The aggregate is dead! Long live the aggregate! - SpringIO.pdf

1. The aggregate is dead! Long live the aggregate!

3. @_sara_p_ Sara Pellegrini @MilanSavic14 Milan Savic

5. The aggregate

6. The aggregate

7. The aggregate An aggregate is a cluster of associated objects that we treat as a unit for the purpose of data changes. From blue book - Domain-Driven Design: Tackling Complexity in the Heart of Software - Eric Evans

8. The aggregate is ... confusing

9. From theory to practice

10. From theory to practice Cluster the ENTITIES and VALUE OBJECTS into AGGREGATES and deﬁne boundaries around each. From blue book - Domain-Driven Design: Tackling Complexity in the Heart of Software - Eric Evans

11. From theory to practice Cluster the ENTITIES and VALUE OBJECTS into AGGREGATES and deﬁne boundaries around each. Choose one ENTITY to be the root of each AGGREGATE, and control all access to the objects inside the boundary through the root. From blue book - Domain-Driven Design: Tackling Complexity in the Heart of Software - Eric Evans

12. From theory to practice Cluster the ENTITIES and VALUE OBJECTS into AGGREGATES and deﬁne boundaries around each. Choose one ENTITY to be the root of each AGGREGATE, and control all access to the objects inside the boundary through the root. Allow external objects to hold reference to the root only. From blue book - Domain-Driven Design: Tackling Complexity in the Heart of Software - Eric Evans

14. Event Storming Education domain

15. Event Storming Education domain 1) A course cannot accept more than N students

16. Event Storming Education domain 1) A course cannot accept more than N students 2) N, the Course Capacity, can change any time to any positive integer different from the current one

17. Event Storming Education domain 1) A course cannot accept more than N students 2) N, the Course Capacity, can change any time to any positive integer different from the current one (even if the number of currently subscribed students is larger than the new value)

18. time

19. Course Created Event time

20. Course Created Event Student Subscribed to Course Event time

21. Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event time

22. Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event Course Capacity Changed Event time

23. Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event Course Capacity Changed Event Create Course Command Subscribe Student to Course Command Unsubscribe Student to Course Command Update Course Capacity Command time

24. Story Telling

25. Story Telling Storytelling is at the heart of human communication.

26. Story Telling Storytelling is at the heart of human communication. Storytelling does not require any special competence/skill.

27. Story Telling Storytelling is at the heart of human communication. Storytelling does not require any special competence/skill. It helps break down the barriers between technicians and business experts.

28. The aggregate is the boundary of consistency

29. The aggregate is the boundary of consistency When a change to any object with the aggregate boundary is committed, all invariants of the whole aggregate must be satisﬁed. From blue book - Domain-Driven Design: Tackling Complexity in the Heart of Software - Eric Evans

30. Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event Course Capacity Changed Event Create Course Command Subscribe Student to Course Command Unsubscribe Student to Course Command Update Course Capacity Command

31. Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event Course Capacity Changed Event Create Course Command Subscribe Student to Course Command Unsubscribe Student to Course Command Update Course Capacity Command 1) A course cannot accept more than N students 2) N, the Course Capacity, can change any time to any positive integer different from the current one

32. Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event Course Capacity Changed Event Create Course Command Subscribe Student to Course Command Unsubscribe Student to Course Command Update Course Capacity Command Course Course Course Course 1) A course cannot accept more than N student 2) N, the Course Capacity, can change any time to any positive integer different from the current one

33. Aggregate does not fit Story Telling

34. Aggregate does not ﬁt with Story Telling

35. Aggregate does not ﬁt with Story Telling It is not naturally part of the story: the story teller is forced to add this element

36. Aggregate does not ﬁt with Story Telling It is not naturally part of the story: the story teller is forced to add this element Should business experts understand what a consistency boundary is?

37. Aggregate does not ﬁt with Story Telling It is not naturally part of the story: the story teller is forced to add this element Should business experts understand what a consistency boundary is? Leads back to the old modelling-ﬁrst/data centric approach. Moves the focus from the behavior to the model.

