---
title: '[.NET] 流程引擎 Workflow Core 的碰壁過程'
---
## Workflow Core 簡介
Workflow Core 是一個基於 .NET 的輕量級工作流程引擎，用於建構長期執行的工作流程與業務邏輯，支援分散式系統、事件驅動以及持久化， 可用電子商務訂單處理、自動化任務或複雜事件調度等等工作流程。

特點
* 跨平台：可使用 .NET 進行開發，並且與 .NET 8 兼容
* 事件驅動：支援事件等待，事件觸發後繼續執行流程
* 持久化：支援　PostgreSQL、SQL Server、Redis，來儲存 Workflow 的流程和狀態

## TL;DR
* Workflow Core 為輕量版引擎套件，適用於簡單的流程作業
* 不支援 BPMN 2.0 協議，不利於引擎套件的更換
* 可將流程產出 Json 格式，但支援的可視化工具有限
* 官方文件的範例說明不夠齊全，需以原始碼輔助

## 版本資訊
:::info
* .NET 8
* Workflow Core Version 3.13.0
:::
## 開始使用

### 基本範例
先以 Console 專案來實際操作 Workflow Core 的使用，建立好 Console 專案後輸入以下指令安裝 Workflow Core。

* 套件安裝

dotnet add package Microsoft.Extensions.DependencyInjection
dotnet add package Microsoft.Extensions.Logging
dotnet add package WorkflowCore

* 情境模擬


以下開始說明程式，拆分成主程式以及各步驟的類別實作，原始碼請參考[這裡](https://dev.azure.com/jjaywang1121/Example.Code/_git/Workflow.Core.ConsoleApp)

* Program.cs

using Microsoft.Extensions.DependencyInjection;
using WorkflowCore.Interface;
using WorkflowCore.Models;

var serviceProvider = new ServiceCollection()
  .AddLogging()
  .AddWorkflow()
  .BuildServiceProvider();

var host = serviceProvider.GetService<IWorkflowHost>();
if (host == null) throw new Exception("Fail");

host.RegisterWorkflow<ShipmentWorkflow, ShipmentData>();
host.Start();

Console.Write("輸入數量：");
var quantity = Console.ReadLine();
if (quantity == null || !int.TryParse(quantity, out int parseQuantity))
{
  throw new Exception("Fail");
}

var shipData = new ShipmentData();
shipData.Id = Guid.NewGuid();
shipData.Quantity = parseQuantity;

await host.StartWorkflow("ShipmentWorkflow", shipData);

Console.ReadLine();
host.Stop();

* 工作流類別 ShipmentWorkflow.cs

public class ShipmentWorkflow : IWorkflow<ShipmentData>
{
  public string Id => "ShipmentWorkflow";
  public int Version => 1;

  public void Build(IWorkflowBuilder<ShipmentData> builder)
  {
    builder.StartWith<CheckInventory>()
    .Input(step => step.Quantity, data => data.Quantity)
    .Output(data => data.IsInventorySufficient, step => step.IsInventorySufficient)
    .If(data => data.IsInventorySufficient).Do(
        builder => builder
        .If(data => data.Quantity > 100).Do(
            builder => builder.StartWith<SupervisorApproval>()
            .Output(data => data.IsApproved, step => step.IsApproved)
            .If(data => data.IsApproved).Do(
                builder => builder.StartWith<ShipItems>()
                .Input(step => step.Quantity, data => data.Quantity)
            )
        )
        .If(data => data.Quantity <= 100).Do(
            builder => builder.StartWith<ShipItems>()
            .Input(step => step.Quantity, data => data.Quantity)
        )
    )
    .Then(ctx => Console.WriteLine("流程結束"))
    .EndWorkflow();
}

* 官方文件連結
:::success
* [Inputs and Outputs](https://workflow-core.readthedocs.io/en/latest/json-yaml/#inputs-and-outputs)
* [If Conditions](https://workflow-core.readthedocs.io/en/latest/control-structures/#if-conditions)
:::

* 檢查庫存 CheckInventory.cs

public class CheckInventory : StepBody
{
  public int Quantity { get; set; }
  public bool IsInventorySufficient { get; set; }

  public override ExecutionResult Run(IStepExecutionContext context)
  {
    Console.WriteLine($"檢查庫存: {Quantity}");
    IsInventorySufficient = Quantity <= 200;
    if (!IsInventorySufficient) Console.WriteLine("庫存不足");
    return ExecutionResult.Next();
  }
}

