为什么 autofac 在 HttpRequest 结束之前处理对象？

Question

我正在编写一个 ASP.NET MVC 网站，使用 autofac 进行依赖注入，并使用 Mindscape 的 Lightspeed 作为 ORM。有一个 UserRepository 类，它依赖于光速 UnitOfWork，并为 Logon 控制器提供服务。

问题：UnitOfWork 在 UserRepository 使用完毕之前就被释放了。

  public class UserRepository : IUserRepository
  {
    private readonly BluechipModelUnitOfWork _unitOfWork;

    public UserRepository(BluechipModelUnitOfWork unitOfWork)
    {
        _unitOfWork = unitOfWork;
    }
    public Principal GetPrincipal(string name)
    {
        // This line throws an ObjectDisposedException - UnitOfWork is already disposed.
        return _unitOfWork.Principals.FirstOrDefault(p => p.Name == name);
    }
    ...

在 Global.asax 中，依赖关系连接如下完成：

public class MvcApplication : HttpApplication, IContainerProviderAccessor
{
    private static void RegisterAutofac()
    {
        var builder = new ContainerBuilder();

        // Register the lightspeed context as a singleton
        builder.RegisterInstance(new LightSpeedContext<BluechipModelUnitOfWork>("LightSpeedBluechip"))
            .As<LightSpeedContext<BluechipModelUnitOfWork>>()
            .SingleInstance();

        // Register the unit of work constructor so that a new instance is bound to each HttpRequest
        builder.Register(c => c.Resolve<LightSpeedContext<BluechipModelUnitOfWork>>().CreateUnitOfWork())
            .As<BluechipModelUnitOfWork>()
            .InstancePerLifetimeScope();

        // Register user repository to be one instance per HttpRequest lifetime
        builder.Register(c => new UserRepository(c.Resolve<BluechipModelUnitOfWork>()))
            .As<IUserRepository>()
            .InstancePerLifetimeScope();

        builder.Register(c => new CurrentUserService(
                                  c.Resolve<HttpSessionState>(),
                                  c.Resolve<IUserRepository>(),
                                  c.Resolve<IMembershipService>())
            ).As<ICurrentUserService>()
            .CacheInSession();

        builder.RegisterType<ExtensibleActionInvoker>().As<IActionInvoker>();
        builder.RegisterControllers(Assembly.GetExecutingAssembly()).PropertiesAutowired().InjectActionInvoker();
        builder.RegisterModelBinders(Assembly.GetExecutingAssembly());

        // Set the container provider up with registrations.    
        _containerProvider = new ContainerProvider(builder.Build());

        // Set the controller factory using the container provider.    
        ControllerBuilder.Current.SetControllerFactory(new AutofacControllerFactory(_containerProvider));

鉴于上述注册，为什么 autofac 会处置 UnitOfWork (

Answer 1

我能够找到问题所在——这是一个愚蠢但微妙的陷阱......
我有一个 CurrentUserService 类，我注册如下：

    builder.Register(c => new CurrentUserService(
                                  c.Resolve<HttpSessionState>(),
                                  c.Resolve<IUserRepository>(),
                                  c.Resolve<IMembershipService>())
            ).As<ICurrentUserService>()
            .CacheInSession();

问题是 CacheInSession()，因为 CurrentUserService 依赖于 IUserRepository，autofac 忠实地注入了该类，但随后在第一个请求结束时进行了处理。

这揭示了一些显而易见的事情，但在连接依赖项注入时需要注意一些微妙的事情：

确保高阶依赖项始终与它们所依赖的服务具有相同或更短的生命周期。就我而言，解决方案是更改上面的代码：

        builder.Register(c => new CurrentUserService(
                                  c.Resolve<HttpSessionState>(),
                                  c.Resolve<IUserRepository>(),
                                  c.Resolve<IMembershipService>())
            ).As<ICurrentUserService>()
            .InstancePerLifetimeScope();

.... 这可以防止 CurrentUserService 超出它所依赖的实例的寿命。