Setting autogenerated Id manually in Hibernate

README.md

Setting auto-generated Ids manually with Hibernate

In this tutorial, you will learn how to implement a custom IdentifierGenerator to support auto-generated and manually assigned Ids using Hibernate.

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UuidGenerator.kt

package com.matchilling.lib.hibernate

import org.hibernate.engine.spi.SharedSessionContractImplementor
import org.hibernate.id.IdentifierGenerator
import java.io.Serializable
import java.util.*
import kotlin.reflect.full.declaredMemberProperties
import kotlin.reflect.jvm.javaType

class UuidGenerator : IdentifierGenerator {

    override fun generate(
            session: SharedSessionContractImplementor?,
            instance: Any?
    ): Serializable {
        val id = instance!!::class.declaredMemberProperties.find {
            it.name == "id" && it.returnType.javaType.typeName == UUID::class.java.canonicalName
        }?.getter?.call(instance)

        return if (id != null) {
            id as UUID
        } else {
            UUID.randomUUID()
        }
    }

    companion object {
        const val NAME = "uuid"
        const val STRATEGY = "com.matchilling.lib.hibernate.UuidGenerator"
    }
}

UuidGeneratorTest.kt

package com.matchilling.lib.hibernate

import io.mockk.mockk
import org.hibernate.engine.spi.SharedSessionContractImplementor
import org.junit.Test
import org.junit.jupiter.api.Assertions.assertEquals
import java.util.*

internal class UuidGeneratorTest {

    private val subject = UuidGenerator()

    private val uuid = Regex("[0-9a-fA-F]{8}(?:-[0-9a-fA-F]{4}){3}-[0-9a-fA-F]{12}")

    internal class EntityImpl(val id: UUID?)

    @Test
    fun `should assign a random UUID if id prop is null`() {
        // given
        val instance = EntityImpl(id = null)

        // and
        val session = mockk<SharedSessionContractImplementor>()

        // when
        val id = subject.generate(session, instance)

        // then
        assert(id.toString().matches(uuid))
    }

    @Test
    fun `should not generate a new UUID when id prop is not null`() {
        // given
        val expected = UUID.fromString("d1f1ece1-c84b-465f-9529-0c3820c0c2d7")

        // and
        val instance = EntityImpl(id = expected)

        // and
        val session = mockk<SharedSessionContractImplementor>()

        // when
        val actual = subject.generate(session, instance)

        // then
        assertEquals(expected, actual)
    }
}