Slides from my talk at ISTA 2016 - https://www.istacon.org/Sessions/Sessions?year=2016

2. 15 – 16 November, SofiaISTACon.org
Event Sourcing
By Vladik Khononov
A New Dimension in Software Design

3. 15 – 16 November, SofiaISTACon.org

4. 15 – 16 November, SofiaISTACon.org

5. 15 – 16 November, SofiaISTACon.org

6. 15 – 16 November, SofiaISTACon.org
Agenda
• How it happened
• Why it happened
• How event sourcing solves the problem
• Why event sourcing benefits the company

7. 15 – 16 November, SofiaISTACon.org
Call Center Management

8. 15 – 16 November, SofiaISTACon.org
LEAD
• Id
• Name
• Email
• Phone
• Status (Available / Follow-up / Closed / Converted)

9. 15 – 16 November, SofiaISTACon.org
Name Email Phone Status
Stefan Ivanov stefan@ivanov.com 03-27243457 Available
Viktor Kovachev viktor@kovachev.com 08-8332491 Available
Martin Mateev martin@mateev.com 04-8537112 Available
Lilyana Yankov lilyana@yankov.com 04-6092212 Available

10. 15 – 16 November, SofiaISTACon.org
Name Email Phone Status
Stefan Ivanov stefan@ivanov.com 03-27243457 Available
Viktor Kovachev viktor@kovachev.com 08-8332491 Available
Martin Mateev martin@mateev.com 04-8537112 Available
Lilyana Yankov lilyana@yankov.com 04-6092212 Available

11. 15 – 16 November, SofiaISTACon.org

12. 15 – 16 November, SofiaISTACon.org
public class Lead {
public long Id { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public LeadStatus Status { get; set; }
public DateTime? FollowupOn { get; set; }
}

13. 15 – 16 November, SofiaISTACon.org

14. 15 – 16 November, SofiaISTACon.org
SELECT * FROM leads
WHERE [name] LIKE ‘%name%’ OR
[phone] LIKE ‘%phone%’ OR
[email] LIKE ‘%email%’;

15. WTF???
ISTACon.org

16. 15 – 16 November, SofiaISTACon.org
Lead #1410
Name Viktor Radkov
Email viktor@radkov.com
Phone 09-9801298
Status Available

17. 15 – 16 November, SofiaISTACon.org

18. 15 – 16 November, SofiaISTACon.org
PM

19. 15 – 16 November, SofiaISTACon.org
…1 month later

20. 15 – 16 November, SofiaISTACon.org

21. 15 – 16 November, SofiaISTACon.org
PM

22. 15 – 16 November, SofiaISTACon.org
…2 months later

23. 15 – 16 November, SofiaISTACon.org

24. 15 – 16 November, SofiaISTACon.org
PM

25. 15 – 16 November, SofiaISTACon.org
Search on stale data
Status change dates
Audit log for BI

26. 15 – 16 November, SofiaISTACon.org
PM

27. 15 – 16 November, SofiaISTACon.org
PM

28. 15 – 16 November, SofiaISTACon.org
public class Lead {
public long Id { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public LeadStatus Status { get; set; }
public DateTime? FollowupOn { get; set; }
}

29. 15 – 16 November, SofiaISTACon.org
Name Email Phone Status Follow-up
Stefan Ivanov stefan@ivanov.com 03-27243457 Available

30. 15 – 16 November, SofiaISTACon.org
Name Email Phone Status Follow-up Date
Stefan Ivanov stefan@ivanov.com 050-8139904 Follow-up 23/11/2016

31. 15 – 16 November, SofiaISTACon.org
Name Email Phone Status Follow-up Date
Stefan Ivanov stefan@ivanov.com 050-8139904 Converted

32. 15 – 16 November, SofiaISTACon.org
Name Email Phone Status Follow-up Date
Stefan Ivanov stefan@ivanov.com 050-8139904 Converted

