在软件开发中,事件早已被我们所熟悉,一个按钮按下,产生中断事件,一个回车,前端页面有侦听事件,在事件风暴建模活动中,事件也是作为领域建模的突破口,事件的重要性不言而喻。其本质是发生的事实到引发了相关事情,在这其中的传递的信息便是事件的内容。就如同猫叫了,引发着老鼠跑了,主人醒了,其中的事件便是猫叫了,而该事件是猫执行叫的动作后的结果。
领域事件
在领域驱动设计中,最开始的版本中并没有领域事件的概念,在 DDD 社区对领域驱动设计的内容不断的充实中,引入了领域事件。领域事件的命名遵循英语中的“名词 + 动词过去分词”格式,如,提交订单后发布的 OrderCreated 事件,订单完成后 OrderCompleted 事件,用以表示我们建模的领域中发生过的一件事情,也符合着事件本身是具有时间特征。对于事件所通知到的范围的不同,领域事件本身也分为两类:
- 领域内事件,即领域事件,作用于进程内的通信。
- 领域间事件,即集成事件,作用于进程间的通信。
为实现事件的发布,可以借助一些现有的包集成到系统中,但又为了隔离使用上依赖了具体的技术实现,我们可以对其进行一定的封装。
MediatR
MediatR是.NET中的开源简单中介者模式实现,它通过一种进程内消息传递机制(无其他外部依赖),进行请求/响应、命令、查询、通知和事件的消息传递,并通过泛型来支持消息的智能调度。
https://github.com/jbogard/MediatR
Cap
CAP 本身就是一个EventBus,能处理进程内消息,同时也是一个在微服务或者SOA系统中解决分布式事务问题的一个框架。它有助于创建可扩展,可靠并且易于更改的微服务系统。
https://github.com/dotnetcore/CAP
抽象EventBus
新建EventBus.Abstractions类库,用来抽象领域事件和集成事件的发布。
dotnet new classlib --name EventBusDemo.EventBus.Abstractions
在MediatR中,有一个抽象的Contracts类库,方便我们构建一个抽象的EventBus。
MediatR发布事件时,事件类上必须要有标记,比如如下INotification标记,因此,此处增加领域事件接口约束,来隔离INotification。
using MediatR;
namespace EventBusDemo.EventBus.Abstractions.Local;
public interface IDomainEvent : INotification
{
}
本地事件EventBus, 参照MediatR中已有接口,替换约束类。
namespace EventBusDemo.EventBus.Abstractions.Local;
public interface ILocalEventBUs
{
Task Publish(IDomainEvent domainEvent, CancellationToken cancellationToken = default);
Task Publish<T>(T domainEvent, CancellationToken cancellationToken = default)
where T : IDomainEvent;
}
同样,增加集成事件,Cap框架没有限制集成事件类的约束条件,而为了能够统一标识项目中的集成事件,还是有必要设置一个接口约束。
namespace EventBusDemo.EventBus.Abstractions.Distributed;
public interface IIntegrationEvent
{
}
增加集成事件的EventBus,参照Cap框架中发布时的接口并用IIntegrationEvent来约束事件。
namespace EventBusDemo.EventBus.Abstractions.Distributed;
public interface IDistrbutedEventBus
{
Task PublishAsync<T>(string name, T? contentObj, string? callbackName = null, CancellationToken cancellationToken = default)
where T : IIntegrationEvent;
Task PublishAsync<T>(string name, T? contentObj, IDictionary<string, string?> headers, CancellationToken cancellationToken = default)
where T : IIntegrationEvent;
void Publish<T>(string name, T? contentObj, string? callbackName = null)
where T : IIntegrationEvent;
void Publish<T>(string name, T? contentObj, IDictionary<string, string?> headers)
where T : IIntegrationEvent;
Task PublishDelayAsync<T>(TimeSpan delayTime, string name, T? contentObj, IDictionary<string, string?> headers, CancellationToken cancellationToken = default)
where T : IIntegrationEvent;
Task PublishDelayAsync<T>(TimeSpan delayTime, string name, T? contentObj, string? callbackName = null, CancellationToken cancellationToken = default)
where T : IIntegrationEvent;
void PublishDelay<T>(TimeSpan delayTime, string name, T? contentObj, IDictionary<string, string?> headers)
where T : IIntegrationEvent;
void PublishDelay<T>(TimeSpan delayTime, string name, T? contentObj, string? callbackName = null)
where T : IIntegrationEvent;
}
实现EventBus
新建一个EventBus类库,来集成Cap和MediatR并实现EventBus.Abstractions。
dotnet new classlib --name EventBusDemo.EventBus
增加MediatR和Cap的包,Cap需要的具体存储和传输,可以在启动项目中配置。
<ItemGroup>
<PackageReference Include="DotNetCore.CAP" Version="7.2.0" />
<PackageReference Include="MediatR" Version="12.1.1" />
</ItemGroup>
<ItemGroup>
<ProjectReference Include="..\EventBusDemo.EventBus.Abstractions\EventBusDemo.EventBus.Abstractions.csproj" />
</ItemGroup>
实现ILocalEventBus,实则时注入MediatR,将领域事件交给MediatR处理。
using EventBusDemo.EventBus.Abstractions.Local;
using MediatR;
namespace EventBusDemo.EventBus.Local;
public class LocalEventBus : ILocalEventBUs
{
private readonly IPublisher _publisher;
public LocalEventBus(IPublisher publisher)
{
_publisher = publisher;
}
public async Task Publish(IDomainEvent domainEvent, CancellationToken cancellationToken = default)
{
await _publisher.Publish(domainEvent, cancellationToken);
}
