The Neo4j Traversal Framework Java API is a callback-based, lazily-executed way of specifying desired movements through a graph in Java. Some traversal examples can be found in Traversing a graph.
A traversal takes a start node on a graph and returns a set of paths representing the visited nodes and their relationships. Traversals are defined by a traversal description, which may contain the following elements:
Starting node — defines where the traversal begins.
Pathexpander — defines what to traverse, typically in terms of relationship direction and type.
Uniqueness — defines the restrictions of previously traversed nodes and relationships on the graph.
Evaluator — decides what to return and whether to stop or continue the traversal beyond its current position.
Order — defines in which order paths are expanded, for example,
Using the Traversal Framework
The Traversal Framework can be used embedded in Java applications. It can also be used when extending Neo4j with a User-defined Procedure. For an example, see User-defined procedure with a Traversal Framework.
Traversal Framework vs Cypher
Although the Traversal Framework is less readable and more complex than the Cypher query language, it offers a powerful approach to traversing the graph. This is because the Traversal Framework can dynamically make custom choices at each step of the traversal, thus making the process more expressive and potentially more performant than Cypher.
Some of the advantages of using the Traversal Framework over Cypher include:
The Traversal Framework allows the use of any desired Java library to help in the evaluation of the traversal.
It allows customized pruning during the traversal of a path, which could potentially improve the performance of a traversal. See Evaluator for more information.
With Cypher, it is not possible to specify the order in which paths are expanded (e.g. depth-first). However, with the Traversal Framework, it is possible to specify the order of paths traversed.
With Cypher, relationships are only traversed when
RELATIONSHIP_GLOBALuniqueness is specified. By using the Traversal Framework, it is possible to specify the uniqueness constraints on the path traversed.
It is generally recommended to use Cypher wherever it is possible. However, when using the Traversal Framework, keep in mind that:
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