33. 15 – 16 November, SofiaISTACon.org

34. 15 – 16 November, SofiaISTACon.org
Event Sourcing

35. 15 – 16 November, SofiaISTACon.org
Changes
=
First class citizens
=
Events

36. 15 – 16 November, SofiaISTACon.org
Lead Events
• Lead Was Initialized (Id)
• Status Changed (NewStatus)
• Name Changed (NewName)
• Contact Information Changed (NewEmail, NewPhone)
• Followup Set (Date)

37. 15 – 16 November, SofiaISTACon.org
Lead: Stefan Ivanov
• Lead Was Initialized (1410)
• Status Changed (Available)
• Contact Information Changed (stefan@ivanov.com, 03-27243457)
• Status Changed (Followup)
• Followup Set (23/11/2016)
• Contact Information Changed (stefan@ivanov.com, 050-8139904)
• Status Changed (Converted)

38. 15 – 16 November, SofiaISTACon.org
public class Lead {
public long Id { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public LeadStatus Status { get; set; }
public DateTime? FollowupOn { get; set; }
public void Apply(LeadWasInitialized event) {…}
public void Apply(StatusChanged event) {…}
public void Apply(NameChanged event) {…}
public void Apply(ContactInfoChanged event) {…}
public void Apply(FollowupSet event) {…}
}

39. 15 – 16 November, SofiaISTACon.org
public class Lead {
public long Id { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public LeadStatus Status { get; set; }
public DateTime? FollowupOn { get; set; }
public void Apply(LeadWasInitialized event) {…}
public void Apply(StatusChanged event) {…}
public void Apply(NameChanged event) {…}
public void Apply(ContactInfoChanged event) {…}
public void Apply(FollowupSet event) {…}
}
Apply(StatusChanged event) {
this.Status = event.NewStatus;
}

40. 15 – 16 November, SofiaISTACon.org
public class Lead {
public long Id { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public LeadStatus Status { get; set; }
public DateTime? FollowupOn { get; set; }
public void Apply(LeadWasInitialized event) {…}
public void Apply(StatusChanged event) {…}
public void Apply(NameChanged event) {…}
public void Apply(ContactInfoChanged event) {…}
public void Apply(FollowupSet event) {…}
}
Apply(NameChanged event) {
this.Name = event.NewName;
}

41. 15 – 16 November, SofiaISTACon.org
public class Lead {
public long Id { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public LeadStatus Status { get; set; }
public DateTime? FollowupOn { get; set; }
public void Apply(LeadWasInitialized event) {…}
public void Apply(StatusChanged event) {…}
public void Apply(NameChanged event) {…}
public void Apply(ContactInfoChanged event) {…}
public void Apply(FollowupSet event) {…}
}
Apply(ContactInfoChanged event) {
this.Phone = event.NewPhone;
this.Email = event.NewEmail;
}

42. 15 – 16 November, SofiaISTACon.org
public class Lead {
public long Id { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public LeadStatus Status { get; set; }
public DateTime? FollowupOn { get; set; }
public void Apply(LeadWasInitialized event) {…}
public void Apply(StatusChanged event) {…}
public void Apply(NameChanged event) {…}
public void Apply(ContactInfoChanged event) {…}
public void Apply(FollowupSet event) {…}
}
Apply(FollowupSet event) {
this.FollowUpOn = event.Date;
}

43. 15 – 16 November, SofiaISTACon.org
Lead: Stefan Ivanov
Lead Was Initialized (1410)
Status Changed (Available)
Contact Information Changed (stefan@ivanov.com,03-27243457)
Status Changed (Converted)
Status Changed (Followup)
Followup Set (23/11/2016)
Contact Information Changed (stefan@ivanov.com, 050-8139904)

44. 15 – 16 November, SofiaISTACon.org
Name Email Phone Status Follow-up Date
Stefan Ivanov stefan@ivanov.com 050-8139904 Converted

