How to fetch pattern variable with node and relationships (if present)

Question

Suppose, we have the following data in neo4j DB ->

The java entity representation is as follows ->

 @NodeEntity
public class Place {
    @Id
    @GeneratedValue
    private Long id;

    private String name;
}

@NodeEntity
public class Monument {
    @Id
    @GeneratedValue
    private Long id;

    private String name;
}

@NodeEntity
public class Person {
    @Id
    @GeneratedValue
    private Long id;

    private String name;

    @Relationship(type = "VISITED", direction = Relationship.OUTGOING)
    private Monument monument;

    @Relationship(type = "STAYS", direction = Relationship.OUTGOING)
    private Place place;
}

Now, I want to fetch all persons also populating the linked place and monument, if present. This means, the cypher query will not only provide me List< Person> as result and the Monument and Place object should also be linked with each Person object, if the links are available (and otherwise null). To clarify it further, for Person 'Ron', I should be able to see the monument he visited and the place he stays, without performing any more queries to fetch the relationships. Similarly, for Person 'April', I should be able to see where she stays, but will not know which monument she visited because there is no link there.

With my basic knowledge in Cypher Query language, I have tried but could not get the desired result.

If I provide both the relations in the query and fetch the corresponding pattern variable, I only get the Person 'Ron' in the result.

MATCH p=(place:Place)<-[STAYS]-(person:Person)-[VISITED]->(monument:Monument) RETURN p

If I only provide the relation 'STAYS', I get 'Ron' and 'April'.

MATCH p=(person:Person)-[STAYS]->(place:Place) RETURN p

If I query without the relationships, I only get the Person object and the monument and place are not linked [getMonument() and getPlace() is null even for Person 'Ron'].

MATCH p=(person:Person) RETURN p

I could not find a query where I get all of these.

Christoph P Christoph P · Accepted Answer · 2018-08-23T16:10:17

You need to put the relations into optional matches, like this:

MATCH (person:Person) 
OPTIONAL MATCH (person)-[:VISITED]->(monument) 
OPTIONAL MATCH (person)-[:STAYS]->(place)
return person, place, monument

Otherwise, neo4j treats the relations in your query 1) as required, that's why 'Ron' will be the only result.

How to fetch pattern variable with node and relationships (if present)

1 Answers