NullCollectionEvent is triggered for entities that use the Bytecode Enhancement lazy loading

[DawidStuzynski]

Hi, I am using Kotlin + Quarkus 3.5.0 with Hypersistence Optimizer I have something similar in my app @OneToMany(mappedBy = "someId", cascade = [PERSIST, REMOVE], fetch = LAZY) val enities: MutableSet<ChildEntity> = mutableSetOf() but after test it using Hypersistence Optimizer I got a NullCollectionEvent on this element, is it something related to Kotlin or Quarkus?

[vladmihalcea]

It could be a false positive in Hypersistence Optimizer due to the differences between Kotlin and Java. Hypersistence Optimizer is built and tested using Java, and it can work with Kotlin, but there might be some issues that need to be addressed.

I will try to build an example using your mapping and see if I can replicate it.

[DawidStuzynski]

After deeper investigation I found out that it only takes place if primary constructor of entity is not empty

@Entity
class ParentEntity(
    val stringField: String
) {

    @Id
    @SequenceGenerator(name = "parent_entity_sq", sequenceName = "parent_entity_sq", allocationSize = 50)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "parent_entity_sq")
    var id: Long? = null

    @OneToMany(mappedBy = "parentEntity", cascade = [CascadeType.PERSIST], fetch = FetchType.LAZY)
    val entities: MutableSet<ChildEntity> = mutableSetOf()

    fun addEntity(entity: ChildEntity) {
        entities.add(entity)
        entity.parentEntity = this
    }

    fun removeEntity(entity: ChildEntity) {
        entities.remove(entity)
        entity.parentEntity = null
    }
}

@Entity
class ChildEntity(

    val field: String,

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "parent_entity_id")
    var parentEntity: ParentEntity? = null
) {

    @Id
    @SequenceGenerator(name = "child_entity_sq", sequenceName = "child_entity_sq", allocationSize = 50)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "child_entity_sq")
    var id: Long? = null
    override fun toString(): String {
        return "ChildEntity(field='$field', id=$id)"
    }
}

here is example of mapping I made In one of my test projects I also made branch with little reproducer, you can find it here: https://github.com/DawidStuzynski/hibernate-quarkus-batching-issue/tree/hypersistence-optimizer-null-event

[vladmihalcea]

Thanks for the replicating test case. I'll debug it through.

[vladmihalcea]

@DawidStuzynski I debugged the example, and the issue is generated by the Hibernate bytecode enhancement mechanism which allows the attribute to be null as the initialization will happen upon calling the getter for the very first time.

I will fix this issue and release it in the 2.8 version which will be released soon.

[vladmihalcea]

Fixed.