45. 15 – 16 November, SofiaISTACon.org
Lead: Stefan Ivanov
Lead Was Initialized (1410)
Status Changed (Available)
Contact Information Changed (stefan@ivanov.com,03-27243457)
Status Changed (Converted)
Status Changed (Followup)
Followup Set (23/11/2016)
Contact Information Changed (stefan@ivanov.com, 050-8139904)

46. 15 – 16 November, SofiaISTACon.org
Lead: Stefan Ivanov
Lead Was Initialized (1410)
Status Changed (Available)
Contact Information Changed (stefan@ivanov.com,03-27243457)

47. 15 – 16 November, SofiaISTACon.org
Lead: Stefan Ivanov
Lead Was Initialized (1410)
Status Changed (Available)
Contact Information Changed (stefan@ivanov.com,03-27243457)
Status Changed (Followup)
Followup Set (23/11/2016)
Contact Information Changed (stefan@ivanov.com, 050-8139904)

48. 15 – 16 November, SofiaISTACon.org
Lead: Stefan Ivanov
Lead Was Initialized (1410)
Status Changed (Available)
Contact Information Changed (stefan@ivanov.com,03-27243457)
Status Changed (Converted)
Status Changed (Followup)
Followup Set (23/11/2016)
Contact Information Changed (stefan@ivanov.com, 050-8139904)

49. 15 – 16 November, SofiaISTACon.org
public class Lead {
public long Id { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public LeadStatus Status { get; set; }
public DateTime? FollowupOn { get; set; }
}

50. 15 – 16 November, SofiaISTACon.org
Lead: Stefan Ivanov
Lead Was Initialized (1410)
Status Changed (Available)
Contact Information Changed (stefan@ivanov.com,03-27243457)
Status Changed (Converted)
Status Changed (Followup)
Followup Set (23/11/2016)
Contact Information Changed (stefan@ivanov.com, 050-8139904)

51. 15 – 16 November, SofiaISTACon.org
public class LeadSearch {
public long Id { get; private set; }
…
public List<string> Emails;
public List<string> Phones;
…
public void Apply(ContactInfoChanged event) {…}
…
}
Apply(ContactInfoChanged event) {
this.Phones.Append(event.NewPhone);
this.Emails.Append(event.NewEmail);
}

52. 15 – 16 November, SofiaISTACon.org
public class LeadStatusChangesModel {
public long Id { get; set; }
public List<StatusLog> StatusChangesLog;
…
public void Apply(StatusChanged event) {…}
…
}
Apply(StatusChanged event) {
this.StatusChangesLog.Append(
new StatusLog(event.NewStatus,
DateTime.Now);
);

53. 15 – 16 November, SofiaISTACon.org
public class LeadStatusChangesModel {
public long Id { get; set; }
public List<StatusLog> StatusChangesLog;
…
}
public class Lead {
public long Id { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public LeadStatus Status { get; set; }
public DateTime? FollowupOn { get; set; }
…
}
public class LeadSearch {
public long Id { get; private set; }
public List<string> Emails;
public List<string> Phones;
…
}

54. 15 – 16 November, SofiaISTACon.org
Lead: Stefan Ivanov
Lead Was Initialized (1410)
Status Changed (Available)
Contact Information Changed (stefan@ivanov.com,03-27243457)
Status Changed (Converted)
Status Changed (Followup)
Followup Set (23/11/2016)
Contact Information Changed (stefan@ivanov.com, 050-8139904)

55. 15 – 16 November, SofiaISTACon.org
Events = Source of Truth
Event Sourcing

56. 15 – 16 November, SofiaISTACon.org

57. 15 – 16 November, SofiaISTACon.org

58. 15 – 16 November, SofiaISTACon.org

59. 15 – 16 November, SofiaISTACon.org
Storage: Event Store

60. 15 – 16 November, SofiaISTACon.org
Event Store API: The Good News
Append(Entity Id + New events)
GetEvents(Entity Id)Event1,
Event2,
Event3,
….