public async Task Publish<T>(T domainEvent, CancellationToken cancellationToken = default) where T : IDomainEvent
{
await _publisher.Publish(domainEvent, cancellationToken);
}
}
实现IDistributedEventBus,也是注入Cap,将集成事件交给Cap处理。
using DotNetCore.CAP;
using EventBusDemo.EventBus.Abstractions.Distributed;
namespace EventBusDemo.EventBus.Distributed
{
public class DistributedEventBus : IDistrbutedEventBus
{
private readonly ICapPublisher _capPublisher;
public DistributedEventBus(ICapPublisher capPublisher)
{
_capPublisher = capPublisher;
}
public void Publish<T>(string name, T? contentObj, string? callbackName = null) where T : IIntegrationEvent
{
_capPublisher.Publish(name, contentObj, callbackName);
}
public void Publish<T>(string name, T? contentObj, IDictionary<string, string?> headers) where T : IIntegrationEvent
{
_capPublisher.Publish(name, contentObj, headers);
}
public async Task PublishAsync<T>(string name, T? contentObj, string? callbackName = null, CancellationToken cancellationToken = default) where T : IIntegrationEvent
{
await _capPublisher.PublishAsync(name, contentObj, callbackName, cancellationToken);
}
public async Task PublishAsync<T>(string name, T? contentObj, IDictionary<string, string?> headers, CancellationToken cancellationToken = default) where T : IIntegrationEvent
{
await _capPublisher.PublishAsync(name, contentObj, headers, cancellationToken);
}
public void PublishDelay<T>(TimeSpan delayTime, string name, T? contentObj, IDictionary<string, string?> headers) where T : IIntegrationEvent
{
_capPublisher.PublishDelay(delayTime, name, contentObj, headers);
}
public void PublishDelay<T>(TimeSpan delayTime, string name, T? contentObj, string? callbackName = null) where T : IIntegrationEvent
{
_capPublisher.PublishDelay(delayTime, name, contentObj, callbackName);
}
public async Task PublishDelayAsync<T>(TimeSpan delayTime, string name, T? contentObj, IDictionary<string, string?> headers, CancellationToken cancellationToken = default) where T : IIntegrationEvent
{
await _capPublisher.PublishDelayAsync(delayTime, name, contentObj, headers, cancellationToken);
}
public async Task PublishDelayAsync<T>(TimeSpan delayTime, string name, T? contentObj, string? callbackName = null, CancellationToken cancellationToken = default) where T : IIntegrationEvent
{
await _capPublisher.PublishDelayAsync(delayTime, name, contentObj, callbackName, cancellationToken);
}
}
}
如此一来,在Domain或是Application中使用IEventBus时,对底层具体使用的包便无感知(MediatR的服务注册和Cap的配置部分还可抽象一层来隔离)。
发布领域事件
如在DomainService中,将事件发布出去,通过观察者模式,找到对应的处理器,完成其他业务逻辑,以此来达到代码解耦。此处直接在服务中调用localEventBus使用,另外一种方案是在DbContext保存时通过SaveChange方法中来调用,这种情况需要事件先保存在某个位置,如聚合本身,后续文章在提到事务时一并扩展。
public class OrderService
{
private readonly ILocalEventBus _localEventBus;
public OrderService(ILocalEventBus localEventBus)
{
_localEventBus = localEventBus;
}
public async Task<Order> CreateOrder(string name)
{
var order = new Order()
{
Id = Guid.NewGuid(),
Name = name,
};
await _localEventBus.Publish(new OrderCreatedDomainEvent()
{
Id = order.Id,
Name = order.Name
});
return order;
}
}
发布集成事件
如在AppService中需要通过集成事件对外通知时,注入IDistributedEventBus,便可通过底层Cap将事件广播出去,由此实现发布订阅模式。此处对于事件名还可以融合到事件本身,后续文章中扩展。
public class OrderAppService
{
private readonly IDistributedEventBus _distributedEventBus;
private readonly OrderService _orderService;
public OrderAppService(
IDistributedEventBus distributedEventBus,
OrderService orderService)
{
_distributedEventBus = distributedEventBus;
_orderService = orderService;
}
public async Task<Guid> CreateOrder(string name)
{
var order = await _orderService.CreateOrder(name);
await _distributedEventBus.PublishAsync("OrderCreated", new OrderCreatedIntegrationEvent()
{
Id = order.Id,
Name = name
});
return order.Id;
}
}
标签:MediatR,Cap,name,contentObj,事件,EventBus,public,string From: https://www.cnblogs.com/CKExp/p/17664069.html2023-08-29,望技术有成后能回来看见自己的脚步