DDD & REST Domain Driven Apis for the Web
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Unless otherwise indicated, these slides are © 2013-2016 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/ DDD & REST Domain-Driven APIs for the web Oliver Gierke / olivergierke [email protected]
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Transcript of DDD & REST Domain Driven Apis for the Web
Unless o therw ise ind ica ted , these s l ides are © 2013-2016 P ivo ta l So f tware , Inc . and l i censed under a Creat ive Commons At t r ibu t ion-NonCommerc ia l l i cense: h t tp : / / c rea t ivecommons.org / l i censes /by-nc /3 .0 /
DDD & RESTDomain-Driven APIs for the web
Oliver Gierke !/" olivergierke
Background
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Spring Data
Repositories &Aggregates
Spring HATEOAS
Hypermediafor Spring MVC
Spring Data REST
When designing REST APIs, what can we learn from DDD?“
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What does it take to bridge the worlds of DDD & REST?“
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http://www.infoq.com/minibooks/domain-driven-design-quickly
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Implementing Domain-Driven
Design10
Value objects
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Stringly typed code12
public class Customer {
private Long id;private String firstname, lastname, email;
…}
Stringly typed code13
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 a PITA 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 & Repositories
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Order
LineItem
Product
Invoice
CustomerPayment Address
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Order
LineItem
Product
Invoice
CustomerPayment Address
Entity +Repository =
Aggregate
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Aggregates.Scopes of consistency.
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Order
LineItem
Product
Invoice
CustomerPayment Address
Aggregates.The key things
to refer to.
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Order
LineItem
Product
Invoice
CustomerPayment Address
Don’t get trapped by datastore thinking.
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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
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Shipping
AccountingCatalog
Orders
UserRegistration
Accounting Payment information
Billing Address
Shipping
Shipping address
Customer
Product
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
Domain events asstate transitions.
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Expose importantevents to interested
parties via feeds.
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Level 0: No events at all
Level 1: Explicit operations
Level 2: Some operations as events
Level 3: Event Sourcing
REST
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REST ≠ CRUD via HTTP
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Representation design matters
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Value objects need custom
serializers.
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Aggregates IdentifiableReferable
Scope of consistency
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Resources IdentifiableReferable
Scope of consistency
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Serving data and navigation information
at the same time.
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Trading domain knowledge with protocol
complexity in clients.
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Amount of domain knowledge in the client
Amount of protocol knowledge in the client
Coupling to the server
Non-hypermediabased systems
Hypermediabased systems
API evolvability is key in a system of systems
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GET /orders
{ „_links“ : { „cancel“ : { „href“ : … }, … „createdDate“ : …, „status“ : „Payment expected“ … }
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GET /orders
{ „_links“ : { „cancel“ : { „href“ : … }, … „createdDate“ : …, „status“ : „Payment expected“ … }
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“ Internationalizeall user facing text.
Aaaargh!
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GET /orders
{ „_links“ : { „cancel“ : { „href“ : … }, … „createdDate“ : …, „status“ : „Payment expected“ … }
Reducing decisions in clients to whether a
link is present or not.
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Prefer explicit state transitions over
poking at your resources using PATCH.
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Translate domain concepts into web-appropriate ones.
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Aggregate Root / Repository
Collection / Item Resources
IDs URIs
@Version ETags
Last Modified Property
Last Modified Header
Relations Links
RESTBuckspayment expected
preparing
cancelled
ready completed
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Method URI Action Step
POST /orders Create new order 1
POST/PATCH /orders/{id} Update the order (only if "payment expected")
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DELETE /orders/{id} Cancel order (only if "payment expected")
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PUT /orders/{id}/payment Pay order (only if "payment expected")
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Barista preparing the order
GET /orders/{id} Poll order state 5
GET /orders/{id}/receipt Access receipt
DELETE /orders/{id}/receipt Conclude the order process 6
Method Resource type Action Step
POST orders Create new order 1
POST/PATCH update Update the order 2
DELETE cancel Cancel order 3
PUT payment Pay order 4
Barista preparing the order
GET order Poll order state 5
GET receipt Access receipt
DELETE receipt Conclude the order process 6
Spring RESTBucks
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Web
Service
Repository
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Orders
Spring Data
Spring DataREST
Payment
Spring Data
Manualimplementation
Manualimplementation
Resources
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Spring RESTBuckshttps://github.com/olivergierke/spring-restbucks
Benefits of Hypermedia APIshttp://olivergierke.de/2016/04/benefits-of-hypermedia/index.html
Questions?
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