Cypher: Neo4j query language - Neo4j in Action - page 148

The smart bit comes in the where clause . You use the NODES(p) Cypher function
to extract the collection of all nodes in the given path. You check that each node has the
facebookId property by using the HAS function. Then you use the ALL function to ap-
ply the HAS predicate to every element of the collection of nodes. The function ALL will
return true if every element in the given iterable matches the predicate, so if one of the
nodes on the path p doesn't have a facebookId property, the path will be discarded.
Finally, you return the paths that fulfill all criteria . The path will contain all people
John will need to contact so he can be introduced to Kate on Facebook.
You've seen quite a few functions in action in this example:
• HAS(graphEntity.propertyName) —Returns true if the property with a given
name exists on a node or relationship.
• NODES(path) —Transforms a path into an iterable collection of nodes.
• ALL(x in collection where predicate(x)) —Returns true if every single element
of collection matches the given predicate .
Neo4j supports a lot more functions with similar purposes to the ones we described here.
For example, like the NODES(path) function, the RELATIONSHIPS(path) function
returns a collection of all relationships on the given path.
In addition to ALL , Neo4j supports other predicate-based Boolean functions:
• NONE(x in collection where predicate(x)) —Returns true if no elements of the
supplied collection match the predicate; otherwise it returns false .
• ANY(x in collection where predicate(x)) —Returns true if at least one element
matches the predicate; if none matches, it returns false .
• SINGLE(x in collection where predicate(x)) —Returns true if exactly one ele-
ment of the collection matches the predicate; if no elements or more than one ele-
ment matches, this function returns false .