DDD & REST — Domain-Driven APIs for the web

Slide 1

Slide 1 text

DDD & REST Domain-Driven APIs for the web / olivergierke Oliver Gierke

Slide 2

Slide 2 text

Slide 3

Slide 3 text

Background 3

Slide 4

Slide 4 text

4 Spring Data Repositories &  Aggregates Spring HATEOAS Hypermedia  for Spring MVC Spring Data REST

Slide 5

Slide 5 text

REST ≠   CRUD via HTTP 5

Slide 6

Slide 6 text

What does it take to bridge the worlds of DDD & REST? “

Slide 7

Slide 7 text

Slide 8

Slide 8 text

Slide 9

Slide 9 text

Value objects 8

Slide 10

Slide 10 text

Value Objects are a  PITA to build in  some languages. 9

Slide 11

Slide 11 text

Still, they’re worth it. 10 See „Power Use of Value Objects in DDD“ by Dan Bergh Johnsson.

Slide 12

Slide 12 text

Lombok — putting the spice back into Java. 11

Slide 13

Slide 13 text

Key opponents: Mapping libraries  that need to  (de)serialize them. 12

Slide 14

Slide 14 text

Entities & Repositories 13

Slide 15

Slide 15 text

Slide 16

Slide 16 text

14 Customer Payment Address Email

Slide 17

Slide 17 text

14 Invoice Customer Payment Address Email

Slide 18

Slide 18 text

14 Order LineItem Invoice Customer Payment Address Email

Slide 19

Slide 19 text

14 Order LineItem Product Invoice Customer Payment Address Email

Slide 20

Slide 20 text

14 Order LineItem Product Invoice Customer Payment Address Email

Slide 21

Slide 21 text

Entity +  Repository =   Aggregate 15

Slide 22

Slide 22 text

Aggregates form nice representation boundaries. 16

Slide 23

Slide 23 text

Aggregates become  the key things  to refer to. 17

Slide 24

Slide 24 text

Don’t get trapped by datastore thinking. 18

Slide 25

Slide 25 text

Try to avoid   bi-directional relationships. 19

Slide 26

Slide 26 text

Domain Events 20

Slide 27

Slide 27 text

21 Level 0: No events at all

Slide 28

Slide 28 text

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

Slide 29

Slide 29 text

If you’re calling two setters in a row, you’re missing a concept. 22

Slide 30

Slide 30 text

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

Slide 31

Slide 31 text

Domain events as  state transitions. 24

Slide 32

Slide 32 text

Expose important  events to interested parties via feeds. 25

Slide 33

Slide 33 text

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

Slide 34

Slide 34 text

REST 27

Slide 35

Slide 35 text

Representation design matters 28

Slide 36

Slide 36 text

Aggregates Identiﬁable  Referable  Scope of consistency 29

Slide 37

Slide 37 text

Resources Identiﬁable  Referable  Scope of consistency 30

Slide 38

Slide 38 text

Hypermedia 31

Slide 39

Slide 39 text

Serving data and navigation information  at the same time. 32

Slide 40

Slide 40 text

Trading domain knowledge with protocol complexity in clients. 33

Slide 41

Slide 41 text

Reducing decisions in clients to whether a  link is present or not. 34

Slide 42

Slide 42 text

Prefer explicit   state transitions over poking at your resources using PATCH. 35

Slide 43

Slide 43 text

Translate domain concepts into web- appropriate ones. 36

Slide 44

Slide 44 text

37 Aggregate Root / Repository Collection / Item Resources IDs URIs @Version ETags Last Modified Property Last Modified Header Relations Links

Slide 45

Slide 45 text

RESTBucks

Slide 46

Slide 46 text

RESTBucks payment expected preparing cancelled ready completed 1 2 3 4 5 6

Slide 47

Slide 47 text

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

Slide 48

Slide 48 text

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

Slide 49

Slide 49 text

Spring RESTBucks 41

Slide 50

Slide 50 text

Web Service Repository - Orders Spring Data Spring Data  REST Payment Spring Data Manual  implementation Manual  implementation

Slide 51

Slide 51 text

JacksonCustomizations Externalize tweaks to the general JSON design 43

Slide 52

Slide 52 text

Spring Data REST  for the CRUDdy parts. 44

Slide 53

Slide 53 text

ResourceProcessor To conditionally sneak links into the default representation. 45