微服务简单实现最终一致性

有花时间去研究masstransit的saga，英文水平不过关，始终无法实现上手他的代码编排的业务，遗憾。

本文通过rabbit和sqlserver实现下单，更新库存，更新产品，模拟数据最终一致性。

 

项目结构如下,reportService可有可无，这里就相当一个链条，只要两节走通了后面可以接龙，本文有用到不省略。流程：orderservice=>eComm=>reportservice 。

 

下面先看看order的配置，通过控制器新增订单同时发布订单信息到order_exchange交换机，Key是"order.created,这样就把订单推送到了队列，等到库存服务获取订单去更新库存。

  // POST api/<OrderController>        [HttpPost]        public async Task Post([FromBody] OrderDetail orderDetail)        {            var id = await orderCreator.Create(orderDetail);            publisher.Publish(JsonConvert.SerializeObject(new OrderRequest {                 OrderId = id,                ProductId = orderDetail.ProductId,                Quantity = orderDetail.Quantity            }), "order.created", null);        }　

更新库存的代码，然后再发送消息告诉order服务，这里有哪个try包裹，如果这里有失败会触发catch，发送减库存失败的消息。order服务消费到这条消息就会执行相应的删除订单操作。代码如下：

using Ecomm.DataAccess;using Ecomm.Models;using Microsoft.Extensions.Hosting;using Newtonsoft.Json;using Plain.RabbitMQ;using System;using System.Collections.Generic;using System.Linq;using System.Threading;using System.Threading.Tasks;namespace Ecomm{    public class OrderCreatedListener : IHostedService    {        private readonly IPublisher publisher;        private readonly ISubscriber subscriber;        private readonly IInventoryUpdator inventoryUpdator;        public OrderCreatedListener(IPublisher publisher, ISubscriber subscriber, IInventoryUpdator inventoryUpdator)        {            this.publisher = publisher;            this.subscriber = subscriber;            this.inventoryUpdator = inventoryUpdator;        }        public Task StartAsync(CancellationToken cancellationToken)        {            subscriber.Subscribe(Subscribe);            return Task.CompletedTask;        }        private bool Subscribe(string message, IDictionary<string, object> header)        {            var response = JsonConvert.DeserializeObject<OrderRequest>(message);            try            {                inventoryUpdator.Update(response.ProductId, response.Quantity).GetAwaiter().GetResult();                publisher.Publish(JsonConvert.SerializeObject(                    new InventoryResponse { OrderId = response.OrderId, IsSuccess = true }                    ), "inventory.response", null);            }            catch (Exception)            {                publisher.Publish(JsonConvert.SerializeObject(                    new InventoryResponse { OrderId = response.OrderId, IsSuccess = false }                    ), "inventory.response", null);            }            return true;        }        public Task StopAsync(CancellationToken cancellationToken)        {            return Task.CompletedTask;        }    }}

　　

using Ecomm.Models;using Microsoft.Extensions.Hosting;using Newtonsoft.Json;using Plain.RabbitMQ;using System.Collections.Generic;using System.Threading;using System.Threading.Tasks;namespace OrderService{    public class InventoryResponseListener : IHostedService    {        private readonly ISubscriber subscriber;        private readonly IOrderDeletor orderDeletor;        public InventoryResponseListener(ISubscriber subscriber, IOrderDeletor orderDeletor)        {            this.subscriber = subscriber;            this.orderDeletor = orderDeletor;        }        public Task StartAsync(CancellationToken cancellationToken)        {            subscriber.Subscribe(Subscribe);            return Task.CompletedTask;        }        private bool Subscribe(string message, IDictionary<string, object> header)        {            var response = JsonConvert.DeserializeObject<InventoryResponse>(message);            if (!response.IsSuccess)            {                orderDeletor.Delete(response.OrderId).GetAwaiter().GetResult();            }            return true;        }         public Task StopAsync(CancellationToken cancellationToken)        {            return Task.CompletedTask;        }    }}

　　上面的代码是整个服务的核心业务，也很简单就是队列相互通信相互确认操作是否顺利，失败就执行回归操作，而这里我们都会写好对应补偿代码：

using Dapper;using System;using System.Collections.Generic;using System.Data.SqlClient;using System.Linq;using System.Threading.Tasks;namespace OrderService{    public class OrderDeletor : IOrderDeletor    {        private readonly string connectionString;        public OrderDeletor(string connectionString)        {            this.connectionString = connectionString;        }        public async Task Delete(int orderId)        {            using var connection = new SqlConnection(connectionString);            connection.Open();            using var transaction = connection.BeginTransaction();            try            {                await connection.ExecuteAsync("DELETE FROM OrderDetail WHERE OrderId = @orderId", new { orderId }, transaction: transaction);                await connection.ExecuteAsync("DELETE FROM [Order] WHERE Id = @orderId", new { orderId }, transaction: transaction);                transaction.Commit();            }            catch            {                transaction.Rollback();            }        }    }}

