fundamental domain-driven design - java forum stuttgart · . ... see „power use of value objects...
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DOMAIN-DRIVEN DESIGN! / " OLIVERGIERKE
FUNDAMENTAL
FOR MICROSERVICES
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http://www.infoq.com/minibooks/domain-driven-design-quickly
Microservices ♥Domain-Driven Design
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11:10 — Beethoven Saal
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Implementing Domain-Driven
Design7
Value objects
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Stringly typed code9
public class Customer {
private Long id;private String firstname, lastname, email;
…}
Stringly typed code10
public class SomeService {
public void createUser(String firstname, String lastname, String email) {
…}
}
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public class Customer {
private Long id;private Firstname firstname;private Lastname lastname;private EmailAddress emailAddress;
…}
Value Objects are aPITA to build in
some languages.
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Still, they’re worth it.
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See „Power Use of Value Objects in DDD“ by Dan Bergh Johnsson.
Lombok — putting the spice back into Java.
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@Valuepublic class Customer {
UUID id = UUID.randomUUID();Firstname firstname;Lastname lastname;EmailAddress email;
@Valuestatic class EmailAddress {String value;
}}
AutoValue
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Project website on GitHub.
Entities & Aggregates
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Order
LineItem
Product
Invoice
CustomerPayment Address
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Order
LineItem
Product
Invoice
CustomerPayment Address
Persistence technologyVS.
Domain model
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Aggregate =Entity + Repository
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Order
LineItem
Product
Invoice
CustomerPayment Address
Bounded Context
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Order
LineItem
Product
Invoice
CustomerPayment Address
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Shipping
AccountingCatalog
Orders
UserRegistration
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Shipping
AccountingCatalog
Orders
UserRegistration
Accounting Payment information
Billing Address
Shipping
Shipping address
Customer
Product
Domain-Driven Design &
Monoliths25
Avoid technologies that get in your way.
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How to enforcecontext boundaries?
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What aboutconsistency?
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References between Bounded Contexts?
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Domain Events
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Level 0: No events at all
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Level 0: No events at all
Level 1: Explicit operations
If you’re calling two setters in a row, you’re
missing a concept.
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Level 0: No events at all
Level 1: Explicit operations
Level 2: Some operations as events
State transitionsbecome domain
events.
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Level 0: No events at all
Level 1: Explicit operations
Level 2: Some operations as events
Level 3: Event Sourcing
Domain-Driven Design &
Microservices36
Bounded contexts define systemboundaries.
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Shipping
AccountingCatalog
Orders
UserRegistration
Accounting Payment information
Billing Address
Shipping
Shipping address
Customer
Product
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Shipping
AccountingCatalog
Orders
UserRegistration
Accounting
Shipping
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Shipping
AccountingCatalog
Orders
UserRegistration
Accounting
Shipping
HTTP
Messaging
Architecture is lesslikely to deteriorate
as it’s harder toviolate boundaries.
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Restructuringservice boundaries
is much harder.
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Inter-Service communicationbecomes remotecommunication.
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Accept and embrace eventual consistency
between services.
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Domain Events
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REST & Messaging
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Domain eventsbecome state
transitions.
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Hypermedia for state transition and explicit
events.
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Thanks!
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