StackOverflowException with custom query and result contains circular references

[gonzalad]

Hello,

I'm getting a StackOverflowException when executing a custom query and whent the result contains circular references.
I'm having this issue with SDN 6.2.3 (and 6.1.10).
I didn't have this issue in 6.1.5.

Since SDN works record-oriented I would expected to have some lines with duplicated entity instances (different instances, but same data), but I wouldn't have expected the stackOverflowException.

My entites:

@Node(labels = "Type")
public class Type {

    @Id
    @GeneratedValue
    private Long id;
    private String code;
    @Relationship(type = "IS_ALLOWED")
    private List<Type> allowed = new ArrayList<>();

   // getters/setters ommited
}

My repository:

@Repository
public interface TypeRepository extends Neo4jRepository<Type, Long> {

    @Query("MATCH (nt:Type)\n"
            + "OPTIONAL MATCH (nt)-[raut:IS_ALLOWED]->(aut)\n"
            + "RETURN nt,\n"
            + "  collect(raut), collect(aut)\n"
    )
    List<Type> findAllTypes();
}

And my unit test reproducing the error:

    @Test
    void findWithCircularReferenceThrowsStackOverflowException() {
        Type formation = new Type().code("FORMATION");
        Type groupement = new Type().code("GROUPEMENT");
        formation.allowed(groupement);
        groupement.allowed(groupement);
        List<Type> toSave = List.of(
                formation,
                groupement
        );
        repository.saveAll(toSave);

        List<Type> types = repository.findAllTypes();

        assertThat(types).isNotEmpty();
    }

The unit test is also available here: https://github.com/gonzalad/sdn-circular-references-stackoverflow/blob/master/src/test/java/com/example/sdncircularreferencesstackoverflow/SdnTest.java

Thanks for your help !

[meistermeier]

Thanks for reporting this. Interesting bit on this issue is that it depends on the order of entities coming from the database. If you are interested, you can try it out yourself and change the order of the list-to-save that groupement is the first entity. My version of Neo4j will return them ordered by id (no guarantee, but it works reproducible).
I can reproduce it also in the current development branches.
Some background on this regression(?): it goes hand in hand with a bug fix related to entity population that ensured objects will get the possibility to update their properties incl. relationships if they are not final.
Even though SDN works record oriented, there were some corner cases in which an already populated entity needed to get modified again.

[meistermeier]

There are now snapshot versions available.
6.1.11-SNAPSHOT and 6.2.4-SNAPSHOT for the released versions.
6.3.0-SNAPSHOT and 7.0.0-SNAPSHOT pre-release.
I have tested your reproducer with 6.2.4-SNAPSHOT and it passed. Would be good to get your input also on this.

[gonzalad]

This was fast ! Thanks @meistermeier

I checked 6.1.11-SNAPSHOT with my real application, the fix works.
I checked both 6.1.11-SNAPSHOT and 6.2.4-SNAPSHOT on my testcase, it works too.

Thanks very much once more !

[michael-simons]

Thank you for providing us with great reproducers and feedback! This is contribution to OSS, too.