Będę mówił o tym jak radzić sobie z zastanym stanem świata. Dlaczego z zastanym? Bo skoro już reagujemy na zdarzenie, to coś się stało i się nie odstanie. Koniec kropka. W trakcie wykładu postaram się wprowadzić koncepcję zdarzeń domenowych, opowiedzieć gdzie plasują się one na płaszczyźnie szeroko pojętego i przeładowanego w IT słowa event. Opowiem jak implementować zdarzenia, co jest zdarzeniem, a co nie jest oraz jakie benefity i koszty wnoszą do naszego kodu. Pokażę także, jak zdarzenia wykorzystać żeby ułatwić sobie pracę oraz podzielę się ze słuchaczami kilkoma regułami kciuka, które stosuję w trakcie pracy ze zdarzeniami.

1. Domain Events
Czyli jak radzić sobie z rzeczywistością!
Mateusz Stasch | 2016.04.11

2. Mateusz Stasch
@mattstasch
http://mattstasch.net

3. ?

5. Domain Events

6. Domain Events

7. UI
Events
Event Loop
…
Application
Events
EDA
…
…
Domain
Events

8. UI
Events
Event Loop
…
Application
Events
EDA
…
…
Domain
Events

9. Domain event is something that happened
that domain experts care about.
Anonymous

10. Domain(T0) Domain(T1)
Operation
E

11. NOW

12. C D E
H

13. C D E
H1 H2

14. C D E
H1 H2
Ext. System

15. C D E
H1 H2
Ext. System
Sync
Async

17. public void RegisterCardPayment(EntityId id, CardPayment paymentDetails)
{
// Validation...
var caseToBePaid = _caseDao.GetById(id);
// It was not so simple... ;)
caseToBePaid.Payments.Add(paymentDetails);
caseToBePaid.RefreshOutstandingBalance();
_mmeGateway.RegisterPayment(/*...*/);
if (paymentDetails.CardType == CardType.Credit)
{
// Message generation...
_mailGateway.Send(/*...*/);
}
/* Send to PDA... */
}

18. Business Logic PDA MME Mail

19. Business Logic PDA MME Mail
Test Scope

20. Business Logic PDA MME Mail
CBL * CPDA
CMME CMail* *
Test Scope

21. public void RegisterCardPayment(EntityId id, CardPayment paymentDetails)
{
// Validation...
var caseToBePaid = _caseDao.GetById(id);
// It was not so simple... ;)
caseToBePaid.Payments.Add(paymentDetails);
caseToBePaid.RefreshOutstandingBalance();
_mmeGateway.RegisterPayment(/*...*/);
if (paymentDetails.CardType == CardType.Credit)
{
// Message generation...
_mailGateway.Send(/*...*/);
}
/* Send to PDA... */
}

22. public void RegisterCardPayment(EntityId id,
CardPayment paymentDetails)
{
// Validation...
var caseToBePaid = _caseDao.GetById(id);
// It was not so simple... ;)
caseToBePaid.Payments.Add(paymentDetails);
caseToBePaid.RefreshOutstandingBalance();
_eventBus.Raise(new CardPaymentRegisteredEvent
{
Id = id,
Details = paymentDetails
});
}

23. public class CardPaymentRegisteredEvent : Event
{
public CardPayment Details { get; set; }
}

24. Business Logic PDA MME Mail

25. public class MmePaymentsHandler
: IEventHandler<CardPaymentRegisteredEvent>
{
private MMEGateway _mmeGateway;
/* ctor(MMEGateway Gateway)... */
public void Handle(CardPaymentRegisteredEvent @event)
{
if (@event.Details.CardType == CardType.Credit)
{
_mmeGateway.Send(/*...*/);
}
}
}

26. public class MmePaymentsHandler
: IEventHandler<CardPaymentRegisteredEvent>
{
private MMEGateway _mmeGateway;
/* ctor(MMEGateway Gateway)... */
public void Handle(CardPaymentRegisteredEvent @event)
{
if (@event.Details.CardType == CardType.Credit)
{
_mmeGateway.Send(/*...*/);
}
}
}

27. Event Bus
Listen
Business Logic
Publish
Listen
PDA
MME
Listen
Mail

28. Event Bus
Listen
Business Logic
Publish
Listen
PDA
MME
Listen
Mail

29. Event Bus
Listen
Business Logic
Publish
Listen
PDA
MME
Listen
Mail
CBL + CPDA + CMME + CMail

30. public class MmePaymentsHandler
: IEventHandler<CardPaymentRegisteredEvent>
{
private MMEGateway _mmeGateway;
/* ctor(MMEGateway Gateway)... */
public void Handle(CardPaymentRegisteredEvent @event)
{
if (@event.Details.CardType == CardType.Credit)
{
_mmeGateway.Send(/*...*/);
}
}
}

