The aggregate is dead! Long live the aggregate! - SpringIO.pdf
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https://2023.springio.net/sessions/the-aggregate-is-dead-long-live-the-aggregate/ SARA PELLEGRINI - AXONIQ MILAN SAVIC - AXONIQ DDD’s definition of Aggregate may seem somewhat confusing - “An aggregate is a cluster of associated objects that we treat as a unit for the purpose of data changes.” Okay, let’s try to clarify - “You should consider your aggregate as a unit of consistency in your Domain.”. That doesn’t help either. As a matter of fact, while modeling our systems, we tend to group together events related to the same domain concept; we tend to define groups based on the nouns we find inside our events’ name: saying “this is our aggregate!”. According to the aggregate definition, we should instead ignore these nouns, and put together the data that change together. Easier said than done: in the modeling phase it is easy to make mistakes trying to identify the boundaries of our aggregates based on this rule. If we opt for saving the state of our aggregate as a series of events, we are in big trouble - any (serious) refactoring of the aggregate structure becomes close to impossible. The reason for this trouble is that we have to make a decision in the design phase for which we cannot be lenient. We are basically married to this decision forever. Due to the aforementioned reasons (and many others), people struggle with the Aggregate pattern. Some even say it is unnecessary, we are one of those. Let’s see whether we can model our business constraints without aggregates. Could we be more relaxed when consistency is in question? Join us to discover how!
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The aggregate is dead! Long live the aggregate! - SpringIO.pdf
- 1. The aggregate is dead! Long live 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
- 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
- 21. Course Created Event Student Subscribed to Course Event Student Unsubscribed from Course 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
- 55. The larger the Aggregate the greater the contention
- 56. The boundary of consistency is also the boundary of concurrency
- 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 *
- 60. Concurrent command execution Update Course Capacity Command Rename Course Command <<Aggregate Root>> Course Subscription * <<Aggregate Root>> Course Subscription *
- 61. Concurrent command execution Update Course Capacity Command Rename Course Command <<Aggregate Root>> Course Subscription * <<Aggregate Root>> Course Subscription *
- 62. Concurrent command execution Update Course Capacity Command Rename Course Command <<Aggregate Root>> Course Subscription * <<Aggregate Root>> Course Subscription *
- 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 - ???
- 73. What if model changes… Now what??? State Persisted Aggregates - Script Event Sourced Aggregates - ???
- 74. What if model changes… Now what??? State Persisted Aggregates - Script Event Sourced Aggregates - ???
- 75. 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
- 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
- 122. Lets restart from… story telling Decision Decision Decision Decision Decision
- 123. Lets restart from… story telling Decision Decision Decision Decision Decision
- 124. Lets restart from… story telling Decision Decision Decision Decision Decision
- 125. Lets restart from… story telling Decision Decision Decision Decision Decision
- 126. 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
- 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)
- 140. Event Store events = stream(AggregateIdentifier id) events = stream(StreamQuery query)
- 141. 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"] } }
- 144. Stream Query {"StreamQuery": { "DomainIdentifiers": [ { "course": "7d9b35b6-b46a-43bf-8e4c-eb7e6c3a487d" } ], "Types": [ "CourseCreated", "CourseCapacityChanged"] } }
- 145. Stream Query {"StreamQuery": { "DomainIdentifiers": [ { "course": "7d9b35b6-b46a-43bf-8e4c-eb7e6c3a487d" } ], "Types": [ "CourseCreated", "CourseCapacityChanged"] } }
- 146. 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
- 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
- 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)
- 163. Event Store append(Event[] events) append(Event[] events, StreamQuery query, EventIdentifier lastEvent)
- 164. 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
- 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)
- 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 }
- 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
- 212. Less complexity No owner of the event The business decision can easily involve several domain concepts The decision is taken in one place
- 213. 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.