This document summarizes a presentation about Neo4j and Cypher. It introduces Neo4j as a graph database that supports ACID transactions and can be run embedded or on a server. It describes how Neo4j models data as nodes and relationships and supports optional schemas. It provides examples of querying Neo4j with both the REST API and the Cypher query language, demonstrating commands like MATCH, MERGE, OPTIONAL MATCH, and aggregations. It also discusses more advanced Cypher features and taking questions.

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