自从Wing正式发布以后，很多童鞋反馈对Saga分布式事务比较感兴趣，今天就跟大家分享一下“跨行转账”的分布式事务实践案例，入门使用教程请自行前往Wing官方文档。
假设自己名下有“中国农业银行（ABC）”和“中国工商银行（ICBC）”的账户余额各1万元，现在从“ABC”跨行转账1000元到“ICBC”。对于“ABC”我们创建一个项目名称为
“Saga.Bank.ABC”，“跨行转账”这个动作我们分为两个事务单元来处理：
1、当前账户扣减1000元，定义一个事务单元的数据传输模型（MyAccountUnitModel），一个事务单元的实现类（MyAccountSagaUnit），如果我们定义的事务策略是“向前恢复”，那就只需要实现“Commit”
方法，否则还需要实现 “Cancel”方法，代码如下：
事务单元的数据传输模型（MyAccountUnitModel）
1 using System;
2 using Wing.Saga.Client;
3
4 namespace Saga.Bank.ABC.TransferSagaUnits
5 {
6 [Serializable]
7 public class MyAccountUnitModel : UnitModel
8 {
9 /// <summary>
10 /// 账号
11 /// </summary>
12 public string BankNo { get; set; }
13
14 /// <summary>
15 /// 转出金额
16 /// </summary>
17 public double Amount { get; set; }
18 }
19 }
事务单元的实现类（MyAccountSagaUnit）
1 using Microsoft.AspNetCore.Mvc;
2 using System.Threading.Tasks;
3 using Wing.Saga.Client;
4
5 namespace Saga.Bank.ABC.TransferSagaUnits
6 {
7 /// <summary>
8 /// 当前账户操作
9 /// </summary>
10 public class MyAccountSagaUnit : SagaUnit<MyAccountUnitModel>
11 {
12 public override Task<SagaResult> Cancel(MyAccountUnitModel model, SagaResult previousResult)
13 {
14 MyAccount.Balance += model.Amount;
15 return Task.FromResult(new SagaResult());
16 }
17
18 public override Task<SagaResult> Commit(MyAccountUnitModel model, SagaResult previousResult)
19 {
20 var result = new SagaResult();
21 if (MyAccount.Balance < model.Amount)
22 {
23 result.Success = false;
24 result.Msg = "转账失败，当前账户余额不足！";
25 }
26 MyAccount.Balance -= model.Amount;
27 return Task.FromResult(result);
28 }
29 }
30 }
2、调用收款行“ICBC”的接口，同样，也是定义一个事务单元的数据传输模型（TransferOutUnitModel），一个事务单元的实现类（TransferOutSagaUnit），代码如下：
事务单元的数据传输模型（TransferOutUnitModel）
1 using System;
2 using Wing.Saga.Client;
3
4 namespace Saga.Bank.ABC.TransferSagaUnits
5 {
6 [Serializable]
7 public class TransferOutUnitModel : UnitModel
8 {
9 /// <summary>
10 /// 收款账号
11 /// </summary>
12 public string BankNo { get; set; }
13
14 /// <summary>
15 /// 收款行
16 /// </summary>
17 public string BankName { get; set; }
18
19 /// <summary>
20 /// 接收金额
21 /// </summary>
22 public double Amount { get; set; }
23 }
24 }
事务单元的实现类（TransferOutSagaUnit）
1 using System.Net.Http;
2 using System;
3 using System.Threading.Tasks;
4 using Wing;
5 using Wing.Saga.Client;
6 using Wing.ServiceProvider;
7 using Newtonsoft.Json;
8 using Wing.Result;
9 using System.Text;
10
11 namespace Saga.Bank.ABC.TransferSagaUnits
12 {
13 /// <summary>
14 /// 账户转出操作
15 /// </summary>
16 public class TransferOutSagaUnit : SagaUnit<TransferOutUnitModel>
17 {
18 private readonly IServiceFactory _serviceFactory = App.GetService<IServiceFactory>();
19 private readonly IHttpClientFactory _httpClientFactory = App.GetService<IHttpClientFactory>();
20
21 public override Task<SagaResult> Cancel(TransferOutUnitModel model, SagaResult previousResult)
22 {
23 throw new NotImplementedException();
24 }
25
26 public override Task<SagaResult> Commit(TransferOutUnitModel model, SagaResult previousResult)
27 {
28 return _serviceFactory.InvokeAsync("Saga.Bank.ICBC", async serviceAddr =>
29 {
30 var client = _httpClientFactory.CreateClient();
31 client.BaseAddress = new Uri(serviceAddr.ToString());
32 var response = await client.PostAsync("/TransferReceive", new StringContent(JsonConvert.SerializeObject(model), Encoding.UTF8, "application/json"));
33 var sagaResult = new SagaResult();
34 if (response.IsSuccessStatusCode)
35 {
36 var apiStrResult = await response.Content.ReadAsStringAsync();
