Bug in connecting objects

[shayantabrizi]

It seems that there is something wrong which causes this code to behave nondeterministically and sometimes wrong.

        final C c = new C("att");
        final B b = new B(List.of(new B.C2(c)));
        final A a = new A(List.of(c), List.of(b));

        a.getCs().forEach(definition -> template.save(definition));
        a.getBs().forEach(definition -> template.save(definition));
        template.save(a);

        final Optional<Map<String, Object>> one = client.query("Match (n{id:'att'})-[r]-(m:A) return count(r)").fetch().one();
        System.out.println(one.get().get("count(r)"));

a has a member cs which includes a C object. However, sometimes a link is created between a and c (thus, printing 1) and sometimes no link is created between them (thus, printing 0).

Just run the code several times and see what is printed.

[meistermeier]

Could you please tell us which version are you using?

Edit: Found the link...nvm.

[meistermeier]

I cannot really reproduce your issue. Always getting the relationship created without any changes to your code.
Speaking of which: you could skip the forEach definition parts because all the cascading relationship and nodes will get persisted during the template.save(a) call.
Maybe you can give me any hints how to enforce the faulty behaviour.

[shayantabrizi]

We have encountered it on three different computers. Windows and Linux. Neo4j 4.3.2 and 4.3.1 (embedded) and 4.2.1 (Neo4j Desktop).

The forEach parts were mentioned for reproducibility. But, I checked and without them the problem persists. I run on 4.2.1 (Neo4j Desktop) now and report the results:
First run: 1
Second run: 1
Third run: 0
Forth run: 1
Fifth run: 0
Sixth run: 0
Seventh run: 1

The results are non-deterministic. Maybe, a 0 happens in your system after several runs.
I committed the code I got the above results with now, in which the forEachs are removed.

[meistermeier]

I can see the problem now. Just re-ran it and at least with a 30/70 ratio it is reproducible.
Investigating...

[meistermeier]

It would be helpful if you could give 6.1.3-GH-2318-SNAPSHOT a try.

<dependency>
    <groupId>org.springframework.data</groupId>
    <artifactId>spring-data-neo4j</artifactId>
    <version>6.1.3-GH-2318-SNAPSHOT</version>
</dependency>

To get the snapshot you would have to add Spring's repositories to your application:

<repositories>
  <repository>
    <id>spring-milestones</id>
    <name>Spring Milestones</name>
    <url>https://repo.spring.io/milestone</url>
    <snapshots>
      <enabled>false</enabled>
    </snapshots>
  </repository>
  <repository>
    <id>spring-snapshots</id>
    <name>Spring Snapshots</name>
    <url>https://repo.spring.io/snapshot</url>
    <releases>
      <enabled>false</enabled>
    </releases>
  </repository>
</repositories>

[shayantabrizi]

It seems that the problem is solved. Thank you.

[meistermeier]

Thanks for your feedback. Will merge this now into 6.1.x for the 6.1.3 patch and main.