[.NET项目实战] Elsa开源工作流组件应用（三）：实战演练

补充

之前的文章简单介绍了工作流和Elsa工作流库，这里再补充说明两点

工作流的使用场景非常广泛，几乎涵盖了所有需要进行业务流程自动化管理的领域。
学习一个开源库，最简单的方法就是看源码，Elsa的工作流引擎源码非常简单易懂，并且提供了非常丰富的示例代码，举一个例子：审批工作流示例.\src\samples\aspnet\Elsa.Samples.AspNet.DocumentApproval

在这里插入图片描述

这个审批流是这样的：
作者发来一个文章，有两个审批人需要全部审批通过，文章才算通过，否则退回。

我们尝试阅读工作流源代码DocumentApprovalWorkflow.cs，并运行此项目，用postman发送请求

第一步：

假设这名叫Amanda的作者要发布文章，请求发送后，作者浏览器显示发送成功稍安勿躁之类的提示

同时后台打印作者信息和4个链接，分别是Jack和Lucy两位审批人“通过”和“退回”的url链接

Activities =
{
    new HttpEndpoint
    {
        Path = new("/documents"),
        SupportedMethods = new(new[] { HttpMethods.Post }),
        ParsedContent = new(documentVariable),
        CanStartWorkflow = true
    },
    new WriteLine(context => $"Document received from {documentVariable.Get<dynamic>(context)!.Author.Name}."),
    new WriteHttpResponse
    {
        Content = new("<h1>Request for Approval Sent</h1><p>Your document has been received and will be reviewed shortly.</p>"),
        ContentType = new(MediaTypeNames.Text.Html),
        StatusCode = new(HttpStatusCode.OK),
        ResponseHeaders = new(new HttpHeaders { ["X-Powered-By"] = new[] { "Elsa 3.0" } })
    },

第二步：

Jack觉得文章不错，通过浏览器请求了“通过”链接，而Lucy觉得文章还不够好，需改进，她在浏览器中请求了“退回”链接。

两位审批人的审批结果存储于approvedVariable变量中

同时他们的浏览器返回的响应内容：Thanks for the approval 或 Sorry to hear that

    new Fork
    {
        JoinMode = ForkJoinMode.WaitAll,
        Branches =
        {
            // Jack
            new Sequence
            {
                Activities =
                {
                    new WriteLine(context => $"Jack approve url: \n {GenerateSignalUrl(context, "Approve:Jack")}"),
                    new WriteLine(context => $"Jack reject url: \n {GenerateSignalUrl(context, "Reject:Jack")}"),
                    new Fork
                    {
                        JoinMode = ForkJoinMode.WaitAny,
                        Branches =
                        {
                            // Approve
                            new Sequence
                            {
                                Activities =
                                {
                                    new Event("Approve:Jack"),
                                    new SetVariable
                                    {
                                        Variable = approvedVariable,
                                        Value = new(true)
                                    },
                                    new WriteHttpResponse
                                    {
                                        Content = new("Thanks for the approval, Jack!"),
                                    }
                                }
                            },

                            // Reject
                            new Sequence
                            {
                                Activities =
                                {
                                    new Event("Reject:Jack"),
                                    new SetVariable
                                    {
                                        Variable = approvedVariable,
                                        Value = new(false)
                                    },
                                    new WriteHttpResponse
                                    {
                                        Content = new("Sorry to hear that, Jack!"),
                                    }
                                }
                            }
                        }
                    }
                }
            },

            // Lucy
            new Sequence
            {
                Activities =
                {
                    new WriteLine(context => $"Lucy approve url: \n {GenerateSignalUrl(context, "Approve:Lucy")}"),
                    new WriteLine(context => $"Lucy reject url: \n {GenerateSignalUrl(context, "Reject:Lucy")}"),
                    new Fork
                    {
                        JoinMode = ForkJoinMode.WaitAny,
                        Branches =
                        {
                            // Approve
                            new Sequence
                            {
                                Activities =
                                {
                                    new Event("Approve:Lucy"),
                                    new SetVariable
                                    {
                                        Variable = approvedVariable,
                                        Value = new(true)
                                    },
                                    new WriteHttpResponse
                                    {
                                        Content = new("Thanks for the approval, Lucy!"),
                                    }
                                }
                            },

