Need to serializable entity on kotlin

Question

I have sombe BaseEntity

import org.springframework.data.util.ProxyUtils
import javax.persistence.GeneratedValue
import javax.persistence.GenerationType
import javax.persistence.Id
import javax.persistence.MappedSuperclass

@MappedSuperclass
abstract class BaseEntity<T>  {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    var id: T? = null

    override fun equals(other: Any?): Boolean {
        other ?: return false

        if (this === other) return true

        if (javaClass != ProxyUtils.getUserClass(other)) return false

        other as BaseEntity<*>

        return this.id != null && this.id == other.id
    }

    override fun hashCode() = 25

    override fun toString(): String {
        return "${this.javaClass.simpleName}(id=$id)"
    }
}

And i have error message, but project are starting.

Class 'T' should implement 'java.io.Serializable'

I've heard that hibernate needs it. But I don't understand why he needs it. And I don't understand how I can do serialization of T

Answer 1

I fixed the problem by simply adding Serializable to type T.

BaseEntity<T: Serializable>

But I did not find out the reason for this error.

@MappedSuperclass
abstract class BaseEntity<T: Serializable>  {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    var id: T? = null

    override fun equals(other: Any?): Boolean {
        other ?: return false

        if (this === other) return true

        if (javaClass != ProxyUtils.getUserClass(other)) return false

        other as BaseEntity<*>

        return this.id != null && this.id == other.id
    }

    override fun hashCode() = 25

    override fun toString(): String {
        return "${this.javaClass.simpleName}(id=$id)"
    }
}