Autofac 的强制依赖

Question

我正在寻找使用 autofac 解决 Captive Dependency 问题的最简洁方法。

我有一个短期课程，将根据 LifeTimeScope 注册：

public class ShortLived
{
    public void DoSomethingUsefull() {}
}

我有一个长寿类，它将被注册为单个实例。它依赖于 ShortLived 类：

public class LongLived
{
    private readonly Func<ShortLived> _getCurrentShortLived;

    public LongLived(Func<ShortLived> getCurrentShortLived)
    {
        _getCurrentShortLived = getCurrentShortLived;
    }

    public void DoSomethingWithShortLived()
    {
        var currentShortLived = _getCurrentShortLived();
        currentShortLived.DoSomethingUsefull();
    }
}

以下尝试无效。它会抛出 Autofac.Core.DependencyResolutionException。

public void CaptiveDependencyTest()
{
    var builder = new ContainerBuilder();
    builder.RegisterType<LongLived>()
        .SingleInstance();
    var container = builder.Build();

    using (var scope = container.BeginLifetimeScope(b => b.RegisterType<ShortLived>()))
    {
        var longLived = scope.Resolve<LongLived>();
        longLived.DoSomethingWithShortLived();
    }
}

以下确实有效。但我真的希望有一个比依赖某种静态变量更好的解决方案。

private static ILifetimeScope currentLifetimeScope;

public void CaptiveDependencyTest2()
{
    var builder = new ContainerBuilder();
    builder.Register(c =>
    {
        Func<ShortLived> shortLivedFacotry = () => currentLifetimeScope.Resolve<ShortLived>();
        return new LongLived(shortLivedFacotry);
    })
    .SingleInstance();
    var container = builder.Build();

    using (var scope = container.BeginLifetimeScope(b => b.RegisterType<ShortLived>()))
    {
        currentLifetimeScope = scope;
        var longLived = scope.Resolve<LongLived>();
        longLived.DoSomethingWithShortLived();
    }
}

一些背景信息： 我正在开发 OWIN 托管的 ASP.Net WebApi2 微服务。调用其他服务时，我需要从 currentOwinContext.Request.User.Identity 读取值并将它们添加到我发送给下一个服务的 RequestMessage 中。我的 LongLived 类是一个 DelegatingHandler（即 HttpClient“HttpMessageHandler-Pipeline”的一部分），并且 HttpClient 需要是 .SingleInstance() 所以我不必为我发出的每个请求实例化新的 HttpClients。 ShortLived 类是 IOwinContext，它注册在 Owin Pipeline 的 LifeTimeScope 中。

我可以在 autofac 中注册 HttpConfiguration，而不是 currentLifeTimeScope 的静态变量。然后我可以使用 httpConfig.DependencyResolver.GetRequestLifetimeScope(); 获得 currentLifeTimeScope我还没有测试过这种方法。我仍然希望找到更干净的东西。

Answer 1

如果类型 T 注册到容器中，Autofac 将自动解析对 Func 的依赖，作为通过容器创建 T 实例的工厂，请查找有关委托工厂的更多信息

如下所示注册您的 ShortLived 课程，现在一切正常。

public void CaptiveDependencyTest()
{
    var builder = new ContainerBuilder();
    builder.RegisterType<ShortLived>()
        .SingleInstance();
    builder.RegisterType<LongLived>()
        .SingleInstance();
    var container = builder.Build();

    //using (var scope = container.BeginLifetimeScope(b => b.RegisterType<ShortLived>()))
    //{
        var longLived = container.Resolve<LongLived>();
        longLived.DoSomethingWithShortLived();
    //}
}

你也可以直接从容器中解析，不再需要使用，但最终选择是你的

Answer 2

在 ASP.NET Core 中，HttpContext 类提供属性 public IServiceProvider RequestServices { get; set; }。即使您只有对根生命周期范围的引用，这也可用于解决请求生命周期范围的依赖关系。诀窍是记住ILifetimeScope 可以从任何IComponentContext 解析。这种行为可以封装在下面的扩展方法中。

public static ILifetimeScope GetLifetimeScope(this HttpContext httpContext)
{
   return httpContext.RequestServices.GetService(typeof(ILifetimeScope)) as ILifetimeScope;
}

现在您可以使用以下代码轻松进入“每个请求”生命周期范围，给定IComponentContext 的实例。

ctx => {
  var requestScope = ctx.Resolve<IHttpContextAccessor>().HttpContext.GetLifetimeScope();

  var shortLived = requestScope.Resolve<ShortLived>();
}

---

---

在传统的 ASP.NET 中，存在“依赖解析器”而不是“服务提供者”。

例如GlobalConfiguration.Configuration.DependencyResolver = 在这里集成 autofac

解决ILifetimeScope 有点麻烦。

public static ILifetimeScope GetLifetimeScope(this HttpContext httpContext)
{
    var requestMessage = httpContext.Items["MS_HttpRequestMessage"] as HttpRequestMessage;

    return requestMessage?.GetDependencyScope().GetService(typeof(ILifetimeScope)) as ILifetimeScope;
}

var requestScope = HttpContext.Current.GetLifetimeScope();

var shortLived = requestScope.Resolve<ShortLived>();