LinkRest (http://linkrest.io) is a small HTTP-based protocol and a Java framework that rethinks how REST APIs should be built and consumed. It turns each API endpoint into a graph query engine, giving the client full control over the shape and contents of the requested data sets, while the server controls query strategy and security. The talk will start with the easy parts – how to reuse an existing Apache Cayenne ORM model for the REST service and write simple Java one-liners to get it up and running. Then we will delve into alternative backends, graph access security and parallel data processing.

1. RESTful Data Services with
LinkRest
by Andrus Adamchik
@andrus_a
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2. About Me
• Open source developer: ORM, DI, REST, no-container
• Member and ex-VP of the Apache Software Foundation
• Run a company called ObjectStyle
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3. I Love REST
• HTTP is a clean and universal protocol
• Near-infinite scalability
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4. Hi! I am a REST API Client
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5. Domain Model
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6. Domain Model Aggregates
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7. Aggregate-Centric REST API
• An aggregate handled by a single REST resource
• Decoupling / encapsulation
• Assumes "normal" use cases don't cross aggregate boundaries
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8. Problem #1: Too Much Data
curl -i
'https://api.github.com/repos/nhl/link-rest/issues?state=all'
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• Returns 126K JSON
• We need 3K ("title", "number", "id")

9. Problem #2: Too Little Data
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curl -i
'https://api.github.com/repos/nhl/link-rest/issues?state=all'
{
// O(N) problem:
// for each issue fetch events via a separate REST call
"events_url" : "https://api.github.com/.../issues/207/events"
...
}

10. LinkRest
• From aggregates to graphs
• Client decides on request shape / size
• One size fits all
• Reuse existing (ORM) models
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11. Demo: Hockey Schedule App
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12. LinkRest Protocol
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13. 13
Shaping Response
{"id":2016020001}
?include=id
{"id":2016020001,"homeTeam":{"name":"Rangers"}}
?include=id&include=homeTeam.name
?exclude=arena&exclude=dateTime
{"id":2016020001,"inProgress":false}

14. 14
?cayenneExp=inProgress=true
SELECT t0.* FROM game t0 WHERE t0.in_progress = 1
SELECT t0.* FROM game t0 JOIN team t1 ON (t0.home_team_id = t1.id) WHERE
t1.name LIKE 'New York%'
?cayenneExp=["homeTeam.name like $t","New York%"]
Filtering

15. 15
?sort=dateTime
SELECT t0.* FROM game t0 ORDER BY t0.date_time
SELECT t0.* FROM game t0 ORDER BY t0.date_time DESC
?sort=dateTime&dir=DESC
SELECT t0.* FROM game t0 JOIN team t1 ON (t0.home_team_id = t1.id) ORDER BY
t0.in_progress, t1.name DESC
?sort=[{"property":"inProgress"},{"property":"homeTeam.name","direction":"DESC"}]
Sorting

16. 16
?start=2
{"data":[ /*objects 2..9*/ ], "total":10}
Pagination (for a list of 10 objects)
{"data":[ /*objects 0..4*/ ], "total":10}
?limit=5
{"data":[ /*objects 2..6*/ ], "total":10}
?start=2&limit=5

17. 17
?include={"path":"homeGames","cayenneExp":"arena = 'Madison Square
Garden'","sort":"dateTime"}&include=homeGames.id
{
"homeGames": [
{ "id": 2016020075 },
{ "id": 2016020790 }
]
}
Advanced Include

18. Constraints API
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• Prevents DOS attacks
• Fine-grained attribute security
ConstraintsBuilder<Team> tc = Constraint.idAndAttributes(Team.class);
ConstraintsBuilder<Game> gc = Constraint.idAndAttributes(Game.class)
.path("homeTeam", tc)
.path("visitingTeam", tc);
return LinkRest.select(Game.class, configuration)
.uri(uri)
.constraint(gc)
.get();

19. Demo: Modifying Data
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20. Create/Update Flavors
• create(..)
• update(..)
• createOrUpdate(..)
• idempotentCreateOrUpdate(..)
• idempotentFullSync(..)
• delete(..)
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21. Demo: Live Game Events App
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22. Takeaway
• POJOs can be exposed via LinkRest using annotations
• Custom backend is plugged in as a "stage listener"
• "include" / "exclude" / "limit" supported automatically
• Other protocol features are up to the backend to implement
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23. Demo: Hockey Schedule with Live Scores
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24. Takeaway
• LinkRest can do parallel fetching and aggregation from multiple data
sources.
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25. Great Minds Think Alike
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26. Questions?
http://linkrest.io/
@andrus_a
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