31. Event Bus
Listen
Business Logic
Publish
Listen
PDA
MME
Listen
Mail
Listen
…
Listen
…

32. Nie wiem ilu Was jest, kiedy i w
jakiej kolejności wykonacie
pracę oraz jaki będzie jej wynik

33. SendEmailEvent
#1

34. SendEmailEvent
Życzenie, nie fakt!
#1

35. NOW
#1

36. PaymentRejectedEvent
Zrób coś, bo Payment został odrzucony!
#1

37. Czas przeszły,
tryb dokonany!
#1

38. Fakt, a nie życzenie!
#1

39. _eventBus.Raise(new CardPaymentRegisteredEvent
{
Id = id,
Details = paymentDetails,
Case = caseToBePaid
});
#2

40. _eventBus.Raise(new CardPaymentRegisteredEvent
{
Id = id,
Details = paymentDetails,
Case = caseToBePaid
});
#2

41. Zdarzenie powinno
być małe* i serializowalne
#2

42. 2
1
#3

43. public void RegisterCardPayment(EntityId id,
CardPayment paymentDetails)
{
var caseToBePaid = _caseDao.GetById(id);
caseToBePaid.Payments.Add(paymentDetails);
caseToBePaid.RefreshOutstandingBalance();
if (caseToBePaid.OutstandingBalance.IsZero)
{
caseToBePaid.MarkAsPaid();
}
/* MME */
/* Mail */
/* Send to PDA... */
}

44. public void RegisterCardPayment(EntityId id,
CardPayment paymentDetails)
{
var caseToBePaid = _caseDao.GetById(id);
caseToBePaid.Payments.Add(paymentDetails);
caseToBePaid.RefreshOutstandingBalance();
if (caseToBePaid.OutstandingBalance.IsZero)
{
caseToBePaid.MarkAsPaid();
}
/* MME */
/* Mail */
/* Send to PDA... */
}

45. Nie wiem ilu Was jest, kiedy i w
jakiej kolejności wykonacie
pracę oraz jaki będzie jej wynik
#3

46. Nie polegaj na
konkretnej
implementacji!
Infrastruktury zdarzeń.
#3

47. public void RegisterCardPayment(EntityId id,
CardPayment paymentDetails)
{
var caseToBePaid = _caseDao.GetById(id);
// It was not so simple... ;)
caseToBePaid.Payments.Add(paymentDetails);
caseToBePaid.RefreshOutstandingBalance();
if (caseToBePaid.OutstandingBalance.IsZero)
{
_eventBus.Raise(new CasePaidEvent { Id = id });
}
_eventBus.Raise(new CardPaymentRegisteredEvent
{
Id = id,
Details = paymentDetails
});
}
public void RegisterCashPayment(EntityId id /*...*/)

48. public void RegisterCardPayment(EntityId id,
CardPayment paymentDetails)
{
var caseToBePaid = _caseDao.GetById(id);
// It was not so simple... ;)
caseToBePaid.Payments.Add(paymentDetails);
caseToBePaid.RefreshOutstandingBalance();
if (caseToBePaid.OutstandingBalance.IsZero)
{
_eventBus.Raise(new CasePaidEvent { Id = id });
}
_eventBus.Raise(new CardPaymentRegisteredEvent
{
Id = id,
Details = paymentDetails
});
}
public void RegisterCashPayment(EntityId id /*...*/)

49. public void RegisterCardPayment(EntityId id,
CardPayment paymentDetails)
{
var caseToBePaid = _caseDao.GetById(id);
// It was not so simple... ;)
caseToBePaid.Payments.Add(paymentDetails);
caseToBePaid.RefreshOutstandingBalance();
if (caseToBePaid.OutstandingBalance.IsZero)
{
_eventBus.Raise(new CasePaidEvent { Id = id });
}
_eventBus.Raise(new CardPaymentRegisteredEvent
{
Id = id,
Details = paymentDetails
});
}
public void RegisterCashPayment(EntityId id /*...*/)

