.FromMinutes(20);
     opt.Cookie.Name = "apexportal.RulesSession";
     opt.Cookie.HttpOnly = true;
  });

   services.AddDistributedRedisCache(o =>
  {
     var host = Configuration.GetValue<string>($"{AppConstants.REDIS}:{AppConstants.REDISHOST}");
     var port = Configuration.GetValue<string>($"{AppConstants.REDIS}:{AppConstants.REDISPORT}");
     o.Configuration = $"{host}";
     o.InstanceName = Configuration.GetValue<string>($"{AppConstants.REDIS}:{AppConstants.REDISNAME}");
  });

   services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
   //services.AddTransient<IConnectionStringProvider, ConnectionStringProvider>();
   services.AddTransient<IDataContextAsync>(s => new PortalEFContext(GetPortalConnectionString()));
   services.AddAuthentication(IISDefaults.AuthenticationScheme);

   ContainerBuilder builder = new ContainerBuilder();
   builder.Populate( services );
   var container = builder.Build();

   return container.Resolve<IServiceProvider>();
}

这是我的 GetPortalConnectionString() 方法，它也在 startup.cs 文件中。我想用注入的 RedisCache.Get().

替换行 accessor.HttpContext.Session.Get()

private string GetPortalConnectionString()
{
   IHttpContextAccessor accessor = new HttpContextAccessor();

   //this is where I need to access the RedisCache and access the stored properties
   // instead of using HttpContext.Session.  But I don't know how to inject the IDistributedCache 
   // to this spot.
   var connString = accessor.HttpContext.Session.Get<string>(AppConstants.SPCONNSTRING);

   return connString ?? Configuration.GetConnectionString("PortalEFContext");
}

稍后，当用户选择要在应用程序中使用的数据库时，我会像这样在 Redis 缓存中存储到该数据库的连接字符串。

这是我的 BaseController class 做的。

public abstract class BaseController : Controller
{
  //private readonly IRulesEngineService reService;
  protected readonly IHttpContextAccessor httpCtxAccessor;
  protected readonly IConfiguration config;
  private readonly IAuthService authService;
  protected readonly IDistributedCache redisCache;

  public BaseController(IHttpContextAccessor _httpContext, IConfiguration _config, IAuthService _authService, IDistributedCache _redisCache)
  {
     //reService = _reService;
     httpCtxAccessor = _httpContext;
     config = _config;
     authService = _authService;
     redisCache = _redisCache;
     //SetupCurrentWindowsUserAsync();
  }

  protected async Task<string> SetCurrentDBConnString( int dbId )
  {
     var currDbId = await GetCurrentDBId();

     if ( currDbId == 0 || currDbId != dbId )
     {
        var envConnStr = config.GetConnectionString( AppConstants.ENVCONNSTRING );
        var connStr = await AppHelper.SetCurrentDBConnectionString( dbId, envConnStr );
        //httpCtxAccessor.HttpContext.Session.Set<string>( AppConstants.SPCONNSTRING, connStr );
        //httpCtxAccessor.HttpContext.Session.Set<int>( AppConstants.CURRDBID, dbId );
        await redisCache.SetAsync<string>( AppConstants.SPCONNSTRING, connStr );
        await redisCache.SetAsync<int>( AppConstants.CURRDBID, dbId );
        await SetupCurrentWindowsUserAsync();
        return connStr;
     }
     return null;
  }
}

谁能告诉我如何访问 startup.cs 文件中的 Redis 缓存？谢谢

Answer 1

其实很简单。你快到了。

仔细看看你启动时的这一行：

services.AddTransient<IDataContextAsync>(s => new PortalEFContext(GetPortalConnectionString()));

看到 lambda 中的 s 参数了吗？这是 .NET Core 的 DI 容器，名为 IServiceProvider。这就是您要找的。只需将它传递到您的函数中，然后在那里使用它来解决您想要的任何问题。

所以，代码如下：

public IServiceProvider ConfigureServices(IServiceCollection services)

    ...

    services.AddTransient<IDataContextAsync>(s => new PortalEFContext(GetPortalConnectionString(s))); // <-- pass the container to the function

    ...

}

private string GetPortalConnectionString(IServiceProvider container)
{
    // Here you go:
    var cache = container.GetService<IDistributedCache>();

    // and now do whatever you want with it.
    var connString = cache.Get<string>(AppConstants.SPCONNSTRING);

    // BTW, configuration can be resolved from container as well in order to avoid hard dependency on global Configuration object:
    var config = container.GetService<IConfiguration>();

    return connString ?? config.GetConnectionString("PortalEFContext");
}

在 .NET Core 2 中存储和检索 IDistributedCache (Redis) 中的值

Storing and retrieving values from IDistributedCache (Redis) in .NET Core 2

asp.net-core

dependency-injection

redis

autofac

distributed-caching