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DDD & REST Domain-Driven APIs for the web Oliver Gierke / - - PowerPoint PPT Presentation
DDD & REST Domain-Driven APIs for the web Oliver Gierke / - - PowerPoint PPT Presentation
DDD & REST Domain-Driven APIs for the web Oliver Gierke / olivergierke 2 Background 3 Spring Data REST Spring Data Spring HATEOAS Repositories & Hypermedia Aggregates for Spring MVC 4 REST CRUD via HTTP 5
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Background
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Spring Data
Repositories & AggregatesSpring HATEOAS
Hypermedia for Spring MVCSpring Data REST
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REST ≠ CRUD via HTTP
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What does it take to bridge the worlds of DDD & REST?
“
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Value objects
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Value Objects are a PITA to build in some languages.
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Still, they’re worth it.
10 See „Power Use of V alue Objects in DDD“ by Dan Bergh Johnsson. SLIDE 12
Lombok — putting the spice back into Java.
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Key opponents: Mapping libraries that need to (de)serialize them.
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Entities & Repositories
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Customer Payment Address Email
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Invoice Customer Payment Address Email
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Order LineItem Invoice Customer Payment Address Email
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Order LineItem Product Invoice Customer Payment Address Email
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Order LineItem Product Invoice Customer Payment Address Email
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Entity + Repository = Aggregate
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Aggregates form nice representation boundaries.
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Aggregates become the key things to refer to.
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Don’t get trapped by datastore thinking.
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Try to avoid bi-directional relationships.
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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
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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
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Domain events as state transitions.
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Expose important events 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
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REST
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Representation design matters
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Aggregates
Identifiable Referable Scope of consistency
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Resources
Identifiable Referable Scope of consistency
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Hypermedia
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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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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
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RESTBucks
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RESTBucks
payment expected preparing cancelled ready completed 1 2 3 4 5 6 SLIDE 47 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 Method Resource type Action Step POST
- rders
- rder
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Spring RESTBucks
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- Orders
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JacksonCustomizations Externalize tweaks to the general JSON design
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Spring Data REST for the CRUDdy parts.
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ResourceProcessor To conditionally sneak links into the default representation.
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Code
46 Spring RESTBucks - https://github.com/olivergierke/spring-restbucks SLIDE 55
Questions?
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