sagas.md

Saga transaction with compensation

A Saga allows you to encapsulate a sequence of steps within a saga transaction and specify compensation steps for each.

In the sample, Task2 will throw an exception, then UndoTask2 and UndoTask1 will be triggered.

builder
    .StartWith(context => Console.WriteLine("Begin"))
    .Saga(saga => saga
        .StartWith<Task1>()
            .CompensateWith<UndoTask1>()
        .Then<Task2>()
            .CompensateWith<UndoTask2>()
        .Then<Task3>()
            .CompensateWith<UndoTask3>()
    )
        .CompensateWith<CleanUp>()
    .Then(context => Console.WriteLine("End"));

Retry policy for failed saga transaction

This particular example will retry the saga every 5 seconds, but you could also simply fail completely, and process a master compensation task for the whole saga.

builder
    .StartWith(context => Console.WriteLine("Begin"))
    .Saga(saga => saga
        .StartWith<Task1>()
            .CompensateWith<UndoTask1>()
        .Then<Task2>()
            .CompensateWith<UndoTask2>()
        .Then<Task3>()
            .CompensateWith<UndoTask3>()
    )
    .OnError(Models.WorkflowErrorHandling.Retry, TimeSpan.FromSeconds(5))
    .Then(context => Console.WriteLine("End"));

Compensate entire saga transaction

You could also only specify a master compensation step, as follows

builder
    .StartWith(context => Console.WriteLine("Begin"))
        .Saga(saga => saga
            .StartWith<Task1>()
            .Then<Task2>()
            .Then<Task3>()
    )
        .CompensateWith<UndoEverything>()
    .Then(context => Console.WriteLine("End"));

Passing parameters to compensation steps

Parameters can be passed to a compensation step as follows

builder
    .StartWith<SayHello>()
        .CompensateWith<PrintMessage>(compensate => 
        {
            compensate.Input(step => step.Message, data => "undoing...");
        })

Expressing a saga in JSON or YAML

A saga transaction can be expressed in JSON or YAML, by using the WorkflowCore.Primitives.Sequence step and setting the Saga parameter to true.

The compensation steps can be defined by specifying the CompensateWith parameter.

{
  "Id": "Saga-Sample",
  "Version": 1,
  "DataType": "MyApp.MyDataClass, MyApp",
  "Steps": [
    {
      "Id": "Hello",
      "StepType": "MyApp.HelloWorld, MyApp",
      "NextStepId": "MySaga"
    },    
    {
      "Id": "MySaga",
      "StepType": "WorkflowCore.Primitives.Sequence, WorkflowCore",
      "NextStepId": "Bye",
      "Saga": true,
      "Do": [
        [
          {
            "Id": "do1",
            "StepType": "MyApp.Task1, MyApp",
            "NextStepId": "do2",
            "CompensateWith": [
              {
                "Id": "undo1",
                "StepType": "MyApp.UndoTask1, MyApp"
              }
            ]
          },
          {
            "Id": "do2",
            "StepType": "MyApp.Task2, MyApp",
            "CompensateWith": [
              {
                "Id": "undo2-1",
                "NextStepId": "undo2-2",
                "StepType": "MyApp.UndoTask2, MyApp"
              },
              {
                "Id": "undo2-2",
                "StepType": "MyApp.DoSomethingElse, MyApp"
              }
            ]
          }
        ]
      ]
    },    
    {
      "Id": "Bye",
      "StepType": "MyApp.GoodbyeWorld, MyApp"
    }
  ]
}

Id: Saga-Sample
Version: 1
DataType: MyApp.MyDataClass, MyApp
Steps:
- Id: Hello
  StepType: MyApp.HelloWorld, MyApp
  NextStepId: MySaga
- Id: MySaga
  StepType: WorkflowCore.Primitives.Sequence, WorkflowCore
  NextStepId: Bye
  Saga: true
  Do:
  - - Id: do1
      StepType: MyApp.Task1, MyApp
      NextStepId: do2
      CompensateWith:
      - Id: undo1
        StepType: MyApp.UndoTask1, MyApp
    - Id: do2
      StepType: MyApp.Task2, MyApp
      CompensateWith:
      - Id: undo2-1
        NextStepId: undo2-2
        StepType: MyApp.UndoTask2, MyApp
      - Id: undo2-2
        StepType: MyApp.DoSomethingElse, MyApp
- Id: Bye
  StepType: MyApp.GoodbyeWorld, MyApp