Neo4j Cypher query with null or not null value - neo4j

Question

In my Spring Data Neo4j project I have a following entities:
#NodeEntity
public class Decision extends Commentable {
private final static String CONTAINS = "CONTAINS";
private final static String DEFINED_BY = "DEFINED_BY";
private String name;
#Relationship(type = DEFINED_BY, direction = Relationship.INCOMING)
private Set<CriterionGroup> criterionGroups = new HashSet<>();
#Relationship(type = DEFINED_BY, direction = Relationship.INCOMING)
private Set<Criterion> criteria = new HashSet<>();
...
}
#NodeEntity
public class Criterion extends Authorable {
private final static String CONTAINS = "CONTAINS";
private final static String DEFINED_BY = "DEFINED_BY";
private String name;
#Relationship(type = CONTAINS, direction = Relationship.INCOMING)
private CriterionGroup group;
#Relationship(type = DEFINED_BY, direction = Relationship.OUTGOING)
private Decision owner;
...
}
#NodeEntity
public class CriterionGroup extends Authorable {
private final static String DEFINED_BY = "DEFINED_BY";
private final static String CONTAINS = "CONTAINS";
private String name;
#Relationship(type = DEFINED_BY, direction = Relationship.OUTGOING)
private Decision owner;
#Relationship(type = CONTAINS, direction = Relationship.OUTGOING)
private Set<Criterion> criteria = new HashSet<>();
...
}
I have a following SDN repository method:
#Query("MATCH (d:Decision)<-[:DEFINED_BY]-(c:Criterion) WHERE id(d) = {decisionId} and c.name = {name} RETURN c")
Criterion findCriterionDefinedByDecisionByName(#Param("decisionId") Long decisionId, #Param("name") String name);
Based on this query I can get Criterion that belongs to Decision and have a specific name.
Criterion in my domain model may (or may not)belong to CriterionGroup.
I need to extend this query in order to add one more condition for checking CriterionGroup associated with this Criterion. In another words I need to return Criterion with a specific {name} for a specific {decisionId} that belongs(or not in case of null value) to a provided {criterionGroupId}. In case of {criterionGroupId} == null I need to find Criterion that do not belong to any CriterionGroup.
I need something like this:
#Query("MATCH (d:Decision)<-[:DEFINED_BY]-(c:Criterion)...????????...... WHERE id(d) = {decisionId} and c.name = {name} RETURN c")
Criterion findCriterionDefinedByDecisionByName(#Param("decisionId") Long decisionId, #Param("name") String name, #Param("criterionGroupId") Long criterionGroupId);
Please help me to write this query.

Answer 1

This should work, and shouldn't be too slow either unless you have tens of thousands of CriterionGroups per Criterion:
MATCH (d:Decision)<-[:DEFINED_BY]-(c:Criterion)
WHERE id(d) = {decisionId}
AND c.name = {name}
OPTIONAL MATCH (c)<-[:CONTAINS]-(cg:CriterionGroup)
WITH c, extract(g IN collect(cg) | id(g)) AS cgIds
WHERE CASE
WHEN {criterionGroupId} IS NULL THEN size(cgIds) = 0
ELSE {criterionGroupId} IN cgIds
END
RETURN c
Alternatively, you could have 2 methods in your Repository, to manage each case directly, using
MATCH (d:Decision)<-[:DEFINED_BY]-(c:Criterion)
WHERE id(d) = {decisionId}
AND c.name = {name}
AND NOT (c)<-[:CONTAINS]-(:CriterionGroup)
RETURN c
when criterionGroupId is null, and
MATCH (d:Decision)<-[:DEFINED_BY]-(c:Criterion),
(c)<-[:CONTAINS]-(cg:CriterionGroup)
WHERE id(d) = {decisionId}
AND c.name = {name}
AND id(cg) = {criterionGroupId}
RETURN c
otherwise.