Building Community APIs usingGraphQL, Neo4j, and Kotlin

Michael Hunger

Kotlin MeetupJan 2018

(Michael Hunger)-[:WORKS_FOR]->(Neo4j)

michael@neo4j.com | @mesirii | github.com/jexp | jexp.de/blog

Michael Hunger - Developer Relations Engineering @Neo4j

My History With

Graphs &

Neo4j

Community Graph

KotlinAppDev

GraphQL

ExtendingNeo4j

Why Graphs?

Because the World is a Graph!

Unraveling the Cancer Code with

Graphs

Real-Time Recommendation

s

Fraud Detection

Network &IT

Operations

Master Data Management

Graph-Based Search

Identity & Access Management

Using Neo4j Graphs

Machine Learning is Based on Graphs

Neo4j

Open Source Database for HighlyConnected Data

The Whiteboard Model Is the Physical Model

Eliminates Graph-to-Relational Mapping

In your data modelBridge the gap

between business and IT models

In your applicationGreatly reduce need for application code

CAR

name: “Dan”born: May 29, 1970

twitter: “@dan”name: “Ann”

born: Dec 5, 1975

since: Jan 10, 2011

brand: “Volvo”model: “V70”

Property Graph Model Components

Nodes

• The objects in the graph

• Can have name-value properties

• Can be labeled

Relationships

• Relate nodes by type and direction

• Can have name-value properties

LOVES

LOVES

LIVES WITHPERSON PERSON

Relational Versus Graph Models

Relational Model Graph Model

KNOWSANDREAS

TOBIAS

MICA

DELIA

Person FriendPerson-Friend

ANDREASDELIA

TOBIAS

MICA

Cypher: Powerful and Expressive Query Language

MATCH (:Person { name:“Dan”} ) -[:LOVES]-> (:Person { name:“Ann”} )

LOVES

Dan Ann

LABEL PROPERTY

NODE NODE

LABEL PROPERTY

Official Language Drivers• Foundational drivers for

most programming languages

• Bolt: streaming binary wire protocol

• Authoritative mapping to native type system, uniform across drivers

• Pluggable into richer frameworks

JavaScript Java .NET PythonCommunity

Drivers

Drivers

Bolt

Kotlin Wrapper• Wraps Neo4j Java Driver

• Idiomatic API

• Use Data Classes as– Parameters

– Results

– Destruct data class to Map

• Serializer (DateTime, Enum)

Bolt

https://github.com/erictsangx/kotlin-neo4j

Kotlin Wrapper – Connect & Insert

https://github.com/erictsangx/kotlin-neo4j

Kotlin Wrapper – Query & Map

https://github.com/erictsangx/kotlin-neo4j

Object Graph Mapping

Spring Data Neo4jNeo4j - OGM

Object Graph Mapping

• Neo4j OGM

• Spring Data Neo4j

– Dedicated support for Kotlin classes in Spring / Spring Data

– Persistence Constructors (PR 405)

– Example Project:

– github.com/neo4j-examples/movies-kotlin-spring-data-neo4j

Movie.kt

MovieRepository.kt

Community Graph

Making Sense of Developer Activity

github.com/community-graph

Developer Channels

User

Event

MessageTweet

LocationProject

TopicTag

QuestionAnswer

TopicTag

There is much more to it

Approach

• Use Jupyter Notebooks– Read Data from APIs

– Import into Neo4j Graph

• Evolve into AWS script– spin instance up for any community

– based on search tags

• Query for analytics, newsletter, active people

Community Graphs

• Neo4j

• GraphQL

• Kotlin

• Angular

• ... more planned ...

Demo

Kotlin Community Graph

Community RadarKotlin Conf 2017

Twitter Appreciation Wall App

github.com/community-graph/community-radar

Community Radar

• Kotlin Backend

– finds people that have been mentioned a lot ortagged with a hashtag

– and recent tweets

• Angular Front-End

• Statistics Service with React UI (WIP)

Stats Repository

Neo4j-GraphQL

Neo4j Extension in Kotlin

neo4j.com/developer/graphql & grandstack.io

GraphQL

• GraphQL is an API query language

• Based on a typesafe schema

• Contract between front & backend

• Flexible queries, nested „shape of data“

• Updates via Mutations

GraphQLquery {

Movie(title:"The Matrix") {titlereleasedtaglineactors {

nameborn

}}

}

type Movie {title: String!released: Inttagline: Stringactors: [Person]

}

type Person {name: String!born: Intmovies: [Movie]

}

Neo4j-GraphQL

• Add support to Neo4j via extension

• Translate GraphQL query to Cypher based on schema

• Execute & transform results

• Integrate graphql-java

• Add custom directives & generated mutations

Code!

Lessons Learned• Started in Java switched to Kotlin = < 3• Convince other devs• Interoperability is impressive• Language & Query transformations work well• Extension functions are great for glue code• Updates were painless• I like: ?: / ?. / let / use

Lessons Learned

• Watch out for Nullability in Java libraries/APIs

• Too deep list comprehensions

• Too many „it“

• „?“ operator would be great

• Local return from closures

• Watch out for fun foo(): Any = {...}

Extending Neo4j

User Defined Procedures

Any JVM Language will do

• Nullable Inputs / Outputs

• Some Annotations needed (@JvmField)

• Example Project– github.com/mfalcier/neo4j-kotlin-procedure-example

Example

Other Projects

Looking for morepointers

Other Projects

• Open Data (Healthcare) Import, Queries, Object-Mapping– slideshare.net/neo4j/open-data-with-neo4j-and-kotlin

• Neo4j Cloudfoundry Service Broker

• Extension Functions for Neo4j‘s Java API

– github.com/pisolutions/neo4j-kotlin

Thank you!Questions ?

neo4j.com/slack@neo4j