前言

CAP用来处理分布式事务以及提供EventBus的功能，具有轻量级，高性能，易使用等特点。

安装包

Install-package DotNetCore.CAP   
Install-package DotNetCore.CAP.RabbitMQ  
Install-package DotNetCore.CAP.SqlServer   

使用方法

配置

Startup->ConfigureServices中添加服务:

//add CAP  
services.AddCap(x =>  
{  
    x.UseEntityFramework<OrderContext>(); // 使用EF  

    x.UseSqlServer(connecttext); // 使用SQL Server  

    x.UseRabbitMQ(cfg =>  
    {  
        cfg.HostName = "127.0.0.1";  
        cfg.Port = 5672;  
        cfg.UserName = "test1";  
        cfg.Password = "test1";  
    }); // 使用RabbitMQ  

    x.UseDashboard(); // Dashboard  

    // Below settings is just for demo  
    x.FailedRetryCount = 2;  
    x.FailedRetryInterval = 5;  
});  

案例

模仿订单系统下单成功后，推送后续消息到各个子系统，保证分布式系统间通信的一致性。

代码

订单系统的消息发布者:

public interface IOrderRepository
{  
    bool CreateOrder(Order order);  
}  

public class OrderRepository : IOrderRepository  
{  
    public readonly OrderContext _context; //ef 订单上下文  
    public readonly ICapPublisher _capPublisher;//cap 消息发布者  

    public OrderRepository(OrderContext context, ICapPublisher capPublisher)  
    {  
        this._context = context;  
        this._capPublisher = capPublisher;  
    }  

    public bool CreateOrder(Order order)  
    {  
        using (var trans = _context.Database.BeginTransaction())  
        {  
            var orderEntity = new Order()  
            {  
                OrderTime = order.OrderTime  
            };  

            _context.Orders.Add(orderEntity);  
            _context.SaveChanges();  

            _capPublisher.Publish("czhsoft.services.order.create", orderEntity);  

            trans.Commit();  
        }  

        return true;  
    }  
}  

其它子系统的消息订阅者：

public interface IOrderSubscriberService  
{  
    void ConsumeOrderMessage(Order message);  
}  

public class OrderSubscriberService : IOrderSubscriberService, ICapSubscribe  
{  
    public OrderSubscriberService()  
    {  
    }  

    [CapSubscribe("czhsoft.services.order.create")]  
    public void ConsumeOrderMessage(Order message)  
    {  
        Console.Out.WriteLine($"[MsgApi] Received message : order id {message.OrderId}");  
    }  
}