Example entity with composite key Spring Boot and Kotlin

Property.kt

// This will not serialize!
data class Muppet(val name: String)

// This will serialize!
data class Puppet(val name: String = "")

// Composite key class must implement Serializable
// and have defaults.
class PropertyId(
        val uuid: UUID = UUID.randomUUID(),
        val name: String = "") : Serializable

// Need defaults everywhere!
@Entity
@IdClass(PropertyId::class)
data class Property(
        @Id val uuid: UUID = UUID.randomUUID(),
        @Id val name: String = "",
        val value: String = "")

Thank you, this was very helpful. Glad I found dug to the 2nd page of google and found this.

Works like a charm 🍸
Thank you

I almost did set all those awful default values like in your example - but then I found the official Kotlin Docs recommending the JPA compiler plugin which generates the no-arg constructors for you! I think THAT is the way to go and worked perfectly fine for me: https://kotlinlang.org/docs/reference/compiler-plugins.html#jpa-support

To add to what @mineralf said, the Kotlin JPA plugin needs a small hint to create that no-arg constructor. I found that I needed to add @Embeddable to the data class to get it to work.

@Embeddable
data class PropertyId(
        val uuid: UUID,
        val name: String) : Serializable