public void MoveForward()
{
Direction = SagaDirection.Forward;
}
public void MoveBackward()
{
Direction = SagaDirection.Backward;
}
public SagaStateProxy Process(T sagaState, SagaStateProxy sagaStateProxy)
{
SagaStateProxy result;
var types = Assembly.GetCallingAssembly().GetTypes()
.FirstOrDefault(x => x.BaseType == typeof(SagaDefinition <>).MakeGenericType(sagaState.GetType()));
var sagaDefinition = (SagaDefinition <T>)Activator.CreateInstance(types, new object[] { (T)sagaState });
if (sagaStateProxy.IsCompleted)
{
throw new SagaException(sagaState.SagaId, "The saga is already completed");
}
// start from beginning
var stepDefinition = sagaDefinition.GetStepWithName(sagaStateProxy.NextState);
// get direction
// forward or backward.
SagaDirection sagaDirection =
sagaStateProxy is EmptySagaState ? SagaDirection.Forward : sagaStateProxy.Direction;
if (!(sagaStateProxy is EmptySagaState))
{
sagaState = (T)sagaStateProxy.SagaState;
}
switch (sagaDirection)
{
case SagaDirection.Forward:
result = ProcessForward();
break;
case SagaDirection.Backward:
result = ProcessBackward();
break;
default:
throw new SagaException(sagaState.SagaId, "Saga direction is not correct");
}
return(result);
SagaStateProxy ProcessBackward()
{
var isCompleted = sagaDefinition.IsCompleted(stepDefinition.Name, SagaDirection.Backward);
// Execute the participant.
var command = stepDefinition.CompensationStage.Invoke();
var definitionCompensationHandler = stepDefinition.CompensationHandler(command, sagaState);
SagaStateProxy newProxy;
if (definitionCompensationHandler is NoReplyCommandEndpoint)
{
// what happen if publish message is failed
var version = sagaStateProxy.Version + 1;
newProxy = new SagaStateProxy(sagaState, (bool)isCompleted, DateTime.Now,
version, stepDefinition.Name,
stepDefinition.PreviousStep == null ? stepDefinition.Name : stepDefinition.PreviousStep.Name,
sagaDefinition.GetType());
newProxy.MoveBackward();
}
else
{
var version = sagaStateProxy.Version + 1;
newProxy = new SagaStateProxy(sagaState, false, DateTime.Now, version,
stepDefinition.Name,
$"WaitingFor_{stepDefinition.Name}",
sagaDefinition.GetType());
newProxy.MoveBackward();
}
return(newProxy);
}
// Handler must be handle all cases from retries or throw an exception. The engine only produce sagaProxy
SagaStateProxy ProcessForward()
{
var isCompleted = sagaDefinition.IsCompleted(stepDefinition.Name, SagaDirection.Forward);
SagaStateProxy newProxy;
// Execute the participant.
try
{
var command = stepDefinition.ParticipantStage.Invoke();
var definitionParticipantHandler = stepDefinition.ParticipantHandler(command, sagaState);
if (definitionParticipantHandler is NoReplyCommandEndpoint)
{
// what happen if publish message is failed
var version = sagaStateProxy.Version + 1;
newProxy = new SagaStateProxy(sagaState, (bool)isCompleted, DateTime.Now,
version, stepDefinition.Name,
stepDefinition.NextStep == null ? stepDefinition.Name : stepDefinition.NextStep.Name,
sagaDefinition.GetType());
newProxy.MoveForward();
}
else
{
// send the message, getting confirmation from message broker and then saving to the database.
_sagaPublisher.Publish(definitionParticipantHandler.SagaCommandContext, definitionParticipantHandler.Data);
var version = sagaStateProxy.Version + 1;
newProxy = new SagaStateProxy(sagaState, isCompleted, DateTime.Now, version,
stepDefinition.Name,
$"WaitingFor_{stepDefinition.Name}",
sagaDefinition.GetType());
newProxy.MoveForward();
}
}
catch (Exception e)
{
var version = sagaStateProxy.Version + 1;
newProxy = new SagaStateProxy(sagaState, false, DateTime.Now,
version, stepDefinition.Name,
stepDefinition.PreviousStep == null ? stepDefinition.Name : stepDefinition.PreviousStep.Name,
sagaDefinition.GetType());
newProxy.Error = new SagaException(newProxy.SagaId, e.Message);
newProxy.MoveBackward();
}
return(newProxy);
}
}