微服务简单实现最终一致性

Python微信订餐小程序课程视频

https://edu.youkuaiyun.com/course/detail/36074

Python实战量化交易理财系统

https://edu.youkuaiyun.com/course/detail/35475
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。

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| 12345678910111213 | // POST api/``[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：

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| 12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758 | 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(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;``}``}``} |

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| 12345678910111213141516171819202122232425262728293031323334353637383940414243 | 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(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 header)
 {
 if (message.Contains("Product"))
 {
 var product = JsonConvert.DeserializeObject(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(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。

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| 123456789101112 | [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：

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| 12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849 | 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``{``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 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(``"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)