jugmarche: neo4j 2 (cypher)

Neo4j 2: Learning CypherJUG Marche - June 2014

Onofrio Panzarino

Graph databases and me

● RDF (Semantic web)○ 2004-2005: Sesame (SPARQL)

● Neo4j○ 2011: Java API (Embedded), Traversers○ 2013: Cypher

Twitter: @onof80 Blog: http://learningcypher.blogspot.com My book: Learning Cypher

What is Neo4j

- Graph database- ACID transaction- 2 running modes > Embedded (JAVA API) > Server (REST)- Cypher Query Language

Model: nodes and relationships

Source: http://gist.neo4j.org/?8635758

Schema?

Schemaless (key-value)

Nodes: > propertiesRelationships: > properties

SchemaNodes:

0+ LabelsRelationships: 1 TypeIndexes+Constraints

Querying: REST API

Properties of node with id 32:GET http://localhost:7474/db/data/node/32/properties

{

"user": "@onof80",

"lastLogin": 1394304000,

"tags": ["Java","Scala","NoSql"]

}

Traversing the graphfor ( Path position : db.traversalDescription()

.depthFirst()

.relationships( Rels.KNOWS, Direction.INCOMING )

.evaluator( Evaluators.toDepth( 5 ) )

.traverse( node6 ) )

{

output += position + "\n";

}

(6)

(6)<--[KNOWS,1]--(3)

(6)<--[KNOWS,1]--(3)<--[KNOWS,6]--(0)

(6)<--[KNOWS,1]--(3)<--[KNOWS,6]--(0)<--[KNOWS,4]--(5)

Powerful but hardcoded

Querying with Cypher

START n=node(10)MATCH path =(n)<-[:KNOWS*0..5]-()RETURN path

http://console.neo4j.org/

Create a full path

CREATE (a:Language { name: "Java"}),

(b:Language { name: "Scala" }),

(c:Language { name: "JavaScript" }),

(jvm:Platfom { name: "JVM" }),

path=(a)-[r:RUNS_ON]->(jvm)

<-[r2:RUNS_ON]-(b)

RETURN path

MERGE

Look for a pattern:● Found? Match it● Else create it

MERGE (a:Language { name: "Java" })

SET a.version = 8

RETURN a

Idempotent operations

MATCH (a:Language)REMOVE a.version

MATCH (a:Language)DELETE a

But...

MERGE (a:Language { name: "Java" })

ON MATCH SET a.version = a.version + 1

ON CREATE SET a.version = 1

RETURN a

Optional paths

MATCH (a:Language)OPTIONAL MATCH (a)-[:RUNS_ON]-(b)RETURN a,bORDER BY a.name

Aggregations

MATCH (a:Language)OPTIONALMATCH (a)-[:RUNS_ON]-(b)RETURN b.name, COUNT(*)

Other keywords

Splitting queriesWITH

Manipulating collectionsEXTRACT, FILTER, REDUCE

PredicatesALL, ANY, SINGLE, NONE

More features

IntegrationLOAD CSV WITH HEADERS

FROM <file> AS line

CREATE ...

ProfilingPROFILE <query>

Too simple domain?

http://gist.neo4j.org/

Any questions?

Q&A

More infos:http://docs.neo4j.org/ My bookAll Neo4j books