37 var apiResult = JsonConvert.DeserializeObject<ApiResult<bool>>(apiStrResult);
38 if (apiResult.Code == ResultType.Success)
39 {
40 sagaResult.Success = apiResult.Data;
41 }
42 else
43 {
44 sagaResult.Success = false;
45 }
46 sagaResult.Msg = apiResult.Msg;
47 }
48 else
49 {
50 sagaResult.Success= false;
51 sagaResult.Msg = $"调用工商银行接口失败，http状态码：{(int)response.StatusCode}";
52 }
53 return sagaResult;
54 });
55 }
56 }
57 }
以上两个事务单元将组成一个完整的“跨行转账”事务，代码如下：
1 using Microsoft.AspNetCore.Mvc;
2 using Microsoft.AspNetCore.Routing;
3 using Saga.Bank.ABC.TransferSagaUnits;
4 using System;
5 using Wing.Persistence.Saga;
6 using Wing.Saga.Client;
7
8 namespace Saga.Bank.ABC.Controllers
9 {
10 /// <summary>
11 /// 转账
12 /// </summary>
13 [ApiController]
14 [Route("[controller]")]
15 public class TransferAccountsController : ControllerBase
16 {
17 public TransferAccountsController()
18 {
19 }
20
21 /// <summary>
22 /// 当前账户余额
23 /// </summary>
24 /// <returns></returns>
25 public string Get()
26 {
27 return $"我是中国农业银行账户，当前账户余额为：{MyAccount.Balance}¥";
28 }
29
30
31 [HttpGet("{amount}")]
32 public bool Get(double amount)
33 {
34 if (amount <= 0)
35 {
36 throw new Exception("转账金额必须大于0");
37 }
38 var result = Wing.Saga.Client.Saga.Start("跨行转账", new SagaOptions { TranPolicy = TranPolicy.Forward })
39 .Then(new MyAccountSagaUnit(), new MyAccountUnitModel
40 {
41 Name = "当前账户扣减",
42 BankNo = MyAccount.BankNo,
43 Amount = 1000
44 })
45 .Then(new TransferOutSagaUnit(), new TransferOutUnitModel
46 {
47 Name = "调用收款行接口",
48 BankNo = "987654321",
49 Amount = 1000,
50 BankName = "中国工商银行"
51 })
52 .End();
53 if (!result.Success)
54 {
55 throw new Exception(result.Msg);
56 }
57 return result.Success;
58 }
59 }
60 }
对于“ICBC”，我们创建一个项目名称为“Saga.Bank.ICBC”，它的职责很简单，就是增加收款账号的转账金额，代码如下：
1 using Microsoft.AspNetCore.Mvc;
2 using Saga.Bank.ICBC.Models;
3 using System;
4
5 namespace Saga.Bank.ICBC.Controllers
6 {
7 /// <summary>
8 /// 转账
9 /// </summary>
10 [ApiController]
11 [Route("[controller]")]
12 public class TransferReceiveController : ControllerBase
13 {
14 private static bool _result = false;
15 public TransferReceiveController()
16 {
17 }
18
19 /// <summary>
20 /// 当前账户余额
21 /// </summary>
22 /// <returns></returns>
23 public string Get()
24 {
25 return $"我是中国工商银行账户，当前账户余额为：{MyAccount.Balance}¥";
26 }
27
28 /// <summary>
29 /// 手动控制跨行转账收款是否成功，测试需要
30 /// </summary>
31 /// <param name="result"></param>
32 /// <returns></returns>\
33 [HttpGet("{result}")]
34 public bool Get(int result)
35 {
36 _result = result == 1;
37 return _result;
38 }
39
40 /// <summary>
41 /// 跨行转账收款动作
42 /// </summary>
43 /// <param name="model"></param>
44 /// <returns></returns>
45 /// <exception cref="Exception"></exception>
46 [HttpPost]
47 public bool Post(ReceivedModel model)
48 {
49 if (model.BankNo != MyAccount.BankNo)
50 {
51 throw new Exception("账号不存在！");
52 }
53 if (!_result)
54 {
55 throw new Exception("跨行转账业务失败！");
56 }
57 MyAccount.Balance += model.Amount;
58 return true;
59 }
60 }
61 }
启动“Saga.Bank.ICBC”项目，可以看到当前账户余额为10000元，如下图：
启动“Saga.Bank.ABC”项目，可以看到当前账户余额也是为10000元，如下图：
启动Saga协调服务“Saga.Bank.Server”，启动“Wing.UI”示例1.3， 我们调用农业银行跨行转账接口 http://localhost:9110/TransferAccounts/1000，这时我们可以看到“ABC”的余额为
9000元，“ICBC”的余额还是10000元，因为“ICBC”自身业务操作处理失败，如下图所示：
我们把“Saga.Bank.ICBC”的收款接口处理结果改为“成功”（调用接口 http://localhost:9111/TransferReceive/1），1分钟左右，我们重新查看“ICBC”的账户余额为11000元，“跨行转账”事务也处理完成了，如下图：
代码完整示例下载地址：https://gitee.com/linguicheng/wing-demo