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© 2014 SpringOne 2GX. All rights reserved. Do not distribute without permission. DOMAIN-DRIVEN DESIGN / OLIVERGIERKE ƻ [email protected] GRUNDLEGENDES FÜR MICROSERVICES

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4 http://www.infoq.com/minibooks/domain-driven-design-quickly

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Microservices ♥
 Domain-Driven Design 5 Slides and video by Michael Plöd.

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Implementing Domain-Driven Design 7

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Value objects 8

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Stringly typed code 9 public class Customer { private Long id; private String firstname, lastname, email; … }

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Stringly typed code 10 public class SomeService { public void createUser(String firstname,
 String lastname, String email) { … } }

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11 public class Customer { private Long id; private Firstname firstname; private Lastname lastname; private EmailAddress emailAddress; … }

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Value Objects are a
 PITA to build in
 some languages. 12

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Still, they’re worth it. 13 See „Power Use of Value Objects in DDD“ by Dan Bergh Johnsson.

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Lombok — putting the spice back into Java. 14

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15 @Value public class Customer { UUID id = UUID.randomUUID(); Firstname firstname; Lastname lastname; EmailAddress email; @Value static class EmailAddress { String value; } }

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AutoValue 16 Project website on GitHub.

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Key opponents: Mapping libraries
 that need to
 (de)serialize them. 17

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Entities & Aggregates 18

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Persistence technology
 VS.
 Domain model 19

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Challenges with JPA:
 
 Value objects as @Entity
 Flat relationships 20

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21 Order LineItem Product Invoice Customer Payment Address Email

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21 Order LineItem Product Invoice Customer Payment Address Email

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Repositories turn
 an entity into an aggregate root. 22

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23 Order LineItem Product Invoice Customer Payment Address Email

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Bounded Context 24

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Order LineItem Product Invoice Customer Payment Address

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26 Shipping Accounting Catalog Orders User
 Registration

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26 Shipping Accounting Catalog Orders User
 Registration Accounting Payment information Billing Address Shipping Shipping address Customer

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26 Shipping Accounting Catalog Orders User
 Registration Accounting Payment information Billing Address Shipping Shipping address Customer Product

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Domain-Driven Design & Monoliths 27

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Avoid technologies that get in your way. 28

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How to enforce
 context boundaries? 29

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What about
 consistency? 30

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References between Bounded Contexts? 31

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Domain Events 32

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33 Level 0: No events at all

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33 Level 0: No events at all Level 1: Explicit operations

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If you’re calling two setters in a row, you’re missing a concept. 34

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35 Level 0: No events at all Level 1: Explicit operations

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35 Level 0: No events at all Level 1: Explicit operations Level 2: Some operations as events

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State transitions
 become domain
 events. 36

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37 Level 0: No events at all Level 1: Explicit operations Level 2: Some operations as events

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37 Level 0: No events at all Level 1: Explicit operations Level 2: Some operations as events Level 3: Event Sourcing

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Domain-Driven Design & Microservices 38

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Bounded contexts 
 define system
 boundaries. 39

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40 Shipping Accounting Catalog Orders User
 Registration Accounting Payment information Billing Address Shipping Shipping address Customer Product

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41 Shipping Accounting Catalog Orders User
 Registration Accounting Shipping

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42 Shipping Accounting Catalog Orders User
 Registration Accounting Shipping HTTP Messaging

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Architecture is less
 likely to deteriorate
 as it’s harder to
 violate boundaries. 43

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Restructuring
 service boundaries
 is much harder. 44

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Inter-Service communication
 becomes remote
 communication. 45

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Accept and embrace eventual consistency between services. 46

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Domain Events 47

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REST & Messaging 48

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Domain events
 become state
 transitions. 49

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Hypermedia for state transition and explicit events. 50

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Thanks! 51