库存服务里有发布产品的接口，这里没有做过多的处理，只是把产品新增放到队列，供后面的ReportService服务获取，该服务拿到后会执行产品数量扣除：

using Microsoft.Extensions.Hosting;using Newtonsoft.Json;using Plain.RabbitMQ;using System.Collections.Generic;using System.Linq;using System.Threading;using System.Threading.Tasks;namespace ReportService{    public class ReportDataCollector : IHostedService    {        private const int DEFAULT_QUANTITY = 100;        private readonly ISubscriber subscriber;        private readonly IMemoryReportStorage memoryReportStorage;        public ReportDataCollector(ISubscriber subscriber, IMemoryReportStorage memoryReportStorage)        {            this.subscriber = subscriber;            this.memoryReportStorage = memoryReportStorage;        }        public Task StartAsync(CancellationToken cancellationToken)        {            subscriber.Subscribe(Subscribe);            return Task.CompletedTask;        }        private bool Subscribe(string message, IDictionary<string, object> header)        //private bool ProcessMessage(string message, IDictionary<string, object> header)        {            if (message.Contains("Product"))            {                var product = JsonConvert.DeserializeObject<Product>(message);                if (memoryReportStorage.Get().Any(r => r.ProductName == product.ProductName))                {                    return true;                }                else                {                    memoryReportStorage.Add(new Report                    {                        ProductName = product.ProductName,                        Count = DEFAULT_QUANTITY                    });                }            }            else            {                var order = JsonConvert.DeserializeObject<Order>(message);                if(memoryReportStorage.Get().Any(r => r.ProductName == order.Name))                {                    memoryReportStorage.Get().First(r => r.ProductName == order.Name).Count -= order.Quantity;                }                else                {                    memoryReportStorage.Add(new Report                    {                        ProductName = order.Name,                        Count = DEFAULT_QUANTITY - order.Quantity                    });                }            }            return true;        }        public Task StopAsync(CancellationToken cancellationToken)        {            return Task.CompletedTask;        }    }}

到这里整个流程大概如此。只要理清楚了订单和库存更新这里的业务，后面差不多一样，可以无限递归。代码文末有链接供下载。

这里有一个地方的代码如下,新增库存的时候同时发布消息。假如新增完订单后面崩掉了，这里是个原子操作最佳。

        [HttpPost]        public async Task Post([FromBody] OrderDetail orderDetail)        {            var id = await orderCreator.Create(orderDetail);            publisher.Publish(JsonConvert.SerializeObject(new OrderRequest {                 OrderId = id,                ProductId = orderDetail.ProductId,                Quantity = orderDetail.Quantity            }), "order.created", null);        }

　　很遗憾masstransit的saga还没有整明白，那就上cap，完成业务一致性。加了点cap代码因为之前是dapper，所以加了dbcontext和cap相关代码有点小乱。核心代码如下：

 

using DotNetCore.CAP;using MediatR;using OrderService.Command;using System.Threading;using Ecomm.Models;using System.Collections.Generic;namespace OrderService.Handler{    public class InsertOrderDetailHandler : IRequestHandler<InsertOrderDetailCommand, InsertOrderDetailModel>    {        private readonly OrderDbContext context;        private readonly ICapPublisher cap;        public InsertOrderDetailHandler(OrderDbContext context, ICapPublisher cap)        {            this.context = context;            this.cap = cap;        }        public async System.Threading.Tasks.Task<InsertOrderDetailModel> Handle(InsertOrderDetailCommand request, CancellationToken cancellationToken)        {            using(var trans =context.Database.BeginTransaction(cap))            {                var order =  context.Orders.Add(new Order                {                    UpdatedTime = System.DateTime.Today,                    UserId = request.UserId,                    UserName = request.UserName                });                var orderDetail = context.OrderDetails.Add(new OrderDetail                {                    OrderId = order.Entity.Id,                    ProductId = request.ProductId,                    Quantity = request.Quantity,                    ProductName = request.ProductName,                });                 context.SaveChanges();                                cap.Publish<OrderRequest>("order.created", new OrderRequest                {                    OrderId = order.Entity.Id,                    ProductId = orderDetail.Entity.ProductId,                    Quantity = orderDetail.Entity.Quantity                }, new Dictionary<string,string>()) ;                 trans.Commit();                return new InsertOrderDetailModel { OrderDetailid = orderDetail.Entity.Id, OrderId = order.Entity.Id, Success = true };            }        }    }}

　到这里差不多要结束了，这里的代码都可以调试运行的。因为加了cap，order服务有两套rabbitmq的配置，有冗余，而且有点坑。调试的时候注意，Plain.RabbitMQ支持的交换机不是持久化的，而cap是持久化的，所以有点不兼容。第一次运行可以先确保Plain.RabbitMQ正常，再删掉交换机，cap跑起来了再建持久化交换机，这样cap消息就会被rabbitmq接收，后面就会被库存服务消费。因为我这里cap不会自动绑定队列，Plain.RabbitMQ是可以的。所以需要新建交换机后再绑定队列。而且这里队列以Plain.RabbitMQ生成的名字来绑定。要不然又可能会调试踩坑无法出坑。 用cap不注意你连消息队列都看不到，看到了队列也看不到消费数据，这点不知道是我不会还是cap有什么难的配置。结束。。。

上例项目demo:

liuzhixin405/SimpleOrders_Next (github.com)

超简单微服务demo

liuzhixin405/SimpleOrders (github.com)