Chapter 24. Neo4jTemplate

The Neo4jTemplate offers the convenient API of Spring templates for the Neo4j graph database. It is initialized with a GraphDatabaseService which is thread-safe to use.

24.1. Basic operations

For direct retrieval of nodes and relationships the getReferenceNode, getNode and getRelationship can be used.

There are methods (createNode and createRelationship) for creating nodes and relationships that automatically set provided properties and optionally index certain fields.

Neo4jOperations neo = new Neo4jTemplate(grapDatabase);

Node michael = neo.createNode(_("name","Michael"));
Node mark = neo.createNode(_("name","Mark"));
Node thomas = neo.createNode(_("name","Thomas"));

neo.createRelationship(mark,thomas, WORKS_WITH, _("project","spring-data"));

neo.index("devs",thomas, "name","Thomas");

assert "Mark".equals(neo.query("devs","name","Mark",new NodeNamePathMapper()));

24.2. Indexing

Adding nodes and relationships to an index is achieved using the index method.

Query methods either take a field / value combination to look for exact matches in the index or a lucene query object or string to handle more complex queries. All query methods provide Path results to a PathMapper.

24.3. Traversal

Traversal methods are at the core of graph operations. As such, they are fully supported in the Neo4jTemplate. The traverseNext method traverses to the direct neighbours of the start node filtering the relationships according to its parameters.

The traverse method covers the full traversal operation that takes a powerful TraversalDescription (most probably built from the Traversal.description() DSL) and runs it from the start node. Each path that is returned via the traversal is passed to the PathMapper to be processed accordingly.

24.4. Path abstraction and PathMapper

For the querying operations Neo4jTemplate unifies the result with the Path abstraction that comes from Neo4j. Much like a resultset a path contains nodes() and relationships() starting at a startNode() and ending with aendNode(), the lastRelationship() is also available separately. The Path abstraction also wraps results that contain just nodes or relationships.

Using implementations of PathMapper<T> and PathMapper.WithoutResult (comparable with RowMapper and RowCallbackHandler) the paths can be converted to arbitrary Java objects.

With EntityPath and EntityMapper there is also support for using annotation based NodeEntities within the Path and PathMapper constructs.

24.5. Transaction handling/management

The Neo4jTemplate provides configurable implicit transactions for all its methods. By default it creates a transaction for each call (which is a no-op if there is already a transaction running). If you call the constructor with the useExplicitTransactions parameter set to true, it won't create any transactions so you have to provide them using @Transactional or the TransactionTemplate.