Spring Data Neo4j - Developer Notes

Neo4j - [IS_A] -> Property Graph

Nodes with key-value properties are connected by typed, directed relationships with properties.

TODO put in a pretty picture

Cypher is a query language:

start movie=(id) match movie<-[:ACTS_IN]-actor
where actor.age > 20 return movie, actor.name
order by movie.title

Traversals walk the graph in the prescribed way

TraversalDescription actors = Traversal.description()
  .relationships("ACTS_IN").filter(returnAllButStartNode());

for (Node actor : actors.traverse(movie))
 ...

Transactional: TX needed for write operations

try (Transaction tx=graphDatabaseService.beginTx()) {
  ... graph operations ...
  tx.success();
} catch(Exception e) {
  tx.failure();
}

Maven Dependency

   <dependency>
       <groupId>org.springframework.data</groupId>
       <artifactId>spring-data-neo4j[-aspects]</artifactId>
       <version>2.0.0.RC1</version>
   </dependency>

Spring-Config

<beans ...
 xmlns:neo4j="http://www.swf.org/schema/data/neo4j"
   xsi:schemaLocation=
   "http://www.sfw.org/schema/data/neo4j" ...>

...
<neo4j:config store-dir="graph.db"/>
<neo4j:repositories base-package="com.example.repositories"/>
...
</beans>

Testing

<neo4j:config graphDatabaseService="gds"/>
<bean id="gds" class="...ImpermanentGraphDatabase"/>

REST

<neo4j:config graphDatabaseService="rds"/>
<bean id="rds" class="...SpringRestGraphDatabase"/>

Entity - Annotations

@NodeEntity marks a domain class as backed by a node in the graph
@RelationshipEntity marks a domain class as backed by a relationship in the graph
@GraphId Field for id
@Indexed([fulltext=true],[indexName=name]) Auto-Indexing
@RelatedTo([direction=Direction], [type=TYPE]) define type and direction of relationship on Entity, Iterable<E>, Set<E> fields
@RelatedToVia([direction=Direction], [type=TYPE]) like @RelatedTo, but targets Relationship-Entities
@Query(query, [type=QueryType]) computed field, executes graph query in Cypher
@GraphTraversal(traversal=~TraversalBuilder.class, [elementClass=Person.class]) computed field, executes traversal starting from entity-node

Example

@NodeEntity
public class Movie {

   @GraphId Long id;

   @Indexed(fulltext = true, indexName = "search")
   String title;

   Person director;

   @RelatedTo(type="ACTS_IN", direction = INCOMING)
   Set<Person> actors;

   @RelatedToVia(type = "RATED")
   Iterable<Rating> ratings;
   
   @Query("start movie=node({self}) match
           movie-->genre<--similar return similar")
   Iterable<Movie> similarMovies;
}

Repositories

interface MovieRepository extends GraphRepository<Movie> {
 @Query("start movie={0} match m<-[rating:RATED]-user
       return rating")
 Iterable<Rating> getRatings(Movie movie);
 // Co-Actors
 Iterable<Person> findByActorsMoviesActorName(name)
}

<neo4j:repositories base-package="com.example.dao"/>

Provide CRUD, Finder, Query and Traversal abilities by default.
Automatic Finders can be derived from method names (like (G)Rails) or @Query annotations.
custom method implementations possible

Neo4jTemplate

convenience methods for graph operations, transaction and exception handling
index lookups, cypher queries, traversal execution with fluent result converter API
preconfigured and customizable conversion of results to a variety of types

AspectJ - ActiveRecordMixin

adds the following methods, when implementing the NodeBacked interface

getPersistentState()
relateTo(target, ...),
getRelationshipTo(...)
persist(),
remove(),
detach()
...

Roo Add-on

roo> addon search graph
roo> addon install id --searchResultId 01
roo> project --topLevelPackage net.cineasts
roo> graph setup --provider NEO4J --databaseLocation cineasts
roo> graph entity --class ~.model.Movie
roo> field string title
roo> graph entity --class ~.model.Actor
roo> field string name
roo> graph relationship --to Movie --from Actor
  --fieldName movies --type ACTS_IN --cardinality ONE_TO_MANY
roo> controller all --package ~.web

Libraries

spring-data-neo4j

Provides Repository based Object <-> Graph Mapping that copies data from and to the graph database.

spring-data-neo4j-aspects

Provides transparent property and relationship mapping inside of transactions with live read- and write-through to the graph database.

spring-data-neo4j-cross-store

Allows to partially store properties and relationships of JPA entities in the graph database.

spring-data-neo4j-rest

Provides transparent remote access to Neo4j-Server via its REST Api (uses org.neo4j:neo4j-rest-graphdb)

AspectJ - STS / eclipse setup

STS 2.7.1
import existing maven project or set aspectj nature
Project Properties -> AspectJ -> Aspect Paths
AspectJ Configurator installed
sometimes build after restart required

Developer Notes