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Cypher

Neo4j's graph query language

Neo4j's Cypher language is purpose built for working with graph data.

uses patterns to describe graph data
familiar SQL-like clauses
declarative, describing what to find, not how to find it

CREATE

Create a node

Let's use Cypher to generate a small social graph.

CREATE (ee:Person { name: "Emil", from: "Sweden", klout: 99 })

CREATE clause to create data
() parenthesis to indicate a node
ee:Person a variable 'ee' and label 'Person' for the new node
{} brackets to add properties to the node

MATCH

Finding nodes

Now find the node representing Emil:

MATCH (ee:Person) WHERE ee.name = "Emil" RETURN ee;

MATCH clause to specify a pattern of nodes and relationships
(ee:Person) a single node pattern with label 'Person' which will assign matches to the variable 'ee'
WHERE clause to constrain the results
ee.name = "Emil" compares name property to the value "Emil"
RETURN clause used to request particular results

CREATE more

Nodes and relationships

CREATEclauses can create many nodes and relationships at once.

MATCH (ee:Person) WHERE ee.name = "Emil"
CREATE (js:Person { name: "Johan", from: "Sweden", learn: "surfing" }),
(ir:Person { name: "Ian", from: "England", title: "author" }),
(rvb:Person { name: "Rik", from: "Belgium", pet: "Orval" }),
(ally:Person { name: "Allison", from: "California", hobby: "surfing" }),
(ee)-[:KNOWS {since: 2001}]->(js),(ee)-[:KNOWS {rating: 5}]->(ir),
(js)-[:KNOWS]->(ir),(js)-[:KNOWS]->(rvb),
(ir)-[:KNOWS]->(js),(ir)-[:KNOWS]->(ally),
(rvb)-[:KNOWS]->(ally)

Pattern matching

Describe what to find in the graph

For instance, a pattern can be used to find Emil's friends:

MATCH (ee:Person)-[:KNOWS]-(friends)
WHERE ee.name = "Emil" RETURN ee, friends

MATCHclause to describe the pattern from known Nodes to found Nodes
(ee)starts the pattern with a Person (qualified by WHERE)
-[:KNOWS]-matches "KNOWS" relationships (in either direction)
(friends)will be bound to Emil's friends

Recommend

Using patterns

Pattern matching can be used to make recommendations. Johan is learning to surf, so he may want to find a new friend who already does:

MATCH (js:Person)-[:KNOWS]-()-[:KNOWS]-(surfer)
WHERE js.name = "Johan" AND surfer.hobby = "surfing"
RETURN DISTINCT surfer

()empty parenthesis to ignore these nodes
DISTINCTbecause more than one path will match the pattern
surferwill contain Allison, a friend of a friend who surfs

Analyze

Using the visual query plan

Understand how your query works by prepending EXPLAIN or PROFILE:

PROFILE MATCH (js:Person)-[:KNOWS]-()-[:KNOWS]-(surfer)
WHERE js.name = "Johan" AND surfer.hobby = "surfing"
RETURN DISTINCT surfer

Live Cypher warnings

Identify query problems in real time

As you type, the query editor notifies you about deprecated features and potentially expensive queries.

Next steps

Start your application using Cypher to create and query graph data. Use the REST API to monitor the database. In special cases, consider a plugin.

Keep getting started

Intro - a guided tour
Concepts - GraphDB 101
The Movie Graph - create the movie graph
Northwind Graph - from RDBMS to graph