38. Aggregate Mixes technical and business aspects

39. The nouns become our aggregates Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event Course Capacity Changed Event Create Course Command Subscribe Student to Course Command Unsubscribe Student to Course Command Update Course Capacity Command Course Course Course Course

40. The nouns become our aggregates Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event Course Capacity Changed Event Create Course Command Subscribe Student to Course Command Unsubscribe Student to Course Command Update Course Capacity Command Course Course Course Course

41. The course Course Create Course Command Subscribe Student to Course Command Unsubscribe Student to Course Command Update Course Capacity Command Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event Course Capacity Changed Event

42. The COURSE aggregate <<Aggregate Root>> Course Subscription *

43. The COURSE aggregate <<Aggregate Root>> Course Subscription * Subscribe Student to Course Command Unsubscribe Student to Course Command

44. The COURSE aggregate <<Aggregate Root>> Course Subscription * Subscribe Student to Course Command Unsubscribe Student to Course Command

45. The COURSE aggregate <<Aggregate Root>> Course Subscription * Subscribe Student to Course Command Unsubscribe Student to Course Command Update Course Capacity Command

46. The COURSE aggregate <<Aggregate Root>> Course Subscription * Subscribe Student to Course Command Unsubscribe Student to Course Command Update Course Capacity Command

47. Event sourced COURSE aggregate Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event Course Capacity Changed Event

48. Event sourced COURSE aggregate Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event Course Capacity Changed Event Subscribe Student to Course Command Unsubscribe Student to Course Command

49. Event sourced COURSE aggregate Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event Course Capacity Changed Event Subscribe Student to Course Command Unsubscribe Student to Course Command Update Course Capacity Command

50. Event Storming of this problem: Education domain 1) A course cannot accept more than N students 2) N, the Course Capacity, can change any time to any positive integer different from the current one (even if the number of currently subscribed students is larger than the new value) 3) The course title can change any time to any title different from the current one

51. Event Storming of this problem: Education domain 1) A course cannot accept more than N students 2) N, the Course Capacity, can change any time to any positive integer different from the current one (even if the number of currently subscribed students is larger than the new value) 3) The course title can change any time to any title different from the current one

52. Course Renamed Event

53. Course Renamed Event Rename Course Command

54. Course Renamed Event Rename Course Command Course

55. The larger the Aggregate the greater the contention

56. The boundary of consistency is also the boundary of concurrency

57. Concurrent command execution

58. Concurrent command execution Update Course Capacity Command Rename Course Command

59. Concurrent command execution Update Course Capacity Command Rename Course Command <<Aggregate Root>> Course Subscription * <<Aggregate Root>> Course Subscription *

63. Alternative solution

64. Alternative solution <<Aggregate Root>> Course Subscription *

65. <<Aggregate Root>> Course Subscriptions Subscription * Alternative solution: CourseInfo & CourseSubscription <<Aggregate Root>> Course Info

66. Course CourseInfo & CourseSubscriptions

67. Course More contention Simpler CourseInfo & CourseSubscriptions

68. Course More contention Simpler CourseInfo & CourseSubscriptions Less contention

69. Course More contention Simpler CourseInfo & CourseSubscriptions Less contention Additional complexity ➔ Management of multiple aggregates

70. What if model changes…

71. What if model changes… Now what???

72. What if model changes… Now what??? State Persisted Aggregates - Script Event Sourced Aggregates - ???

76. Refactoring with Event Sourcing Course Created …. Course Renamed Course Capacity Changed …. Course Capacity Changed …. ….

77. Refactoring with Event Sourcing Course Created …. Course Renamed Course Capacity Changed …. Course Capacity Changed …. …. ….

