Grails and Neo4j

Stefan Armbruster

gr8conf CPH, 2011 May 19th

About myself

●located in Munich/Germany●freelancer since 10 years ●cofounder of Netjay●Java +10 years, Groovy ~5 years, Grails 3+ years●author of some Grails plugins●cofounder of the usergroup in Munich●passionate volunteer firefighter●twitter: darthvader42●http://blog.armbruster-it.de

What's wrong with SQL?

What's about the hype of NoSQL?

4 trends

●much larger data sets: ● IDC comparison: 2010 to 2007 is 40 : 1

●data gets more connected●semi-structured data●horizontal scalability – distributed architecture

One size fits all?

exploring the nosql-landscape

Key-Value:Key-Value:➢RIAK *➢Redis *➢Membase

Bigtable:Bigtable:➢Hadoop / Hbase *➢SimpleDB➢Cassandra **

Graph:Graph:➢InfiniteGraph➢Neo4j *

DocumentDocument:➢CouchDB * ➢Mongo *

*: GORM compliant implementation, **: Grails support without GORM

nosql is not the silver bullet

neo4j basic building blocks

1) nodes

2) relationships

3) properties on both, nodes and relationship

that's it!

neo4j

querying neo4j

●simple way: navigate the relationships●more powerful: use a traverser with callbacks for

● decide where to end● decide if node should be part of the result

SQL querying vs traversing

Node node = // retrieve the starting poing

def myFriendsAndFriends = node.traverse( BREADTH_FIRST, { it.depth()<3 } as StopEvaluator, { true } as RetrunableEvaluator, DynamicRelationshipType.withName('friend'), Direction.OUTGOING).allNodes

SQL challenge: SQL statement that retrieves friends up to n'th grade. Anyone?

Neo4j: using a traverser:

query performance

some benchmark data:

– each Person has 50 friends in avg

Database # persons query time

Relational 1.000 2000 ms

Neo4j 1.000 2 ms

Neo4j 1.000.000 2 ms

accessing the database

Choosing an implementation of GraphDatabase:

● EmbeddedGraphDatabase: just local to JVM

● RestGraphDatabase (https://github.com/jexp/neo4j-java-rest-binding)

● HighAvailableGraphDatabase: uses Zookeeper

neo4j - Licensing

3 editions:

community: GPL or $

advanced: AGPL or $

enterprise: AGPL or $

history of nosql & neo4j for Grails

end 2009: first version of neo4j plugin

during 2010: GORM for nosql– 'inconsequential' -> 'spring-data-mapping'

end 2010: 'spring-data-graph'– aspectj based injection of JPA like methods

– focussed at Roo an POWAs

– "not the right approach for Grails" (IMHO)

May 2011: Neo4j for Grails using spring-data-mapping

GORM: spring-data-mapping

●provides abstraction layer●TCK ●various implementations:

● hibernate, jpa● gemfire, redis, riak ● mongo, jcr● neo4j <- the new child on the block

dependencies

interfaces/abstract base classes in GORM

●Datastore:● create sessions● manage connection to low-level storage

●MappingContext:● holds metainformation about mapping domain classes to the underlying

datastore (type conversion, list of EntityPersisters,...)

●EntityPersister:● does the dirty work: interact with low level datastore

●Session:● similar HibernateSession

●Query:● knows how to query the datastore by criteria (criterion, projections,...)

mapping domain model to nodespace

domain class

association

domain classinstance

domain instanceproperty

reference node

subreference

subreference node

instance

properties

praying to the demo god....

currently working in neo4j plugin

●passing >90% of GORM TCK (hurray!)●accessing embedded, REST and [HA datasources]●property type conversion●access to native API●<DomainClass>.traverseStatic, <instance>.traverse

currently not working in neo4j plugin

●nasty bug: some trouble if a domain class references itself -> StackOverflowException

●Transactions●Optimistic Locking●Query performance not as good as could be●Indexing

roadmap

●Write docs & publish●Handle relationship to self (Neo4j 1.4?)●Support for arbitrary attributes●Support for indexing (and its usage in criteria queries)●Embed some controller/servlet to visually navigate

the nodespace (SVG?)●Support for migrations?●... your suggestions?

Q & A

References

general overview of nosql:

– http://www.nosql-databases.org/

http://www.neo4j.org

neo4j grails plugin:

– source: https://github.com/sarmbruster/spring-data-mapping

– issues: http://jira.grails.org/browse/GPNEO4J

https://github.com/jexp/neo4j-java-rest-binding

site running grails w/ neo4j: http://www.fanorakel.de

my blog: http://blog.armbruster-it.de,

twitter: darthvader42