C#使用动态构造的事件处理程序处理DDD域事件
作者:互联网
我正在使用带有EF Core 2.0的ASP.NET Core 2.0构建应用程序.至于在我的域中解耦不同种类的逻辑,我使用DDD(域驱动设计)的域事件.让我们深入研究实现,看看有什么,然后我将讨论我的问题.
首先,让我们看一下与域事件相关的类的通用实现.首先是标记接口IDomainEvent:
public interface IDomainEvent
{
}
在它旁边,我有一个通用的IHandler类:
public interface IHandler<in T> where T : IDomainEvent
{
void Handle(T domainEvent);
}
然后,我有一个DomainEvents类:
private static List<Type> _handlers;
public static void Init()
{
InitHandlersFromAssembly();
}
private static void InitHandlersFromAssembly()
{
_handlers = Assembly.GetExecutingAssembly()
.GetTypes()
.Where(x => x.GetInterfaces().Any(y => y.IsGenericType && y.GetGenericTypeDefinition() == typeof(IHandler<>)))
.ToList();
}
public static void Dispatch(IDomainEvent domainEvent)
{
foreach (var handlerType in _handlers)
{
if (CanHandleEvent(handlerType, domainEvent))
{
dynamic handler = Activator.CreateInstance(handlerType);
handler.Handle((dynamic)domainEvent);
}
}
}
private static bool CanHandleEvent(Type handlerType, IDomainEvent domainEvent)
{
return handlerType.GetInterfaces()
.Any(x => x.IsGenericType
&& x.GetGenericTypeDefinition() == typeof(IHandler<>)
&& x.GenericTypeArguments[0] == domainEvent.GetType());
}
如您所见,DomainEvents类将初始化执行程序集的所有域事件.在域的自定义DbContext的重写SaveChanges()方法中调用Dispatch方法.我在此调用调度,以便在工作单元的事务处调度所有事件:
public override int SaveChanges()
{
DomainEventsDispatcher.Dispatch(ChangeTracker);
return base.SaveChanges();
}
并执行DomainEventDispatcher:
public static class DomainEventsDispatcher
{
public static void Dispatch(ChangeTracker changeTracker)
{
var domainEvents = GetDomainEventEntities(changeTracker);
HandleDomainEvents(domainEvents);
}
private static IEnumerable<IEntity> GetDomainEventEntities(ChangeTracker changeTracker)
{
return changeTracker.Entries<IEntity>()
.Select(po => po.Entity)
.Where(po => po.Events.Any())
.ToArray();
}
private static void HandleDomainEvents(IEnumerable<IEntity> domainEventEntities)
{
foreach (var entity in domainEventEntities)
{
var events = entity.Events.ToArray();
entity.Events.Clear();
DispatchDomainEvents(events);
}
}
private static void DispatchDomainEvents(IDomainEvent[] events)
{
foreach (var domainEvent in events)
{
DomainEvents.Dispatch(domainEvent);
}
}
到目前为止,它可以与简单的域事件处理程序很好地协同工作,例如:
public class OrderCreatedEventHandler : IHandler<OrderCreatedEvent>
{
public void Handle(OrderCreatedEvent domainEvent)
{
Console.WriteLine("Order is created!");
}
}
但是我还有其他一些事件处理程序,我想在其中注入某种依赖性,即存储库:
public class OrderCreatedEventHandler : IHandler<OrderCreatedEvent>
{
private readonly IOrderHistoryRepository _orderHistoryRepository;
public OrderCreatedEventHandler(IOrderHistoryRepository orderHistoryRepository)
{
_orderHistoryRepository = orderHistoryRepository;
}
public void Handle(OrderCreatedEvent domainEvent)
{
_orderHistoryRepository.Insert(new OrderHistoryLine(domainEvent));
}
}
我的问题如下:在DomainEvents类Dispatch方法中,我使用Activator类在运行时动态构造事件处理程序.在这一行,抛出异常并显示以下消息:
System.MissingMethodException: 'No parameterless constructor defined for this object.'
这是合乎逻辑的,因为在OrderCreatedEventHandler中,只有一个构造函数注入了存储库.我的问题是:是否可以在动态构造的处理程序中注入该存储库?如果不是,什么是我的问题的解决方案或解决方法?
附加信息:
作为IoC框架,我使用Autofac,并在Startup.cs中对其进行配置,其中还初始化了域事件:
// This method gets called by the runtime. Use this method to add services to the container.
public IServiceProvider ConfigureServices(IServiceCollection services)
{
services.AddMokaKukaTrackerDbContext(CurrentEnvironment, Configuration);
services.RegisterIdentityFramework();
services.AddAndConfigureMvc(CurrentEnvironment);
var autofacServiceProvider = new AutofacServiceProvider(CreateIoCContainer(services));
DomainEvents.Init();
return autofacServiceProvider;
}
private static IContainer CreateIoCContainer(IServiceCollection services)
{
var builder = new ContainerBuilder();
builder.Populate(services);
builder.RegisterModule(new AutofacInjectorBootstrapperModule());
return builder.Build();
}
如果您需要有关我的问题的更多信息/代码,请告诉我,然后尽快将其包括在内.提前致谢!
解决方法:
解决方案是使用依赖注入容器创建具有依赖关系的对象的实例.为此,您需要将IContainer向下传递到DomainEvents实例,即作为参数传递给DomainEvents.Init()方法调用.
// This method gets called by the runtime. Use this method to add services to the container.
public IServiceProvider ConfigureServices(IServiceCollection services)
{
services.AddMokaKukaTrackerDbContext(CurrentEnvironment, Configuration);
services.RegisterIdentityFramework();
services.AddAndConfigureMvc(CurrentEnvironment);
var container = CreateIoCContainer(services);
var autofacServiceProvider = new AutofacServiceProvider(container);
DomainEvents.Init(container);
return autofacServiceProvider;
}
然后,DomainEvents类应该存储对该容器的引用,并在Dispatch方法中使用它.
注意1:我没有使用C#的丰富经验,所以我不确定是否应该将IContainer或IServiceProvider注入DomainEvents.
注意2:正如@TSeng在评论中所说,请尽量不要使用静态方法;重构为使用类的实例.
标签:asp-net-core,domain-driven-design,c,autofac 来源: https://codeday.me/bug/20191025/1926501.html