78. Refactoring with Event Sourcing Course Created …. Course Renamed Course Capacity Changed …. Course Capacity Changed …. …. Course Subscriptions Created …. Course Info Created

79. Refactoring with Event Sourcing Course Created …. Course Renamed Course Capacity Changed …. Course Capacity Changed …. …. Course Subscriptions Created …. …. …. Course Info Created

80. Refactoring with Event Sourcing Course Created …. Course Renamed Course Capacity Changed …. Course Capacity Changed …. …. Course Subscriptions Created …. Course Renamed …. …. Course Info Created

81. Refactoring with Event Sourcing Course Created …. Course Renamed Course Capacity Changed …. Course Capacity Changed …. …. Course Subscriptions Created …. Course Renamed Course Capacity Changed …. Course Capacity Changed …. …. Course Info Created

82. Refactoring with Event Sourcing Course Created …. Course Renamed Course Capacity Changed …. Course Capacity Changed …. …. Course Subscriptions Created …. Course Renamed Course Capacity Changed …. Course Capacity Changed …. …. Course Info Created

83. Aggregates Are Hard to Refactor

84. Event Storming of this problem: Education domain 1) A course cannot accept more than N students 2) N, the Course Capacity, can change any time to any positive integer different from the current one (even if the number of currently subscribed students is larger than the new value) 3) The course title can change any time to any title different from the current one 4) The student cannot join more than 10 courses

85. Event Storming of this problem: Education domain 1) A course cannot accept more than N students 2) N, the Course Capacity, can change any time to any positive integer different from the current one (even if the number of currently subscribed students is larger than the new value) 3) The course title can change any time to any title different from the current one 4) The student cannot join more than 10 courses

86. Student Created Event time

87. Student Created Event time Create Student Command

88. Student Created Event Student Subscribed to Course Event time Create Student Command

89. Student Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event time Create Student Command

90. Create Student Command Subscribe Student to Course Command Student Created Event Student Subscribed to Course Event Unsubscribe Student from Course Command Student Unsubscribed from Course Event time

92. Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course Event Course Capacity Changed Event Create Course Command Subscribe Student to Course Command Unsubscribe Student to Course Command Update Course Capacity Command Course Course Course Course

93. Create Student Command Subscribe Student to Course Command Student Created Event Student Subscribed to Course Event Unsubscribe Student from Course Command Student Unsubscribed from Course Event 4) The student cannot join more than 10 courses

94. Create Student Command Subscribe Student to Course Command Student Created Event Student Subscribed to Course Event Unsubscribe Student from Course Command Student Unsubscribed from Course Event Student Student Student 4) The student cannot join more than 10 courses

95. Create Student Command Subscribe Student to Course Command Student Created Event Student Subscribed Course Event Student Unsubscribe Student from Course Command Student Unsubscribed from Course Event

96. The STUDENT aggregate <<Aggregate Root>> Student Subscription *

97. We need some form of synchronization...

98. We need some form of synchronization... Subscribe Student to Course Command

99. Saga We need some form of synchronization... Subscribe Student to Course Command

100. Saga We need some form of synchronization... Subscribe Student to Course Command Subscribe Student to Course Command Subscribe Student to Course Command Student Course 1 1

101. Saga We need some form of synchronization... Subscribe Student to Course Command Subscribe Student to Course Command Subscribe Student to Course Command Student Subscribed Course Event Student Subscribed Course Event Student Course 1 1

102. Saga We need some form of synchronization... Subscribe Student to Course Command Subscribe Student to Course Command Subscribe Student to Course Command Student Subscribed Course Event Student Course 1 1

103. Saga We need some form of synchronization... Subscribe Student to Course Command Subscribe Student to Course Command Subscribe Student to Course Command Student Subscribed Course Event Student Course revert 1 1 2

104. Saga We need some form of synchronization... Subscribe Student to Course Command Subscribe Student to Course Command Subscribe Student to Course Command Student Subscribed Course Event Student Course revert Unsubscribe Student to Course Command Student Unsubscribed Course Event Student 1 1 2 3

105. Transactions that span Multiple Aggregates Could Cause Unnecessary Complexity

106. It's just a long transaction...

107. It's just a long transaction... Long transaction are very common when the business rule spans bounded contexts.

108. It's just a long transaction... Long transaction are very common when the business rule spans bounded contexts. But when the rule spans multiple aggregates in the same bounded context?