61. 15 – 16 November, SofiaISTACon.org
Key (Entity Id) Value (Events list)
Lead #1410 1. LeadWasInitialized(1410)
2. StatusChanged(Available)
3. NameChanged(“Martin Mateev”)
4. StatusChanged(Converted)
Lead #1406 1. LeadWasInitialized(1406)
2. StatusChanged(Available’’’)
3. NameChanged(“Lilyana Yankov”)

62. 15 – 16 November, SofiaISTACon.org
Event Store API: The Good News
Append(Entity Id + New events)
GetEvents(Entity Id)Event1,
Event2,
Event3,
….

63. 15 – 16 November, SofiaISTACon.org
Event Store API: The Bad News
Append(Entity Id + New events)
GetEvents(Entity Id)Event1,
Event2,
Event3,
….

64. 15 – 16 November, SofiaISTACon.org
CQRS
Command Query Responsibility Segregation

65. 15 – 16 November, SofiaISTACon.org
CQRS
• Command - write data
• Query - read data
• A use case can be either Command or Query. Never both

66. 15 – 16 November, SofiaISTACon.org
Queries
Read Model
Read DB
Commands
Write Model
Writes DB
Projection engine

67. 15 – 16 November, SofiaISTACon.org
Event Sourced Model (Write)
Lead #1410 1. LeadWasInitialized(1410)
2. StatusChanged(Available)
3. NameChanged(“Martin Mateev”)
4. StatusChanged(Closed)
…
1000. StatusChanged(FollowUp)
1001. FollowupSet(16/11/2017)
Read Model
Id 1410
Name Martin Mateev
Status Followup
FollowupOn (Empty)
Email …
Phone …

68. 15 – 16 November, SofiaISTACon.org
Queries
Read Model
Read DB
Commands
Write Model
Writes DB
Projection engine

69. 15 – 16 November, SofiaISTACon.org
Event Sourced Model (Write)
Lead #1410 1. LeadWasInitialized(1410)
2. StatusChanged(Available)
3. NameChanged(“Martin Mateev”)
4. StatusChanged(Closed)
5. StatusChanged(Available)
6. NameChanged(“Viktor Rumenov”)
Read Model
Id 1410
Phone …
Status Available
FollowupOn (Empty)
Email …
Name Martin Mateev

70. 15 – 16 November, SofiaISTACon.org
public class Lead {
public long Id { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public LeadStatus Status { get; set; }
public DateTime? FollowupOn { get; set; }
public void Apply(LeadWasInitialized event) {…}
public void Apply(StatusChanged event) {…}
public void Apply(NameChanged event) {…}
public void Apply(ContactInfoChanged event) {…}
public void Apply(FollowupSet event) {…}
}
Apply(NameChanged event) {
this.Name = event.NewName;
}

71. 15 – 16 November, SofiaISTACon.org
Queries
Read Model
Read DB
Commands
Event Sourcing
Event Store
Projection engine

72. 15 – 16 November, SofiaISTACon.org
Queries
Read Model
Read DB
Commands
Write Model
Writes DB
Projection
engine
Projection
• RDBMS
• Documents
• Graphs
• Files

73. 15 – 16 November, SofiaISTACon.org
Queries
Read Model
Commands
Write Model
Writes DB
Projection
engine
Projection
• RDBMS
• Documents
• Graphs
• Files
• Multiple DBs
Read DBs

74. 15 – 16 November, SofiaISTACon.org
Queries
Read Model
Commands
Write Model
Writes DB
Projection
engine
Read DBs
Concurrency
• Pessimistic
• Optimistic
• Optimistic on steroids

75. 15 – 16 November, SofiaISTACon.org
SetFollowupCommand + StatusChangeEvent => Collision
ChangeNameCommand + StatusChangeEvent => OK

76. 15 – 16 November, SofiaISTACon.org
Event Sourcing + CQRS
• Flexible business domain modeling
• Insane scalability and availability
• Rock solid infrastructure
• …look great on your C.V.

