DDD & REST — Domain-Driven APIs for the web

Slides of the talk I gave at DDD user group in Berlin.

@springcentral

Transcript

1. DDD & REST Domain-Driven APIs for the web / olivergierke Oliver Gierke ogierke@pivotal.io
3. Background 3
4. 4 Spring Data Repositories &
 Aggregates Spring HATEOAS Hypermedia
 for Spring MVC Spring Data REST
5. REST ≠ 
 CRUD via HTTP 5
6. What does it take to bridge the worlds of DDD & REST? “ 6
8. 8 http://www.infoq.com/minibooks/domain-driven-design-quickly
11. Implementing Domain-Driven Design 10
12. Value objects 11
13. Stringly typed code 12 public class Customer { private Long id; private String firstname, lastname, email; … }
14. Stringly typed code 13 public class SomeService { public void createUser(String firstname,
 String lastname, String email) { … } }
15. 14 public class Customer { private Long id; private Firstname firstname; private Lastname lastname; private EmailAddress emailAddress; … }
16. Value Objects are a
 PITA to build in
 some languages. 15
17. Still, they’re worth it. 16 See „Power Use of Value Objects in DDD“ by Dan Bergh Johnsson.
18. Lombok — putting the spice back into Java. 17
19. 18 @Value public class Customer { UUID id = UUID.randomUUID(); Firstname firstname; Lastname lastname; EmailAddress email; @Value static class EmailAddress { String value; } }
20. AutoValue 19 Project website on GitHub.
21. Key opponents: Mapping libraries
 that need to
 (de)serialize them. 20
22. Entities & Repositories 21
23. 22 Order LineItem Product Invoice Customer Payment Address Email
24. 22 Order LineItem Product Invoice Customer Payment Address Email
25. Entity +
 Repository = 
 Aggregate 23
26. Aggregates form nice representation boundaries. 24
27. Aggregates become
 the key things
 to refer to. 25
28. Don’t get trapped by datastore thinking. 26
29. Try to avoid 
 bi-directional relationships. 27
30. Bounded Context 28
31. Order LineItem Product Invoice Customer Payment Address
32. 30 Shipping Accounting Catalog Orders User
 Registration
33. 30 Shipping Accounting Catalog Orders User
 Registration Accounting Payment information Billing Address Shipping Shipping address Customer Product
34. Domain Events 31
35. 32 Level 0: No events at all
36. 32 Level 0: No events at all Level 1: Explicit operations
37. If you’re calling two setters in a row, you’re missing a concept. 33
38. 34 Level 0: No events at all Level 1: Explicit operations Level 2: Some operations as events
39. Domain events as
 state transitions. 35
40. Expose important
 events to interested parties via feeds. 36
41. 37 Level 0: No events at all Level 1: Explicit operations Level 2: Some operations as events Level 3: Event Sourcing
42. REST 38
43. Representation design matters 39
44. Aggregates Identifiable
 Referable
 Scope of consistency 40
45. Resources Identifiable
 Referable
 Scope of consistency 41
46. Hypermedia 42
47. Serving data and navigation information
 at the same time. 43
48. Trading domain knowledge with protocol complexity in clients. 44
49. Reducing decisions in clients to whether a
 link is present or not. 45
50. Prefer explicit 
 state transitions over poking at your resources using PATCH. 46
51. Translate domain concepts into web- appropriate ones. 47
52. 48 Aggregate Root / Repository Collection / Item Resources IDs URIs @Version ETags Last Modified Property Last Modified Header Relations Links
53. RESTBucks payment expected preparing cancelled ready completed 1 2 3 4 5 6
54. Method URI Action Step POST /orders Create new order 1 POST/PATCH /orders/{id} Update the order (only if "payment expected") 2 DELETE /orders/{id} Cancel order (only if "payment expected") 3 PUT /orders/{id}/payment Pay order (only if "payment expected") 4 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
55. 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
56. 52 GET /orders { „_links“ : { „cancel“ : { „href“ : … }, … „createdDate“ : …, „status“ : „Payment expected“ … }
57. 53 GET /orders { „_links“ : { „cancel“ : { „href“ : … }, … „createdDate“ : …, „status“ : „Payment expected“ … }
58. 54 “Internationalize
 all user facing text.
59. Aaaargh! 55
60. 56 GET /orders { „_links“ : { „cancel“ : { „href“ : … }, … „createdDate“ : …, „status“ : „Payment expected“ … }
61. Spring RESTBucks 57
62. Web Service Repository - Orders Spring Data Spring Data
 REST Payment Spring Data Manual
 implementation Manual
 implementation
63. JacksonCustomizations Externalize tweaks to the general JSON design 59
64. Spring Data REST
 for the CRUDdy parts. 60
65. ResourceProcessor To conditionally sneak links into the default representation. 61
66. Resources 62 Spring RESTBucks
 https://github.com/olivergierke/spring-restbucks Benefits of Hypermedia APIs
 http://olivergierke.de/2016/04/benefits-of-hypermedia/index.html
67. Questions? 63