109. It's just a long transaction... Long transaction are very common when the business rule spans bounded contexts. But when the rule spans multiple aggregates in the same bounded context? Is this a necessary complexity or it can be avoided?

111. ● Does not ﬁt the story telling

112. ● Does not ﬁt the story telling ● Puts focus on model instead of behaviour

113. ● Does not ﬁt the story telling ● Puts focus on model instead of behaviour ● Mixes technical and business aspects

114. ● Does not ﬁt the story telling ● Puts focus on model instead of behaviour ● Mixes technical and business aspects ● Can cause unnecessary contention

115. ● Does not ﬁt the story telling ● Puts focus on model instead of behaviour ● Mixes technical and business aspects ● Can cause unnecessary contention ● Can cause unnecessary complexity

116. ● Does not ﬁt the story telling ● Puts focus on model instead of behaviour ● Mixes technical and business aspects ● Can cause unnecessary contention ● Can cause unnecessary complexity ● Hard to refactor

117. Is there a better way to implement the command model?

118. Is there a better way to implement the command model? - F o c u s o n B e h a v i o r -

119. Lets restart from… story telling

120. Lets restart from… story telling

121. Lets restart from… story telling Decision Decision Decision Decision Decision

127. Focus on the decision

128. Focus on the decision Decision block = Message handler The message handler knows what it needs to make a decision

129. Focus on the decision Decision block = Message handler The message handler knows what it needs to make a decision

130. Event sourcing

131. Event sourcing Event sourcing provides a huge advantage because it decouples the persistence from the model needed for taking the decision The message handler can build on the ﬂy any model needed for taking the decision starting from the correct event stream

132. Event sourcing Event sourcing provides a huge advantage because it decouples the persistence from the model needed for taking the decision The message handler can build on the ﬂy any model needed for making the decision starting from the correct event stream

133. Event sourcing Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Event store

134. Event sourcing Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Update Course Capacity Command Event store

135. Event sourcing Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Update Course Capacity Command Event store

136. Event sourcing Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Update Course Capacity Command Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Command Handler Event store

137. Event sourcing Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Update Course Capacity Command Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Command Handler Event store

138. Event sourcing Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Update Course Capacity Command Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Command Handler Event store Course Capacity Changed

139. Event Store events = stream(AggregateIdentiﬁer id) events = stream(StreamQuery query)

142. Stream Query

143. Stream Query {"StreamQuery": { "DomainIdentifiers": [ { "course": "7d9b35b6-b46a-43bf-8e4c-eb7e6c3a487d" } ], "Types": [ "CourseCreated", "CourseCapacityChanged"] } }

147. The focus is on the Message Handler

148. The focus is on the Message Handler Less waste of resources No modelling phase More ﬂexibility

149. The focus is on the Message Handler Less waste of resources No upfront modelling required

150. The focus is on the Message Handler Less waste of resources No upfront modelling required More ﬂexibility

151. Concurrency Course Created Student Created …. Course Renamed …. Course Capacity Changed ….

152. Concurrency Update Course Capacity Command Rename Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed ….

153. Concurrency Update Course Capacity Command Rename Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The new name is different from prev one

154. Concurrency Update Course Capacity Command Rename Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The new name is different from prev one

155. Concurrency Update Course Capacity Command Rename Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Course Capacity Changed Course Renamed Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The new name is different from prev one

156. Concurrency Update Course Capacity Command Subscribe Student to Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed ….

