Slides of the JugMarche June meeting, about Neo4j and Cypher

1. Neo4j 2: Learning Cypher
JUG Marche - June 2014
Onofrio Panzarino

2. 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

3. What is Neo4j
- Graph database
- ACID transaction
- 2 running modes
> Embedded (JAVA API)
> Server (REST)
- Cypher Query Language

4. Model: nodes and relationships
Source: http://gist.neo4j.org/?8635758

5. Schema?
Schemaless (key-
value)
Nodes:
> properties
Relationships:
> properties
Schema
Nodes:
0+ Labels
Relationships:
1 Type
Indexes+Constraints

6. 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"]
}

7. Traversing the graph
for ( 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

8. Querying with Cypher
START n=node(10)
MATCH path =(n)<-[:KNOWS*0..5]-()
RETURN path
http://console.neo4j.org/

9. 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

10. MERGE
Look for a pattern:
● Found? Match it
● Else create it
MERGE (a:Language { name: "Java" })
SET a.version = 8
RETURN a

11. Idempotent operations
MATCH (a:Language)
REMOVE a.version
MATCH (a:Language)
DELETE a

12. But...
MERGE (a:Language { name: "Java" })
ON MATCH SET a.version = a.version + 1
ON CREATE SET a.version = 1
RETURN a

13. Optional paths
MATCH (a:Language)
OPTIONAL MATCH (a)-[:RUNS_ON]-(b)
RETURN a,b
ORDER BY a.name

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

15. Other keywords
Splitting queries
WITH
Manipulating collections
EXTRACT, FILTER, REDUCE
Predicates
ALL, ANY, SINGLE, NONE

16. More features
Integration
LOAD CSV WITH HEADERS
FROM <file> AS line
CREATE ...
Profiling
PROFILE <query>

17. Too simple domain?
http://gist.neo4j.org/

18. Any questions?
Q&A
More infos:
http://docs.neo4j.org/
My book
All Neo4j books