Document Oriented Access to Graphs

Document oriented access
to a graph database
Using a Neo4j Server Extension
Michael Hunger - @mesirii
http://github.com/jexp/cypher-rs

Graphs are great
• for modeling highly connected domains
• ﬁnding patterns to answer questions
• high performance traversals

Graphs suck
• for compact access patterns
• use-case speciﬁc views
• easy integration in modern webapps

Documents are great
• for everything that eats JSON
• especially modern JavaScript based webapps
• as dedicated projections of a domain
• compact representation

Documents are great
{
name:"Michael",
age:39,
children:[„Selina“,“Rana“,"Selma"],
address: { street: „Holbeinstr“, city: „Dresden“}
hobbies: [„Coding“,„Buchbar“,“MUD MorgenGrauen“]
blog: „http://jexp.de/blog“
}

Documents suck
• for different projections besides the main use-case
• for connected data
• for cross-document linking
• for less redundancy / duplication

Documents suck
{
name:"Michael",
age:39,
children:[„Selina“,“Rana“,"Selma"],
address: { street: „Holbeinstr“, city: „Dresden“}
hobbies: [„Coding“,„Buchbar“,“MUD MorgenGrauen“]
blog: „http://jexp.de/blog“
}
„Show people by hobby“

Documents suck
{ _id: 1,
name:“Michael“,
works_at: dbref:2
}
{ _id: 2,
name:“Neo Technology“,
employees: [dbref:1]
}
„Link Employees to Companies“

What can we do?
• Use a document oriented access layer for a graph database
• Use graph queries whose results project into documents
• Make them easily accessible

How can we do that?
• Use Cypher in Neo4j 2.0
• Support for literal maps
• Parameters, including maps

Cypher & Maps - Results
MATCH (n:User)
WHERE n.name={name}
RETURN n
// returns a map of the node’s properties
RETURN {id: id(n), labels: labels(n), data : n}

Cypher & Maps - Results (II)
MATCH (n:User)-[:PARENT_OF]->(child)
WHERE n.name={name}
RETURN {name:n.name, children:collect(child.name)}

Cypher & Maps - Params
CREATE (u:User { name: {p}.name, age: {p}.age})
RETURN u
CREATE (u:User {params})
RETURN u

How can we do that?
• Create a RESTful API to
• Provide endpoints that represent on Cypher queries
• Use GET, POST with parameters to execute those endpoints
• Return only JSON documents or lists of those

How do we implement it?
• Add a Neo4j-Server-Extension
• Jersey JAX-RS
• Save queries in graph properties
• Execute queries for reads on GET
• Execute queries for reads and writes on POST
• Support JSON and CSV as payload
• Batch transactional write operations

What does it look like?
• Examples for
• Managing endpoints
• Querying Endpoints
• Writing to Endpoints

Create Endpoint
PUT /cypher-rs/users
Body: match (n:User) where n.name={name} return n
--> 201 Location: /cypher-rs/users
PUT /cypher-rs/create-user
Body: create (n:Node {name:{name},age:{age}})
--> 201 Location: /cypher-rs/create-user

GET Request
GET /cypher-rs/users?name=Andres
--> 200
{"name":"Andres",
"age":21,"children":["Cypher","L.","N."]}
GET /cypher-rs/users?name=NotExists
--> 204

POST Request - Read
POST /cypher-rs/users
Content-type: application/json
Body: {"name":"Andres"}
--> 200
{"name":"Andres","age":21,
"children":["Cypher","L.","N."]}

POST Request - Read (II)
POST /cypher-rs/users
Body: [{"name":"Andres"},{"name":"Peter"},{"name":"NotExists"}]
!
--> 200
[{"name":"Andres","age":21,"children":["Cypher","L.","N."]},
{"name":"Peter" ,“age“:32,"children":["Neo4j","O.","K."]},
null]

POST Request - Write JSON
POST /cypher-rs/create-user
Body: {"name":"Andres","age":21}
--> 201

POST Request - Write JSON (II)
POST /cypher-rs/create-user
Body: [{"name":"Andres","age":21},
{"name":"Peter", "age":40},
--> 201

POST Request - Write CSV (III)
POST /cypher-rs/create-user[?batch=20000&delim=,]
Content-type: text/plain
Body: name,agenAndres,21nPeter,40
--> 201

Delete Endpoint
DELETE /cypher-rs/users
--> 200

List Endpoints
GET /cypher-rs
--> 200
[„create-users“, „users“]

Inspect Endpoint
GET /cypher-rs/users/query
--> 200
match (n:User) where n.name={name} return n

Possible Results
single column, single row!
{"name":"Andres","age":21,"children":["Cypher","L.","N."]}
single column, multiple rows!
[
{"name":"Andres","age":21,"children":["Cypher","L.","N."]},
{"name":"Peter", "age":40,"children":["Neo4j","O.","K."]}
]

Possible Results (II)
multiple columns, single row!
{"user": "Andres", "friends": ["Peter","Michael"]}
multiple columns, multiple rows!
[
{"user": "Andres", "friends": ["Peter","Michael"]},
{"user": "Michael","friends": ["Peter","Andres"]},
{"user": "Peter", "friends": ["Andres","Michael"]}
]

Usage
Build with mvn clean install dependency:copy-dependencies
Copy ﬁles
cypher-rs-2.0-SNAPSHOT.jar opencsv-2.3.jar to path/to/server/plugins
Add this line to path/to/server/conf/neo4j-server.properties
org.neo4j.server.thirdparty_jaxrs_classes=org.neo4j.cypher_rs=/cypher-rs
Restart

Next Steps
• Add streaming
• Rule the world

Document Oriented Access to Graphs

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