我正在使用ASP.NET Core2.0和EF Core2.0构建一个应用程序。至于在我的领域中对不同类型的逻辑进行解耦,我使用了DDD (域驱动设计)的域事件。让我们深入到实现中,看看我有什么,然后我将讨论我的问题。首先,让我们看看与域事件相关的类的通用实现。首先是一个标记接口,IDomainEvent
public interface IDomainEvent
{
}
在它旁边有一个通用的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());
}
正如您所看到的,DomainEvents
类初始化正在执行的程序集的所有域事件。在我的域的自定义DbContext
的重写的SaveChanges()
方法中调用Dispatch
方法。我在这里调用调度,以便在一个工作单元的事务处理结束时调度所有事件:
public override int SaveChanges()
{
DomainEventsDispatcher.Dispatch(ChangeTracker);
return base.SaveChanges();
}
以及DomainEventDispatcher
的实现
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,它与简单的域事件处理程序一起工作得很好,例如:
public class OrderCreatedEventHandler : IHandler<OrderCreatedEvent>
{
public void Handle(OrderCreatedEvent domainEvent)
{
Console.WriteLine("Order is created!");
}
}
但我有一些其他的事件处理程序,我想在其中注入一些依赖项,即Repository:
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。在此行抛出异常,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
中只有一个注入了存储库的构造函数。我的问题是:是否可以将该存储库注入到我的动态构造的处理程序中?如果不是,我的问题有什么解决方案或变通方法?
其他信息:
作为IoC框架,我使用Autofac,并且我在Startup.cs
中配置了它,域事件也是在这里初始化的:
// 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();
}
如果您需要更多关于我的问题的信息/代码,请让我知道,然后我会尽快将它们包括在内。提前感谢!
发布于 2018-05-24 06:54:07
我决定按照@Devesh Tipe的要求放置我的最终解决方案。批准的解决方案解决了我的问题,但我已经在我的代码库中进行了几次重构,以便以更优雅的方式处理域事件。使用以下解决方案,我们能够创建具有依赖关系的域处理程序,这些依赖关系在运行时通过Autofac依赖关系框架解决。让我们深入研究代码,包括整个解决方案:
首先,我有一个域事件的标记接口:
public interface IDomainEvent
{
}
然后我有一个对域处理程序的接口:
public interface IHandler<in T> where T : IDomainEvent
{
void Handle(T domainEvent);
}
此外,我有一个负责分派/处理一个事件的EventDispatcher
:
public class EventDispatcher : IEventDispatcher
{
private readonly ILifetimeScope _lifetimeScope;
public EventDispatcher(ILifetimeScope lifetimeScope)
{
_lifetimeScope = lifetimeScope;
}
public void Dispatch<TEvent>(TEvent eventToDispatch) where TEvent : IDomainEvent
{
foreach (dynamic handler in GetHandlers(eventToDispatch))
{
handler.Handle((dynamic)eventToDispatch);
}
}
private IEnumerable GetHandlers<TEvent>(TEvent eventToDispatch) where TEvent : IDomainEvent
{
return (IEnumerable) _lifetimeScope.Resolve(
typeof(IEnumerable<>).MakeGenericType(
typeof(IHandler<>).MakeGenericType(eventToDispatch.GetType())));
}
}
正如您所看到的,这里检索并调用了具有已解析依赖关系的相应处理程序。此调度程序在executor类中使用,如:
public class DomainEventHandlingsExecutor : IDomainEventHandlingsExecutor
{
private readonly IEventDispatcher _domainEventDispatcher;
public DomainEventHandlingsExecutor(IEventDispatcher domainEventDispatcher)
{
_domainEventDispatcher = domainEventDispatcher;
}
public void Execute(IEnumerable<IEntity> domainEventEntities)
{
foreach (var entity in domainEventEntities)
{
var events = entity.Events.ToArray();
entity.Events.Clear();
foreach (var @event in events)
{
_domainEventDispatcher.Dispatch(@event);
}
}
}
}
它被注入到我的数据库上下文中:
public MokaKukaTrackerDbContext(DbContextOptions<MokaKukaTrackerDbContext> options, IDomainEventHandlingsExecutor domainEventHandlingsExecutor) : base(options)
{
_domainEventHandlingsExecutor = domainEventHandlingsExecutor;
}
public override int SaveChanges()
{
var numberOfChanges = base.SaveChanges();
_domainEventHandlingsExecutor.Execute(GetDomainEventEntities());
return numberOfChanges;
}
private IEnumerable<IEntity> GetDomainEventEntities()
{
return ChangeTracker.Entries<IEntity>()
.Select(po => po.Entity)
.Where(po => po.Events.Any())
.ToArray();
}
最后但并非最不重要的一点是,我在AutofacModule
中注册了与域事件处理相关的所有处理程序和逻辑:
public class AutofacEventHandlingBootstrapperModule : Module
{
protected override void Load(ContainerBuilder builder)
{
builder.RegisterType<EventDispatcher>().As<IEventDispatcher>().InstancePerLifetimeScope();
builder.RegisterType<DomainEventHandlingsExecutor>().As<IDomainEventHandlingsExecutor>().InstancePerLifetimeScope();
RegisterEventHandlersFromDomainModel(builder);
}
private static void RegisterEventHandlersFromDomainModel(ContainerBuilder builder)
{
var domainModelExecutingAssembly = new DomainModelExecutingAssemblyGetter().Get();
builder.RegisterAssemblyTypes(domainModelExecutingAssembly)
.Where(t => t.GetInterfaces().Any(i => i.IsClosedTypeOf(typeof(IHandler<>))))
.AsImplementedInterfaces()
.InstancePerLifetimeScope();
}
}
当然,它们必须在Startup.cs
中注册
public IServiceProvider ConfigureServices(IServiceCollection services)
{
services.AddMokaKukaTrackerDbContext(CurrentEnvironment, Configuration);
return new AutofacServiceProvider(CreateIoCContainer(services));
}
private static IContainer CreateIoCContainer(IServiceCollection services)
{
var builder = new ContainerBuilder();
builder.Populate(services);
builder.RegisterModule(new AutofacInjectorBootstrapperModule());
builder.RegisterModule(new AutofacEventHandlingBootstrapperModule());
return builder.Build();
}
就是这样,我希望它能帮助一些人!
https://stackoverflow.com/questions/50438497
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