Filtering on pattern using NOT deprecated

Question

When I write a cypher query with Filter on patterns using NOT, the Neo4j browser shows the following warning:

This feature is deprecated and will be removed in future versions.

Coercion of list to boolean is deprecated. Please consider using `NOT isEmpty(...)` instead.

My query is:

MATCH (a)-->(b)
WHERE NOT (b)-->(a)
RETURN a, b

Is there a better way to write this query, so it works in future Neo4j version?

Answer 1

You could be using NOT exists().

For a given

CREATE (b:User{name:'B'})-[:ANY]->(:User{name:'A'})-[:ANY]->(b)<-[:ANY]-(:User{name:'C'})

Your query returns:

???????????????????????????
?"a"         ?"b"         ?
???????????????????????????
?{"name":"C"}?{"name":"B"}?
???????????????????????????

If you use

MATCH (a)-->(b)
WHERE NOT exists((b)-->(a))
RETURN a, b

It also returns

???????????????????????????
?"a"         ?"b"         ?
???????????????????????????
?{"name":"C"}?{"name":"B"}?
???????????????????????????

but uses the exists(Pattern) clause that is not deprecated.

Answer 2

Both isEmpty() and exists() function/predicate will work.

MATCH (a)-->(b)
WHERE NOT IsEmpty((b)-->(a))
RETURN a, b

OR

MATCH (a)-->(b)
WHERE NOT exists((b)-->(a))
RETURN a, b