kotlin delegated field is always null when loaded from hibernate

Question

I'm trying to do something that would be simple as hell in java but kotlin came to make it a nightmare.

interface IChargeableDTO{

    var name: String
    var ref: String
    var priceCents: Int
    var maxInstallments: Int
    var gateway: PaymentGateway
}

@Embeddable
open class ChargeableDTO(
        @field:NotBlank override  var name: String,
        @field:NotBlank override  var ref: String,
        @field:Min(1) override  var priceCents: Int,
        @field:NotNull @field:Min(1) @field:Max(12) override  var maxInstallments: Int = 1,
        @field:NotNull override  var gateway: PaymentGateway) : IChargeableDTO {


@Embeddable
class CreditPackageDTO(name: String,
                       ref: String,
                       priceCents: Int,
                       maxInstallments: Int = 1,
                       gateway: PaymentGateway,
                       @field:Min(1) var creditAmount: Int) : ChargeableDTO(name, ref, priceCents, maxInstallments, gateway) {

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
abstract class ChargeableEntity(@field:Valid @field:Embedded @field:JsonIgnore open var dto: ChargeableDTO) : IChargeableDTO by dto

@Entity
@Table(name = "credit_packages", uniqueConstraints = [UniqueConstraint(columnNames = ["gateway", "ref"])])
class CreditPackage(dto: CreditPackageDTO) :  ChargeableEntity(dto) {

in short terms

I've a dto and a childDto that extends from it...
i've a base entity class which takes dto as constructor parameter and a child entity class that takes the childDto as parameter

when i load the child entity class from database using JPAREPOSITORY... the $$delegateDto IS ALWAYS NULL and then causes null pointer exception

what am i doing wrong?

Answer 1

Just came across this question and had a similar issue that may be worth sharing:

In my case, the backing foo$delegate field for a lazy initialized property was null after the entity was created. Also, @Transient fields were not initialized correctly.

It turned out that it was caused by missing default constructors within the entity inheritance chain (I used the kotlin-noarg plugin so JPA was working fine in general).

Potential Solution:

Add default values for the dto parameters in ChargeableEntity and CreditPackage (and possibly also for the DTO constructors).

Not sure if this the complete solution, but it seems to be a necessary condition.