157. Concurrency Update Course Capacity Command Subscribe Student to Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The number of current subscription is LOWER than the capacity (N)

158. Concurrency Update Course Capacity Command Subscribe Student to Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The number of current subscription is LOWER than the capacity (N)

159. Concurrency Update Course Capacity Command Subscribe Student to Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Course Capacity Changed Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The number of current subscription is LOWER than the capacity (N)

160. Concurrency Update Course Capacity Command Subscribe Student to Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Course Capacity Changed Student Subscribed to Course Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The number of current subscription is LOWER than the capacity (N)

161. Concurrency Update Course Capacity Command Subscribe Student to Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Course Capacity Changed Student Subscribed to Course Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The number of current subscription is LOWER than the capacity (N)

162. Event Store append(Event[] events) append(Event[] events, StreamQuery query, EventIdentiﬁer lastEvent)

165. Conditional append if (lastEventIdentifier(query) != lastEvent) { rejectAppend(); }

166. Conditional append if (lastEventIdentifier(query) != lastEvent) { rejectAppend(); }

167. Warranty of consistency The event(s) are appended only if the there is no other event matching the query that has appended after the lastEvent

168. Concurrency Update Course Capacity Command Subscribe Student to Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The number of current subscription is LOWER than the capacity (N) ...592

169. Concurrency Update Course Capacity Command Subscribe Student to Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Course Capacity Changed Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The number of current subscription is LOWER than the capacity (N) ...592 ...593 append(event, query, ...592)

170. Concurrency Update Course Capacity Command Subscribe Student to Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Course Capacity Changed Student Subscribed to Course Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The number of current subscription is LOWER than the capacity (N) ...592 ...593 append(event, query, ...592)

171. Concurrency Update Course Capacity Command Subscribe Student to Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Course Capacity Changed Student Subscribed to Course Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The number of current subscription is LOWER than the capacity (N) ...592 ...593 append(event, query, ...592) ...593 != ...592

172. Concurrency Update Course Capacity Command Subscribe Student to Course Command Course Created Student Created …. Course Renamed …. Course Capacity Changed …. Course Capacity Changed Student Subscribed to Course Decision based on the following business rules: ● The course exists ● The new capacity is different from prev Decision based on the following business rules: ● The course exists ● The number of current subscription is LOWER than the capacity (N) ...592 ...593 append(event, query, ...592) ...593 != ...592

173. Limited contention

174. Limited contention Before the contention boundaries were those of the aggregate... Now, the contention boundaries are those of the stream query

175. Limited contention Before the contention boundaries were those of the aggregate... Now, the contention boundaries are those of the stream query

176. Does not seem very artiﬁcial? Student Subscribed to Course Event Student Unsubscribed from Course Event Subscribe Student to Course Command Unsubscribe Student to Course Command Course Course Student Subscribed to Course Event Student Unsubscribed from Course Event Subscribe Student to Course Command Unsubscribe Student to Course Command Student Student

177. Course Created Student Created …. Course Renamed Course Capacity Changed …. Student Subscribed to Course Student Subscribed to Course

179. From the story-telling perspective Student Subscribed to Course Event Student Unsubscribed from Course Event Subscribe Student to Course Command Unsubscribe Student to Course Command

180. From the story-telling perspective Student Subscribed to Course Event Student Unsubscribed from Course Event Subscribe Student to Course Command Unsubscribe Student to Course Command Decision Decision

182. Course Created Student Created …. Course Renamed Course Capacity Changed …. Student Subscribed to Course Student Subscribed to Course Course Created Student Created …. Course Renamed Course Capacity Changed …. Student Subscribed to Course Student Subscribed to Course Pure Events

183. Course Created Student Created …. Course Renamed Course Capacity Changed …. Student Subscribed to Course Student Subscribed to Course Course Created Student Created …. Course Renamed Course Capacity Changed …. Student Subscribed to Course Student Subscribed to Course Pure Events Course: jdsj4 Student:gfh3j --- Course: jdsj4 Course: jdsj4 --- Course: jdsj4 Student: gfh3j Tags (Domain Identiﬁers)

184. Course Created Student Created …. Course Renamed Course Capacity Changed …. Student Subscribed to Course Student Subscribed to Course Pure Events Course: jdsj4 Student:gfh3j --- Course: jdsj4 Course: jdsj4 --- Course: jdsj4 Student: gfh3j Tags (Domain Identiﬁers)

