WorkflowCore.Sample17

Saga transaction with compensation sample

Illustrates how 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>()
	)
	.OnError(Models.WorkflowErrorHandling.Retry, TimeSpan.FromSeconds(5))
	.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>()
	)
	.CompensateWith<CleanUp>()
	.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

A saga transaction can be expressed in JSON, 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"
    }
  ]
}