Track state of objects with assigned ids correctly.

[LGDOI]

I cannot tell if is a bug or a feature.

Given two node classes Application and Workflow. Application has outgoing 1-to-many relationship to Workflow.
Workflow has incoming relationship to Application.

The following code causes NPE during .saveAll call.

  @Test
  fun npe() {
    val app1 = Application()
    val wf1 = Workflow()
    val wf2 = Workflow()

    wf1.application = app1 // <===== Comment out to avoid NPE
    wf2.application = app1 // <===== Comment out to avoid NPE

    app1.workflows = listOf(wf1, wf2)
    applicationRepository.saveAll(listOf(app1))
  }

Note: if you comment out these two lines setting app1 to wf1 and wf2, NPE won't occur.
Note2: replace .saveAll(listOf(app1)) with .save(app1) solves the problem.
Note3: this example only shows one app1. but the same NPE happens even if the list size > 1

Stacktrace

java.lang.NullPointerException
	at org.springframework.data.neo4j.core.mapping.NestedRelationshipProcessingStateMachine$RelationshipDescriptionWithSourceId.equals(NestedRelationshipProcessingStateMachine.java:133)
	at java.base/java.util.HashMap.putVal(HashMap.java:630)
	at java.base/java.util.HashMap.put(HashMap.java:607)
	at java.base/java.util.HashSet.add(HashSet.java:220)
	at org.springframework.data.neo4j.core.mapping.NestedRelationshipProcessingStateMachine.markRelationshipAsProcessed(NestedRelationshipProcessingStateMachine.java:154)
	at org.springframework.data.neo4j.core.Neo4jTemplate.lambda$processNestedRelations$25(Neo4jTemplate.java:772)
	at org.springframework.data.mapping.model.BasicPersistentEntity.doWithAssociations(BasicPersistentEntity.java:387)
	at org.springframework.data.neo4j.core.Neo4jTemplate.processNestedRelations(Neo4jTemplate.java:658)
	at org.springframework.data.neo4j.core.Neo4jTemplate.lambda$processNestedRelations$25(Neo4jTemplate.java:801)
	at org.springframework.data.mapping.model.BasicPersistentEntity.doWithAssociations(BasicPersistentEntity.java:387)
	at org.springframework.data.neo4j.core.Neo4jTemplate.processNestedRelations(Neo4jTemplate.java:658)
	at org.springframework.data.neo4j.core.Neo4jTemplate.processRelations(Neo4jTemplate.java:649)
	at org.springframework.data.neo4j.core.Neo4jTemplate.lambda$saveAllImpl$14(Neo4jTemplate.java:482)
... more

Analysis

Neo4jTemplate.processNestedRelations contains a lambda there is a condition to set relatedInternalId on line 746-747.

if (stateMachine.hasProcessedValue(relatedValueToStore)) {
  relatedInternalId = stateMachine.getInternalId(relatedValueToStore);

When this condition is true, stateMachine.getInternalId(relatedValueToStore); return null.

Question

Should this condition return false if the stateMachine does not have an internal ID for relatedValueToStore?

[michael-simons]

Hi @LGDOI Are you able to share the classes for Application and Workflow? I am not able to reproduce this.

Also are you using 6.1.x or 6.0.x?

[michael-simons]

Never mind, I could figure out what I needed to reproduce it from your other ticket.

[LGDOI]

Hi, @michael-simons,
Thank you for looking into this. So, this issue is related to other issue and will be fixed as part of other bug fix?

I believe I was on 6.1.3 when I saw this error (99.9%). But 0.1% chance I was on older version as I was switching b/w version to compare the API behavior.

Edit:

I just realized that you mentioned about 9ed7557. Thank you so much.

[michael-simons]

You're welcome and sorry for any inconvenience. Both reports have been very useful to us.