185. Course Created Student Created …. Course Renamed Course Capacity Changed …. Student Subscribed to Course Course: jdsj4 Student:gfh3j --- Course: jdsj4 Course: jdsj4 --- Course: jdsj4 Student: gfh3j Pure Events Tags (Domain Identiﬁers)

186. Subscribe Student to Course Command

187. Subscribe Student to Course Command Decision based on the following business rules: - A course cannot accept more than N student - The student cannot join more than 10 courses

188. Student Subscribed to Course Event Subscribe Student to Course Command Decision based on the following business rules: - A course cannot accept more than N student - The student cannot join more than 10 courses

189. {"StreamQuery": { "DomainIdentifiers": [ { "course": "jdsj4..." }, { "student": "gfh3..." } ], "Types": [ "Course Created", "Student Created", "Course Capacity Changed", "Student Subscribed to Course", "Student Unsubscribed from Course"] }}

190. {"StreamQuery": { "DomainIdentifiers": [ { "course": "jdsj4..." }, { "student": "gfh3..." } ], "Types": [ "Course Created", "Student Created", "Course Capacity Changed", "Student Subscribed to Course", "Student Unsubscribed from Course"] }}

191. Subscribe Student to Course Command Decision based on the following business rules: - A course cannot accept more than N student - The student cannot join more than 10 courses Course Created Student Created …. Course Renamed Course Capacity Changed …. Course: jdsj4 Student:gfhl3 --- Course: jdsj4 Course: jdsj4 --- Pure Events Tags (Domain Identiﬁers)

192. Subscribe Student to Course Command Decision based on the following business rules: - A course cannot accept more than N student - The student cannot join more than 10 courses Course Created Student Created …. Course Renamed Course Capacity Changed …. Course: jdsj4 Student:gfhl3 --- Course: jdsj4 Course: jdsj4 --- Pure Events Tags (Domain Identiﬁers)

193. Student Subscribed to Course Event Subscribe Student to Course Command Decision based on the following business rules: - A course cannot accept more than N student - The student cannot join more than 10 courses Course Created Student Created …. Course Renamed Course Capacity Changed …. Course: jdsj4 Student:gfhl3 --- Course: jdsj4 Course: jdsj4 --- Pure Events Tags (Domain Identiﬁers) Student Subscribed to Course Course: jdsj4 Student: gfh3

194. Append Events with Domain Identiﬁers append(DomainEvent[] events) append(DomainEvent[] events, StreamQuery query, EventIdentiﬁer lastEvent)

195. Domain Event DomainEvent { Event event, DomainIdentiﬁers[] identiﬁers }

196. Domain Identiﬁer KEY: VALUE

197. Domain Identiﬁer KEY: VALUE The concept in the domain

198. Domain Identiﬁer KEY: VALUE The concept in the domain The unique instance identiﬁer

199. Domain Identiﬁer KEY: VALUE The concept in the domain The unique instance identiﬁer This is just an example, They can be anything, as far as they are unique inside the bounded context

200. Student Subscribed to Course Event Subscribe Student to Course Command Decision based on the following business rules: - A course cannot accept more than N students - The student cannot join more than 10 courses Course Created Student Created …. Course Renamed Course Capacity Changed …. Course: jdsj4 Student:gfh3j --- Course: jdsj4 Course: jdsj4 --- Pure Events Tags (Domain Identiﬁers) Student Subscribed to Course Course: jdsj4 Student: gfh3j

201. Student Subscribed to Course Event Subscribe Student to Course Command Decision based on the following business rules: - A course cannot accept more than N students - The student cannot join more than 10 courses Course Created Student Created …. Course Renamed Course Capacity Changed …. Course: jdsj4 Student:gfh3j --- Course: jdsj4 Course: jdsj4 --- Pure Events Tags (Domain Identiﬁers) Student Subscribed to Course Course: jdsj4 Student: gfh3j Course Fully Booked Event Course Fully Booked Course: jdsj4

202. append(DomainEvent[] events, StreamQuery query, EventIdentiﬁer lastEvent)