* 主管簽核 SupervisorApproval.cs

public class SupervisorApproval : StepBody
{
  public bool IsApproved { get; set; }

  public override ExecutionResult Run(IStepExecutionContext context)
  {
    Console.WriteLine("等待主管簽核中...");

    IsApproved = true;
    var output = IsApproved ? "通過" : "不通過";
    Console.WriteLine($"主管簽核：{output}");

    return ExecutionResult.Next();
  }
}

* 出貨 ShipItems.cs

public class ShipItems : StepBody
{
  public int Quantity { get; set; }

  public override ExecutionResult Run(IStepExecutionContext context)
  {
    Console.WriteLine($"確定出貨，數量：{Quantity}");
    return ExecutionResult.Next();
  }
}

### 搭配 WebAPI 專案
開放 WebAPI 給外部程式做存取，以及開啟持久化設定，可以支援外部事件的觸發，範例將實現以下功能，原始碼請參考[這裡](https://dev.azure.com/jjaywang1121/Example.Code/_git/Workflow.Core.WebAPI)
:::info
* Store workflow in postgres.
* Start or suspend workflow.
* Event trigger in workflow.
* Get specific workflow information.
:::

* Program.cs

// 開啟持久化設定
// UsePostgreSQL(string connectionString, bool canCreateDB, bool canMigrateDB, [string schemaName = "wfc"])
builder.Services.AddWorkflow(x => x.UsePostgreSQL("<connectionstring>", true, true));

// 中間省略...

var host = app.Services.GetService<IWorkflowHost>() ?? throw new Exception("fail");

host.RegisterWorkflow<ShipmentWorkflow, ShipmentData>();
host.Start();

app.Lifetime.ApplicationStopped.Register(() => host.Stop());

app.Run();

SupervisorApproval.cs 特別提出簽核流程 API 的處理過程，需要使用 `ExecutionResult.WaitForEvent` 來等待簽核事件的觸發，並且需要開啟持久化設定

> [!Note] 補充說明
> 需要開啟持久化設定的原因為工作流程的狀態預設是存在記憶體中，當程式結束後工作狀態會跟著消失。

* SupervisorApproval.cs

public class SupervisorApproval : StepBody
{
    public bool IsApproved { get; set; }

    public override ExecutionResult Run(IStepExecutionContext context)
    {
        if (!context.ExecutionPointer.EventPublished)
        {
            Console.WriteLine("等待主管簽核中...");
            return ExecutionResult.WaitForEvent("Approve", context.Workflow.Id, DateTime.Now);
        }

        IsApproved = (bool)context.ExecutionPointer.EventData;
        var output = IsApproved ? "通過" : "不通過";
        Console.WriteLine($"主管簽核：{output}");
        return ExecutionResult.Next();
    }
}

> [!Warning] 踩雷
從原始碼 [WaitFor](https://github.com/danielgerlag/workflow-core/blob/3112482d403226de04caebd27c66842cdca178ec/src/WorkflowCore/Primitives/WaitFor.cs#L7) 中可以看到如果執行流程中有事件觸發的等待，必須去判斷事件 `context.ExecutionPointer.EventPublished` 是否已經觸發

* 觸發簽核事件

[HttpPost("[action]")]
public async Task<IActionResult> Approve(ApproveData approveData)
{
    await _workflowHost.PublishEvent("Approve", approveData.WorkflowId, approveData.Approve, DateTime.Now);
    return Ok("OK");
}

/// <summary>
/// PublishEvent
/// </summary>
/// <param name="eventName"></param>
/// <param name="eventKey"></param>
/// <param name="eventData"></param>
/// <param name="effectiveDate"></param>
/// <returns></returns>
Task PublishEvent(string eventName, string eventKey, object eventData, DateTime? effectiveDate = null);

## 參考資料
* [官方文件](https://workflow-core.readthedocs.io/en/latest/)
* [原始碼](https://github.com/danielgerlag/workflow-core)

## 延伸閱讀
* [Elsa Workflows](https://v3.elsaworkflows.io/)
* [SpiffWorkflow ](https://www.spiffworkflow.org/)
* [WorkflowEngine.NET](https://github.com/optimajet/WorkflowEngine.NET)