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neo4j / neo4j-ogm

Java Object-Graph Mapping Library for Neo4j
https://neo4j.com/docs/ogm-manual/
Apache License 2.0
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The name of a `RelationshipEntity` for a single node relation is limited the relationship name #1132

Closed oxisto closed 3 months ago

oxisto commented 3 months ago

This is a little bit of a complicated issue, but it seems I encounter a somewhat weird behaviour, if one uses RelationshipEntity objects for single-node relationships.

Consider the following (Kotlin) code:

@RelationshipEntity
class AstEdge(@StartNode var start: Node, @EndNode var end: Node) {
    @field:Id @field:GeneratedValue private val id: Long? = null
}

@NodeEntity
class FunctionDeclaration : Node {
  @Relationship("BODY")
  var body = AstEdge()
}

(the real example code is a bit more complex with generics, but the issue still seems to persist with this small example)

When trying to persist this I get the following error:

java.lang.NullPointerException: Cannot invoke "org.neo4j.ogm.metadata.ClassInfo.isAbstract()" because "declaredObjectInfo" is null
    at org.neo4j.ogm.context.EntityGraphMapper.mapEntityReferences(EntityGraphMapper.java:428)
    at org.neo4j.ogm.context.EntityGraphMapper.mapEntity(EntityGraphMapper.java:282)
    at org.neo4j.ogm.context.EntityGraphMapper.mapRelatedEntity(EntityGraphMapper.java:847)
    at org.neo4j.ogm.context.EntityGraphMapper.link(EntityGraphMapper.java:532)
    at org.neo4j.ogm.context.EntityGraphMapper.mapEntityReferences(EntityGraphMapper.java:453)
    at org.neo4j.ogm.context.EntityGraphMapper.mapEntity(EntityGraphMapper.java:282)
    at org.neo4j.ogm.context.EntityGraphMapper.mapRelatedEntity(EntityGraphMapper.java:847)
    at org.neo4j.ogm.context.EntityGraphMapper.link(EntityGraphMapper.java:532)
    at org.neo4j.ogm.context.EntityGraphMapper.mapEntityReferences(EntityGraphMapper.java:453)
    at org.neo4j.ogm.context.EntityGraphMapper.mapEntity(EntityGraphMapper.java:282)
    at org.neo4j.ogm.context.EntityGraphMapper.mapRelatedEntity(EntityGraphMapper.java:847)
    at org.neo4j.ogm.context.EntityGraphMapper.link(EntityGraphMapper.java:532)
    at org.neo4j.ogm.context.EntityGraphMapper.mapEntityReferences(EntityGraphMapper.java:453)
    at org.neo4j.ogm.context.EntityGraphMapper.mapEntity(EntityGraphMapper.java:282)
    at org.neo4j.ogm.context.EntityGraphMapper.mapRelatedEntity(EntityGraphMapper.java:847)
    at org.neo4j.ogm.context.EntityGraphMapper.link(EntityGraphMapper.java:532)
    at org.neo4j.ogm.context.EntityGraphMapper.mapEntityReferences(EntityGraphMapper.java:453)
    at org.neo4j.ogm.context.EntityGraphMapper.mapEntity(EntityGraphMapper.java:282)
    at org.neo4j.ogm.context.EntityGraphMapper.mapRelatedEntity(EntityGraphMapper.java:847)
    at org.neo4j.ogm.context.EntityGraphMapper.link(EntityGraphMapper.java:532)
    at org.neo4j.ogm.context.EntityGraphMapper.mapEntityReferences(EntityGraphMapper.java:453)
    at org.neo4j.ogm.context.EntityGraphMapper.mapEntity(EntityGraphMapper.java:282)
    at org.neo4j.ogm.context.EntityGraphMapper.map(EntityGraphMapper.java:170)
    at org.neo4j.ogm.session.delegates.SaveDelegate.lambda$save$1(SaveDelegate.java:89)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
    at org.neo4j.ogm.session.delegates.SaveDelegate.save(SaveDelegate.java:89)
    at org.neo4j.ogm.session.Neo4jSession.save(Neo4jSession.java:495)

If I change the @Relationship name to ASTEDGE (matching the relationship entity class in uppercase), the graph persists without problems. Persisting a list of such entities with BODY also works.

Expected Behavior

I would expect that the above sample works.

Current Behavior

See stack-trace

meistermeier commented 3 months ago

This is indeed interesting if this should really happen. From what I can see in our test suite this should not be a problem. Could you provide also the information what Node is in your example? It would be also helpful to see the test code that sets up the entities and persist them, to get the full picture.

oxisto commented 3 months ago

This is indeed interesting if this should really happen. From what I can see in our test suite this should not be a problem. Could you provide also the information what Node is in your example? It would be also helpful to see the test code that sets up the entities and persist them, to get the full picture.

Hi! Node ist just a normal base class. I will try to distill a running example from our code base during the day today. The code base is open-source, but it might be too complex to just simply run.

meistermeier commented 3 months ago

This would be very helpful, thanks.

oxisto commented 3 months ago

This would be very helpful, thanks.

I managed to put it together here: https://github.com/oxisto/kotlin-ogm-test Note that this example is a bit more complex (and contains some generics), but it also fails without the generics.

meistermeier commented 3 months ago

From the given example (and sorry that I missed this in the examples above), I can see that this is expected behaviour in Neo4j-OGM. It fails with the NPE because it cannot find the matching definition for the "unknown" relationship type. Without a type / value in the @RelationshipEntity annotation it will fall back to UPPER_SNAKECASE for the naming. The types need to be in sync. While writing and confirming this in code, I figured out that this is partial true: It is just plain upper case. Don't know why this changed. (I am happy to create a new issue for this)

Also see this in the reference documentation: https://neo4j.com/docs/ogm-manual/current/reference/#reference:annotating-entities:relationship-entity

oxisto commented 3 months ago

From the given example (and sorry that I missed this in the examples above), I can see that this is expected behaviour in Neo4j-OGM. It fails with the NPE because it cannot find the matching definition for the "unknown" relationship type. Without a type / value in the @RelationshipEntity annotation it will fall back to UPPER_SNAKECASE for the naming. The types need to be in sync. While writing and confirming this in code, I figured out that this is partial true: It is just plain upper case. Don't know why this changed. (I am happy to create a new issue for this)

Also see this in the reference documentation: https://neo4j.com/docs/ogm-manual/current/reference/#reference:annotating-entities:relationship-entity

That only seems to be partially true because the relationshipType variable is correctly set to BODY if I debug it. Yes you are correct that it fails with an NPE because it cannot find a relationship entity class for this using the metadata/classdata lookup. However, the mapper seems to be "intelligent" enough to see that AstEdge is in fact a relationship entity and if you add an additional null check, things continue normally (see my PR). It seems the only reason the added look-up is here, is to check whether the returned class (which happens to be null) is abstract. Well if its null its never abstract so the normal control flow could continue.

meistermeier commented 3 months ago

is to check whether the returned class (which happens to be null) is abstract

Unfortunately being null as in "I don't know this entity" differs to plain false. What if the class is abstract but not correctly mapped? Additionally, there are other places in the code that are trying to resolve the information of a particular class via Metadata#classInfo and are relying on those information.