203. append(DomainEvent[] events, StreamQuery query, EventIdentifier lastEvent) [ Event event = Student subscribed to Course, DomainIdentifiers[] identifiers = [{course: "jdsj4..."}, {student:"gfh3..."}], Event event = Course Fully Booked, DomainIdentifiers[] identifiers = [{course: "jdsj4..."}] ]

204. append(DomainEvent[] events, StreamQuery query, EventIdentifier lastEvent) [ Event event = Student subscribed to Course, DomainIdentifiers[] identifiers = [{course: "jdsj4..."}, {student:"gfh3..."}], Event event = Course Fully Booked, DomainIdentifiers[] identifiers = [{course: "jdsj4..."}] ] DomainIdentifiers: [ {course: "jdsj4..."}, {student:"gfh3..."}], Types: [ "Course Created", "Student Created", "Course Capacity Changed", "Student Subscribed to Course", "Student Unsubscribed from Course"]}

205. append(DomainEvent[] events, StreamQuery query, EventIdentifier lastEvent) [ Event event = Student subscribed to Course, DomainIdentifiers[] identifiers = [{course: "jdsj4..."}, {student:"gfh3..."}], Event event = Course Fully Booked, DomainIdentifiers[] identifiers = [{course: "jdsj4..."}] ] DomainIdentifiers: [ {course: "jdsj4..."}, {student:"gfh3..."}], Types: [ "Course Created", "Student Created", "Course Capacity Changed", "Student Subscribed to Course", "Student Unsubscribed from Course"]} ...593

206. Pure events

207. Pure events An event does NOT belong to an aggregate An event is just a description of a fact that is important for the business An event can be related to one or multiple domain concepts, addressed by their Domain Identiﬁers

208. Pure events An event does NOT belong to an aggregate An event is just a description of a fact that is important for the business An event can be related to one or multiple domain concepts, addressed by their Domain Identiﬁers

209. Pure events An event does NOT belong to an aggregate An event is just a description of a fact that is important for the business An event can be related to one or multiple domain concepts addressed by their Domain Identiﬁers

210. Less complexity

211. Less complexity No owner of the event The business decision can easily involve several domain concepts The decision is taken in one place

214. Saga Subscribe Student to Course Command Subscribe Student to Course Command Subscribe Student to Course Command Student Subscribed Course Event Student Course revert Unsubscribe Student to Course Command Student Unsubscribed Course Event Student 1 1 2 3

215. More ﬂexibility Event sourcing provides a huge advantage because it decouples the persistence from the model needed for taking the decision Refactoring ● Change the StreamQuery ● Add/Remove Domain Identiﬁers

216. More ﬂexibility Event sourcing provides a huge advantage because it decouples the persistence from the model needed for taking the decision Refactoring ● Change the StreamQuery

217. More ﬂexibility Event sourcing provides a huge advantage because it decouples the persistence from the model needed for taking the decision Refactoring ● Change the StreamQuery ● Add/Remove Domain Identiﬁers

219. Dynamic Consistency Boundary - aka DCB

220. Dynamic Consistency Boundary - aka DCB ● Perfect match with story telling

221. Dynamic Consistency Boundary - aka DCB ● Perfect match with story telling ● Focus on behaviour instead of model

222. Dynamic Consistency Boundary - aka DCB ● Perfect match with story telling ● Focus on behaviour instead of model ● Less contention

223. Dynamic Consistency Boundary - aka DCB ● Perfect match with story telling ● Focus on behaviour instead of model ● Less contention ● Less complexity

224. Dynamic Consistency Boundary - aka DCB ● Perfect match with story telling ● Focus on behaviour instead of model ● Less contention ● Less complexity ● Simpler to refactor

225. The aggregate is dead Long live the aggregate

228. There is no pattern that can replace common sense.

229. @_sara_p_ Sara Pellegrini @MilanSavic14 Milan Savic

The aggregate is dead! Long live the aggregate! - SpringIO.pdf

The aggregate is dead! Long live the aggregate! - SpringIO.pdf

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The aggregate is dead! Long live the aggregate! - SpringIO.pdf