Domain-Driven Design and CQRS Xebia ITR on Command Query - - PowerPoint PPT Presentation

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Domain-Driven Design and CQRS Xebia ITR on Command Query - - PowerPoint PPT Presentation

Sep 07, 2022 403 likes •794 views

Domain-Driven Design and CQRS Xebia ITR on Command Query Responsibility Separation Sjors Grijpink and Erik Rozendaal DDD Eric Evans, Domain- Driven Design, 2004 Key concepts Ubiquitous Language Value Object, Entity

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Domain-Driven Design and CQRS

Xebia ITR on Command Query Responsibility Separation Sjors Grijpink and Erik Rozendaal

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SLIDE 2

DDD

  • Eric Evans, Domain-

Driven Design, 2004

  • Key concepts
  • Ubiquitous Language
  • Value Object, Entity
  • Aggregate
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Ubiquitous Language

  • Language shared between domain experts

and developers

  • No need for error-prone translation
  • Maps directly to domain implementation
  • Implementation should be free of

“technical” terms

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Value Object

  • No conceptual identity
  • Describe characteristic of a thing
  • Usually immutable
  • Examples: Address, Money, ...
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SLIDE 5

Entity

  • Something with a unique identity
  • Identity does not change when any of its

attributes change

  • Examples: Customer, Order, ...
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Aggregate

  • Group of Entities &

Value Objects

  • One entity within the aggregate is the

aggregate root

  • All access to the objects inside go through

the root entity

  • Aggregates are consistency boundaries
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SLIDE 7

Lottery

  • Two aggregate roots
  • Lottery
  • Customer

Lottery Ticket Customer

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3 Tier

  • Presentation layer is

denormalized

  • Domain is behavioral
  • Transactional database

is normalized

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SLIDE 9

“A single model cannot be appropriate for reporting, searching, and transactional behaviors.” - Greg Young

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Purchase Lottery Ticket

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Purchase Lottery Ticket Lottery Ticket Purchased

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Purchase Lottery Ticket Lottery Ticket Purchased Find Lottery Tickets for Customer

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All state changes are represented by Domain Events

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SLIDE 19

Domain

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Reporting

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Packages

Domain Presentation Reporting Commands Events Queries

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Packages

Domain Presentation Reporting Commands Events Queries Shared

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SLIDE 23

Packages

Domain Presentation Reporting Commands Events Queries Shared CQRS framework

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Exercise 1

  • Implement “Create Customer”
  • Test that customers are listed on the

screen

  • Test that customers cannot be created with

an initial payment of less than 10.00

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Exercise 2

  • Implement “Purchase Lottery Ticket”
  • Ticket should be listed
  • Customer’s balance should be updated
  • Don’t forget to check the customer’s

account balance

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Benefits

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SLIDE 27

Benefits

  • Fully encapsulated domain that only exposes behavior
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SLIDE 28

Benefits

  • Fully encapsulated domain that only exposes behavior
  • Queries do not use the domain model
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SLIDE 29

Benefits

  • Fully encapsulated domain that only exposes behavior
  • Queries do not use the domain model
  • No object-relational impedance mismatch
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SLIDE 30

Benefits

  • Fully encapsulated domain that only exposes behavior
  • Queries do not use the domain model
  • No object-relational impedance mismatch
  • Bullet-proof auditing and historical tracing
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Benefits

  • Fully encapsulated domain that only exposes behavior
  • Queries do not use the domain model
  • No object-relational impedance mismatch
  • Bullet-proof auditing and historical tracing
  • Easy integration with external systems
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Benefits

  • Fully encapsulated domain that only exposes behavior
  • Queries do not use the domain model
  • No object-relational impedance mismatch
  • Bullet-proof auditing and historical tracing
  • Easy integration with external systems
  • Performance and scalability
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Benefits

  • Fully encapsulated domain that only exposes behavior
  • Queries do not use the domain model
  • No object-relational impedance mismatch
  • Bullet-proof auditing and historical tracing
  • Easy integration with external systems
  • Performance and scalability
  • Testability
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SLIDE 34

Bounded Context

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Advanced Topics

  • Snapshots
  • Command-event conflict resolution
  • Eventual consistency
  • Transaction-aware repository
  • ...
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Snapshot

Event Store 4 snapshot 3 2 1 Repository save load

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The End

  • Eric Evans, Domain-Driven Design
  • Greg

Young, Unshackle Your Domain