                            // Reject
                            new Sequence
                            {
                                Activities =
                                {
                                    new Event("Reject:Lucy"),
                                    new SetVariable
                                    {
                                        Variable = approvedVariable,
                                        Value = new(false)
                                    },
                                    new WriteHttpResponse
                                    {
                                        Content = new("Sorry to hear that, Lucy!"),
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    },

第三步：

根据approvedVariable变量判定文章是否被审核通过。

如果通过则在控制台打印Document document-1 approved!, 否则打印Document document-1 not rejected!

    new WriteLine(context => $"Approved: {approvedVariable.Get<bool>(context)}"),
    new If(context => approvedVariable.Get<bool>(context))
    {
        Then = new WriteLine(context => $"Document ${documentVariable.Get<dynamic>(context)!.Id} approved!"),
        Else = new WriteLine(context => $"Document ${documentVariable.Get<dynamic>(context)!.Id} rejected!")
    }
}

Elsa工作流源码还提供了大量的Sample，这里就不一一列举了，

需求描述

根据不同的时间规则，发送下发问卷给客户填写。

下发问卷给用户填写，且填写有超时时间，期间要提醒用户答题，

如果问卷未在规定的时间内作答则，则作废，并提醒用户。

需求分析

我们将需求尽可能分解成为单一职责的功能单元，并定义这些功能单元的输入输出。

下发问卷任务 PublishQuestionnaireActivity

下发问卷是将问卷（Questionnaire）实例化成问卷实例（Survey），问卷实例绑定用户Id，用户在问卷实例上作答。明确输入和输出：

输入：问卷ID
输出：问卷实例对象SurveyDto

通知任务 NotificationActivity

通知在这个需求中需要发送问卷状态，时间等内容给对应的用户，同通至少包含标题和内容。

输入：标题和内容
输出：无

问卷状态跟踪任务 WaitFillInSurveyActivity

这个任务要追踪问卷实例的状态，当问卷实例状态为已完成时，可以继续执行后续任务。

输入：问卷实例ID
输出：无

定时和延时任务

用于延时执行每个下发问卷的时间，等待问卷超时，以及延时发送通知等。

输入：开始日期，延时日期，间隔时间或cron表达式
输出：无

根任务

根任务包含所有的子任务，完成这个任务后，整个流程结束。在这个需求中根任务只需要知道将什么问卷，发送给哪位用户，以及在何时发送这三个问题。

输入：问卷ID，用户ID，发送时间
输出：无

各子任务参数对于他们的根任务是透明的（Invisible），根任务只需要关心是否完成，而不需要知道任务参数。

代码实现

下发问卷任务可以抽象成为下发问卷活动 PublishQuestionnaireActivity
创建PublishQuestionnaireActivity类并设置输入QuestionnaireId，输出SurveyDto

public class PublishQuestionnaireActivity : Activity<SurveyDto>
{
    public PublishQuestionnaireActivity()
    {

    }
    public PublishQuestionnaireActivity(long questionnaireId)
    {
        QuestionnaireId = new Input<long>(questionnaireId);
    }


    
    public Input<long> QuestionnaireId { get; set; } = default!;
}

重写ExecuteAsync方法，完成问卷下发逻辑

protected override async ValueTask ExecuteAsync(ActivityExecutionContext context)
{
    var _surveyAppService = context.GetRequiredService<ISurveyAppService>();
    if (_surveyAppService != null)
    {
        var currentUserId = await context.GetInputValueAsync<Guid>("UserId");
        var survey = await _surveyAppService.PublishAsync(new PublishInput()
        {
            QuestionnaireId = this.QuestionnaireId.Get<long>(context),
            UserId = currentUserId

        }) ?? throw new Exception("创建问卷失败");
        context.SetResult(survey);
    }


    await context.CompleteActivityAsync();

