Neo4j Cypher Pattern comprehension in return statement

Question

I need to add to my Cypher query's return statement the following Pattern comprehension:

[ (rc:Criterion) WHERE rc.id IN childD.replaceableCriterionIds | {entity: rc} ] AS decisionReplaceableCriteria

but it fails with the following exception:

Caused by: org.neo4j.driver.exceptions.ClientException: Invalid input 'WHERE': expected "-", "<", <ARROW_LEFT_HEAD> or <ARROW_LINE> 

It only works when I'm adding the redundant relationship with another node

[ (rc:Criterion)-[:CREATED_BY]->(:User) WHERE rc.id IN childD.replaceableCriterionIds | {entity: rc} ] AS decisionReplaceableCriteria

The following part is absolutely redundant for my needs:

-[:CREATED_BY]->(:User)

Is it possible to rewrite my pattern comprehension to avoid such redundant syntax?

Answer 1

If you are using Neo4j 5.6+, you can use the COLLECT subquery. Here is a sample snippet:

...
RETURN COLLECT {
    MATCH (rc:Criterion)
    WHERE rc.id IN childD.replaceableCriterionIds
    RETURN {entity: rc}
} AS decisionReplaceableCriteria

In prior versions of Neo4j, you can try a hack:

...
RETURN [ (rc:Criterion)-[*0]->() WHERE rc.id IN childD.replaceableCriterionIds | {entity: rc} ] AS decisionReplaceableCriteria

This uses a variable-length path pattern specifying a length of 0. If you want to see if this variable-length path pattern causes any DB hits, PROFILE your query and look at the VarLengthExpand operation's "db hits".