77. 15 – 16 November, SofiaISTACon.org

78. 15 – 16 November, SofiaISTACon.org
CQRS: When?
Event Sourcing ➡ CQRS
Non-functional benefits

79. 15 – 16 November, SofiaISTACon.org
Event Sourcing
CQRS

80. 15 – 16 November, SofiaISTACon.org
Event Sourcing: When?
?

81. 15 – 16 November, SofiaISTACon.org
Subdomains
Generic, Supporting, Core

82. 15 – 16 November, SofiaISTACon.org

83. 15 – 16 November, SofiaISTACon.org
Subdomains
Generic, Supporting, Core

84. 15 – 16 November, SofiaISTACon.org
CREATIVE CATALOG
CAMPAIGN PUBLISHING
BILLING USERS MANAGEMENT
LEAD MANAGEMENTCOMMISSIONS CALCULATION
DESK MANAGEMENTVOIP MANAGEMENT
EMAIL CAMPAIGNS

85. 15 – 16 November, SofiaISTACon.org
Generic Subdomains

86. 15 – 16 November, SofiaISTACon.org
CREATIVE CATALOG
CAMPAIGN PUBLISHING
BILLING USERS MANAGEMENT
LEAD MANAGEMENTCOMMISSIONS CALCULATION
DESK MANAGEMENTVOIP MANAGEMENT
EMAIL CAMPAIGN

87. 15 – 16 November, SofiaISTACon.org
CREATIVE CATALOG
CAMPAIGN PUBLISHING
BILLING USERS MANAGEMENT
LEAD MANAGEMENTCOMMISSIONS CALCULATION
DESK MANAGEMENTVOIP MANAGEMENT
EMAIL CAMPAIGN

88. 15 – 16 November, SofiaISTACon.org
Supporting Subdomains

89. 15 – 16 November, SofiaISTACon.org
CREATIVE CATALOG
CAMPAIGN PUBLISHING
BILLING USERS MANAGEMENT
LEAD MANAGEMENTCOMMISSIONS CALCULATION
DESK MANAGEMENTVOIP MANAGEMENT
EMAIL CAMPAIGN

90. 15 – 16 November, SofiaISTACon.org
CREATIVE CATALOG
CAMPAIGN PUBLISHING
BILLING USERS MANAGEMENT
LEAD MANAGEMENTCOMMISSIONS CALCULATION
DESK MANAGEMENTVOIP MANAGEMENT
EMAIL CAMPAIGN

91. 15 – 16 November, SofiaISTACon.org
Core Domains

92. 15 – 16 November, SofiaISTACon.org
CREATIVE CATALOG
CAMPAIGN PUBLISHING
BILLING USERS MANAGEMENT
LEAD MANAGEMENTCOMMISSIONS CALCULATION
DESK MANAGEMENTVOIP MANAGEMENT
EMAIL CAMPAIGN

93. 15 – 16 November, SofiaISTACon.org
Event Sourcing: When?
Core business domains

94. 15 – 16 November, SofiaISTACon.org
Before you try this at home

95. 15 – 16 November, SofiaISTACon.org
Available Event Stores
• http://GetEventStore.com
• NEventStore
• Akka Persistence
• Elastic Event Store (Coming soon)

96. 15 – 16 November, SofiaISTACon.org

97. 15 – 16 November, SofiaISTACon.org
€100 Discount for attendees of ISTA 2016
https://ti.to/webengineers/ddd17/discount/istacon2016

98. 15 – 16 November, SofiaISTACon.org
Domain-Driven Design
• How to identify subdomains?
• How to define business entities?
• How do define events?
• How to talk to business experts?

99. 15 – 16 November, SofiaISTACon.org

100. 15 – 16 November, SofiaISTACon.org
Thank you!
@vladikk
vladikk.com
vladikkhononov
vladik@khononov.com