}

如此，其他的任务分别抽象成为相应的活动，这里展示完整代码

通知活动：NotificationActivity

public class NotificationActivity : Activity
{


    public NotificationActivity()
    {

    }
    public NotificationActivity(string title, string content)
    {
        Content = new Input<string>(content);
        Title = new Input<string>(title);
    }

    protected override async ValueTask ExecuteAsync(ActivityExecutionContext context)
    {
        var notificationManager = context.GetRequiredService<NotificationManager>();

        if (notificationManager != null)
        {
            var title = this.Title.Get(context);
            var content = this.Content.Get(context);
            var currentUserId = await context.GetInputValueAsync<Guid>("UserId");
            var data = new CreatePrivateMessageNotificationEto(currentUserId, title, content);
            await notificationManager.Send(data);
        }


    await context.CompleteActivityAsync();

}

    public Input<string> Title { get; set; } = default!;
    public Input<string> Content { get; set; } = default!;
}

等待问卷完成活动：WaitFillInSurveyActivity

public class WaitFillInSurveyActivity : Activity
{
    public WaitFillInSurveyActivity()
    {

    }
    public WaitFillInSurveyActivity(Func<ExpressionExecutionContext, long?> surveyId)
: this(Expression.DelegateExpression(surveyId))
    {
    }

    public WaitFillInSurveyActivity(long surveyId) => SurveyId = new Input<long>(surveyId);

    public WaitFillInSurveyActivity(Expression expression) => SurveyId = new Input<long>(expression, new MemoryBlockReference());


    /// <inheritdoc />
    protected override ValueTask ExecuteAsync(ActivityExecutionContext context)
    {
        var surveyId = SurveyId.Get(context);
        if (surveyId == default)
        {
            var survey = context.ExpressionExecutionContext.GetLastResult<SurveyDto>();
            surveyId = survey.Id;
        }
        var payload = new WaitFillInSurveyBookmarkPayload(surveyId);
        context.CreateBookmark(new CreateBookmarkArgs
        {
            Payload = payload,
            Callback = Resume,
            BookmarkName = Type,
            IncludeActivityInstanceId = false
        });
        return ValueTask.CompletedTask;
    }

    private async ValueTask Resume(ActivityExecutionContext context)
    {
        await context.CompleteActivityAsync();
    }

    public Input<long> SurveyId { get; set; } = default!;
}

此任务需要等待，我们创建一个Bookmark，注意创建Bookmark时，我们根据问卷实例SurveyId判断是否完成问卷的回答，因此指定IncludeActivityInstanceId为false，创建携带SurveyId的Payload类型：

public record WaitFillInSurveyBookmarkPayload(long SurveyId);

在回调OnResumeAsync中，我们使用context.CompleteActivityAsync来完成任务。

public QuestionnaireActivity(long questionnaireId, TimeSpan fillInTimeout)
{
    this.QuestionnaireId = questionnaireId;
    this.FillInTimeout = fillInTimeout;
    var currentSurvey = new Variable<SurveyDto>();
    Variables.Add(currentSurvey);
    Activities = new List<IActivity>()
    {
        new WriteLine("Start"),

        new PublishQuestionnaireActivity(QuestionnaireId)
        {
            Name="PublishQuestionnaire",
            Result=new Output<Questionnaire.Survey.Dto.SurveyDto> (currentSurvey)
        },
        new NotificationActivity("新问卷提醒", "您有新的问卷，请查收"),

        new Fork
        {
            JoinMode = ForkJoinMode.WaitAny,
            Branches =
            {
                new Sequence
                {
                    Activities =
                    {
                        new Delay
                        {
                            Id = "RemindDelay",
                            TimeSpan = new(RemindDelay)
                        },
                        new NotificationActivity("问卷即将超时", "问卷即将超时，请尽快回答")
                    }
                },

                new Sequence
                {
                    Activities =
                    {
                        new WriteLine("问卷计时器开始"),
                        new Delay
                        {
                            Id = "TimeoutDelay",
                            TimeSpan = new(FillInTimeout)
                        },

                        new NotificationActivity("问卷已过期", "问卷已过期，请等待工作人员处理"),

                        // This should break the while loop, not matter how high up in the tree it is.
                        new Fault()
                        {
                            Message=new ("问卷回答超时")
                        }
                    }
                },
                new Sequence
                {
                    Activities =
                    {
                        new WriteLine("开始等待问卷提交信号"),
                        new WaitFillInSurveyActivity(context => currentSurvey.Get<SurveyDto>(context)?.Id)

                    }
                }
            }
        },
        new WriteLine("完成问卷流程"),
        new Finish(),
    };
}