50. public void RegisterCardPayment(EntityId id,
CardPayment paymentDetails)
{
var caseToBePaid = _caseDao.GetById(id);
// It was not so simple... ;)
caseToBePaid.Payments.Add(paymentDetails);
caseToBePaid.RefreshOutstandingBalance();
if (caseToBePaid.OutstandingBalance.IsZero)
{
_eventBus.Raise(new CasePaidEvent { Id = id });
}
_eventBus.Raise(new CardPaymentRegisteredEvent
{
Id = id,
Details = paymentDetails
});
}
public void RegisterCashPayment(EntityId id /*...*/)
Utrata kontroli

52. public void RegisterCardPayment(EntityId id,
CardPayment paymentDetails)
{
var caseToBePaid = _caseDao.GetById(id);
// It was not so simple... ;)
caseToBePaid.Payments.Add(paymentDetails);
caseToBePaid.RefreshOutstandingBalance();
_eventBus.Raise(new CardPaymentRegisteredEvent
{
Id = id,
Details = paymentDetails
});
}
public void RegisterCashPayment(EntityId id /*...*/)

53. Jedno zdarzenie ma
jedno źródło!
#4

54. public void AddGood(EntityId id, Good good)
{
var @case = _caseDao.GetById(id);
@case.AddGood(good);
_mmeGateway.Send(/*...*/ @case.Balance);
/* Other stuff */
}
#5

55. public void AddGood(EntityId id, Good good)
{
var @case = _caseDao.GetById(id);
@case.AddGood(good);
_mmeGateway.Send(/*...*/ @case.Balance);
/* Other stuff */
}
#5

56. #5public class GoodAddedEvent : IEvent
{
public EntityId Id { get; set; }
public DateTimeOffset RaisedAt { get; set; }
public Good Good { get; set; }
public Money Balance { get; set; }
}

57. #5public class GoodAddedEvent : IEvent
{
public EntityId Id { get; set; }
public DateTimeOffset RaisedAt { get; set; }
public Good Good { get; set; }
public Money Balance { get; set; }
}

58. public void AddGood(EntityId id, Good good)
{
var @case = _caseDao.GetById(id);
@case.AddGood(good);
/* Raise Event */
_mailGateway.Send(/*...*/ @case.OutstandingBalance);
/* Other stuff */
}
#5

59. #5
Nie modeluj zdarzenia dla
konkretnego handlera

60. ReCap
• Fakt, a nie życzenie!
• Obiekt zdarzenia powinien być mały
• Nie polegaj na skutkach ubocznych swojej
implementacji
• Jedno zdarzenie ma jedno źródło
• Nie modeluj zdarzenia dla jednego handlera
• Nie używajcie EF-a.

61. Jaką logikę, przerzucić
do handlera?

63. Refactoring
 Powiadomienia(Maile, SMSy)
 Integracje z zew. systemami
o ile nie są krytyczne*
 Eager Data Derivation
 Generowanie dokumentów/raportów
 Unieważnianie :D Cache

64. MVP
Niestety na przykładzie EF-a

65. public interface IEvent
{
int Id { get; set; }
Type EntityType { get; set; }
}
public interface IEventHandler<TEvent>
where TEvent : IEvent
{
void Handle(TEvent @event);
}

66. public interface IEventSource
{
IList<IEvent> Events { get; }
}

67. this.Raise(new CasePaidEvent() {Id = id});

68. private void ApplyEvents()
{
var processed = new List<IEvent>();
for (;;)
{
var events = ChangeTracker.Entries<IEventSource>()
.SelectMany(x => x.Entity.Events)
.Except(processed)
.ToList();
if (!events.Any()) break;
foreach (var @event in events)
{
_eventDispatcher.Apply(@event);
processed.Add(@event);
}
}
}
public override int SaveChanges() {
ApplyEvents();
base.SaveChanges();
}

69. private void ApplyEvents()
{
var processed = new List<IEvent>();
for (;;)
{
var events = ChangeTracker.Entries<IEventSource>()
.SelectMany(x => x.Entity.Events)
.Except(processed)
.ToList();
if (!events.Any()) break;
foreach (var @event in events)
{
_eventDispatcher.Apply(@event);
processed.Add(@event);
}
}
}
public override int SaveChanges() {
ApplyEvents();
base.SaveChanges();
}

70. private void ApplyEvents()
{
var processed = new List<IEvent>();
for (;;)
{
var events = ChangeTracker.Entries<IEventSource>()
.SelectMany(x => x.Entity.Events)
.Except(processed)
.ToList();
if (!events.Any()) break;
foreach (var @event in events)
{
_eventDispatcher.Apply(@event);
processed.Add(@event);
}
}
}
public override int SaveChanges() {
ApplyEvents();
base.SaveChanges();
}

