c# - IDistributedCache 可用但数据不再在缓存中？

Question

我正在使用 services.AddDistributedMemoryCache()在我的 .Net Core 3 Web API 中 startup.cs类(class)。当我第一次设置缓存时:

public void SetCommandEventMappingCache(IServiceCollection serviceCollection)
{
    var cache = serviceCollection.BuildServiceProvider().GetService<IDistributedCache>();

    var mappingList = new List<CommandEventMapping>()
    {
        new CommandEventMapping()
        {
            ActionType = "add",
            GrowFlowCommand = new AddEmployee(),
            GrowFlowEvent = "EmployeeAdded",
            TraceabilityCommand = "employee_add"
        }
    };

    cache.Set<List<CommandEventMapping>>(
        "command_event_mappings", mappingList,new DistributedCacheEntryOptions()
    {
        AbsoluteExpiration = DateTimeOffset.Now.AddDays(1)
    });

    //I am able to get back the command_event_mappings here.
    //Once the IDistributedCache is injected. the data is lost
    var commandMapping = cache.Get<List<CommandEventMapping>>("command_event_mappings");
}

在我见过的所有示例中，通常都是这样设置的。唯一的区别是我为 Set<T> 添加了几个扩展名。和 Get<T> .我确实在没有新扩展方法的情况下进行了尝试，但结果相同。实际IDistributedCache注入(inject)的时候是可用的，但是之前缓存的数据没有了。这是我如何注入(inject)它的示例。

public LegacyCommandBus(IServiceProvider provider, IDistributedCache cache,
    ITraceabilityTenantService tenantService, IHttpClientFactory httpClientFactory)
    : base(provider)
{
    _provider = provider;
    _cache = cache;
    _tenantService = tenantService;
    _httpClientFactory = httpClientFactory; 
    //This is null
    _commandEventMappings = cache.Get<List<CommandEventMapping>>("command_event_mappings");
}

Answer 1

var cache = serviceCollection.BuildServiceProvider().GetService<IDistributedCache>();

每次调用 BuildServiceProvider() 时，您都会生成一个新容器，它有自己的一组单例(不同于使用内置 DI 注入(inject)的单例)。

解决方案是在 Startup 类的 Configure 中解析 IDistributedCache 的实例。

public void Configure(IApplicationBuilder app, IDistributedCache cache) { 
    //...
}