Question

我有两个装饰器：

class DbCommandWithTransactionHandlerDecorator<TCommand>
    : IDbCommandHandler<TCommand> { ... }

class DbOptimisticConcurrencyRetryDecorator<TCommand>
    : IDbCommandHandler<TCommand> { ... }

这些装饰器为数据库命令添加了事务管理和乐观并发重试功能。

我使用Autofac作为我的IoC容器。我想设置Autofac，它会自动连接程序集中找到的所有IDbCommandHandler<>，这样当我请求说IDbCommandHandler<CreateNewNotificationCommand>时，它会自动装饰它DbCommandWithTransactionHandlerDecorator ，然后是DbOptimisticConcurrencyRetryDecorator。

我一直试图通过Autofac的builder.RegisterGenericDecorator()来解决这个问题，但还没有完成管理。主要问题是装饰器需要“命名”参数才能工作。下面是最接近我想要实现的示例代码 - 但主要的缺陷是我仍然需要手动注册类型。

var builder = new ContainerBuilder();
var a = Assembly.GetExecutingAssembly();

// I need to find a way how these can be 'auto-wired', 
// rather than having to manually wire each command.

builder.RegisterType<CreateNewNotificationCommandHandler>()
    .Named<IDbCommandHandler<CreateNewNotificationCommand>>("command");
builder.RegisterType<CreateNewNotificationCommandHandler_2>()
    .Named<IDbCommandHandler<CreateNewNotificationCommand_2>>("command");

builder.RegisterGenericDecorator(
    typeof(DbCommandWithTransactionHandlerDecorator<>),
    typeof(IDbCommandHandler<>),
    fromKey: "command");

var container = builder.Build();
var handler1 =
  container.Resolve<IDbCommandHandler<CreateNewNotificationCommand>>();
var handler2 =
  container.Resolve<IDbCommandHandler<CreateNewNotificationCommand_2>>();
handler1.Handle(null); //these are correctly decorated
handler2.Handle(null); //these are correctly decorated

Answer 1

我确实设法通过反射找到了一种解决方法，虽然它的工作原理并不是很优雅。为了完整起见，我将在下面发布：

 public interface IDbCommandHandler<in TCommand>: IDbCommandHandlerStub
    where TCommand : IDbCommand
{
    void Handle(TCommand command);
}

public interface IDbCommandHandlerStub
{

}

    private List<Type> getTypesThatImplementIDbCommandHandler(IEnumerable<Assembly> assemblyList)
    {
        List<Type> list = new List<Type>();
        foreach (var a in assemblyList)
        {
            var matches = a.GetTypes().Where(t => typeof(IDbCommandHandlerStub).IsAssignableFrom(t));
            list.AddRange(matches);
        }
        return list;
    }

private void registerDbCommands(List<Type> dbCommandHandlerTypes, ContainerBuilder builder)
    {
        foreach (var t in dbCommandHandlerTypes)
        {
            var interfaces = t.GetInterfaces();
            foreach (var i in interfaces)
            {
                builder.RegisterType(t).Named("dbCommand", i);
            }

        }
    }


   public void Test1()
   {
        ContainerBuilder builder = new ContainerBuilder();
        var dbCommandHandlerTypes = getTypesThatImplementIDbCommandHandler(assemblies);
        registerDbCommands(dbCommandHandlerTypes, builder);            

        builder.RegisterGenericDecorator(typeof(DbCommandWithTransactionHandlerDecorator<>),
                                        typeof(IDbCommandHandler<>),
                                        fromKey: "dbCommand", toKey:"dbCommandWithTransaction").SingleInstance();

        builder.RegisterGenericDecorator(typeof(DbOptimisticConcurrencyRetryDecorator<>),
                                        typeof(IDbCommandHandler<>),
                                        fromKey: "dbCommandWithTransaction").SingleInstance();

        var container = builder.Build();
        var handler1 = container.Resolve<IDbCommandHandler<CreateNewNotificationCommand>>();

}

首先，我通过反思了所有实现IDbCommandHandler的类型。然后，我将它们注册为它们实现的所有接口的命名类型，给它们命名为“dbCommand”。

然后，我注册通用装饰器来装饰名为'dbCommand'的类型。这个decorater名为'dbCommandWithTransaction'，然后用于为并发重试注册另一个通用装饰器。

考虑到这是可以做一次并且“忘记”的事情，我已经准备好了解这个解决方法。但是，我正在尝试其他IoC容器并且遇到了Simple Injector，所有这些只需要两行代码即可完成 - 从那时起我就赢了。

使用Autofac自动连接通用装饰器

1 个答案: