Possibly support @Transient fields for Kotlin data classes without separate persistence constructor

[pmaedel]

The necessity to provide a separate persistence constructor for kotlin data classes with @Transient properties seems odd to me.

data class Fruit(
    @Id
    val id: Long? = null,
    val treeId: Long,
    val ripeness: Ripeness,
    @Transient
    val joinedTree: Tree? = null
) {

    @PersistenceConstructor
    constructor(
        id: Long?,
        treeId: Long,
        ripeness: Ripeness
    ) : this(
        id = id,
        treeId = treeId,
        ripeness = ripeness,
        joinedTree = null
    )
}

I would think it should be possible to exclude a @transient field during mapping for which default value is defined?

[mp911de]

Thanks for raising a ticket. Improving @Transient property handling for constructor properties is indeed worth considering. Until that's in place, we should add @Value support so the object creation can spawn a null value which removes the need for an additional persistence constructor. See #450.

[mp911de]

We discussed the issue with our team and concluded that opening persistence constructors for transient properties contributes to ambiguity. The strict behavior allows for exact reasoning what's happening. Language features such as Kotlin's defaulting mechanism allow for graceful defaults. For now, we recommend using @Value("null").