71. private void ApplyEvents()
{
var processed = new List<IEvent>();
for (;;)
{
var events = ChangeTracker.Entries<IEventSource>()
.SelectMany(x => x.Entity.Events)
.Except(processed)
.ToList();
if (!events.Any()) break;
foreach (var @event in events)
{
_eventDispatcher.Apply(@event);
processed.Add(@event);
}
}
}
public override int SaveChanges() {
ApplyEvents();
base.SaveChanges();
}

72. private void ApplyEvents()
{
var processed = new List<IEvent>();
for (;;)
{
var events = ChangeTracker.Entries<IEventSource>()
.SelectMany(x => x.Entity.Events)
.Except(processed)
.ToList();
if (!events.Any()) break;
foreach (var @event in events)
{
_eventDispatcher.Apply(@event);
processed.Add(@event);
}
}
}
public override int SaveChanges() {
ApplyEvents();
base.SaveChanges();
}

73. public class EventDispatcher : IEventDispatcher
{
/*...*/
public void Apply(IEvent @event)
{
// ... Call generic ApplyTyped
}
protected void ApplyTyped<TEvent>(TEvent @event)
where TEvent : IEvent
{
var handlers = _scope.Resolve<IEnumerable<IEventHandler<TEvent>>>();
foreach (var eventHandler in handlers)
{
eventHandler.Handle(@event);
}
}
}

74. public class EventDispatcher : IEventDispatcher
{
/*...*/
public void Apply(IEvent @event)
{
// ... Call generic ApplyTyped
}
protected void ApplyTyped<TEvent>(TEvent @event)
where TEvent : IEvent
{
var handlers = _scope.Resolve<IEnumerable<IEventHandler<TEvent>>>();
foreach (var eventHandler in handlers)
{
eventHandler.Handle(@event);
}
}
}

75. public void Apply(IEvent @event)
{
try
{
applyTypedMethod.MakeGenericMethod(@event.GetType())
.Invoke(this, new object[] { @event });
}
catch (TargetInvocationException ex)
{
ex.InnerException.PreserveStackTrace();
throw ex.InnerException;
}
}

76. public class AgreementSubmitted : IEvent
{
public DateTime EffectiveDate { get; set; }
public string Note { get; set; }
public int Id { get; set; }
public Type EntityType { get; set; }
public AgreementSubmitted(int id,
DateTime effectiveDate,
string note)
{
Id = id;
EffectiveDate = effectiveDate;
Note = note;
}
}

77. public void Handle(AgreementSubmitted @event)
{
SendEmail(ApprovalRequestEmailCode,
@event.Id, pa => pa.Administrators);
}

78. Event Log jako Log
Historia pewnego włamania...

79. public class EventPersister<TEvent> : IEventHandler<TEvent>
where TEvent : IEvent
{
private readonly IEventStore _eventStore;
public void Handle(TEvent @event)
{
_eventStore.Save(new EventEnvelope<TEvent>(@event));
}
}

80. SELECT * FROM EventLog
WHERE
EntityType = 'NS.Case'
AND Id = 302049
ORDER BY RaisedAt
Id EntityType RaisedAt RaisedBy EventType Content
302049 Domain.Case 2016-01-01 20:54:43.104 56 Events.Case.Created {…}
302049 Domain.Case 2016-01-01 20:55:43.105 56 Events.Case.CardPaymentRegistered {…}
302049 Domain.Case 2016-03-01 15:01:13.554 76 Events.Case.GoodsCollected {…}
302049 Domain.Case 2016-03-01 15:01:13.555 1 Events.Case.Paid {}
302050 Domain.Case 2016-03-01 15:01:13.556 1 Events.Case.Closed {}

81. SELECT * FROM EventLog
WHERE
EntityType = 'NS.Case'
AND Id = 302049
ORDER BY RaisedAt
Id EntityType RaisedAt RaisedBy EventType Content
302049 Domain.Case 2016-01-01 20:54:43.104 56 Events.Case.Created {…}
302049 Domain.Case 2016-01-01 20:55:43.105 56 Events.Case.CardPaymentRegistered {…}
302049 Domain.Case 2016-03-01 15:01:13.554 76 Events.Case.GoodsCollected {…}
302049 Domain.Case 2016-03-01 15:01:13.555 1 Events.Case.Paid {}
302050 Domain.Case 2016-03-01 15:01:13.556 1 Events.Case.Closed {}

82. Event Sourcing
Replay
Entity(TN)

83. Event Storming

84. Pytania?

85. Dzięki!
Domain Events
Czyli jak radzić sobie z rzeczywistością!
Mateusz Stasch | 2016.04.11