How do I put JPA annotations on delegated properties in Kotlin? - kotlin

Question

So let's say I have a JPA entity like
#Entity
#Table(name = "plasmid_reference")
class PlasmidReference {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
var id: Int? = null
#Column(name = "project_id")
var projectId: Int? = null
#Column(name = "plasmid_id")
var plasmidId: Int? = null
}
Now, I know that for each and every entry in the plasmid_reference join table none of these properties will be nullable. (In fact, the database enforces this.)
How can I tell Kotlin?
A naive approach would be to try with lateinit...
#Entity
#Table(name = "plasmid_reference")
class PlasmidReference {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
lateinit var id: Int
#Column(name = "project_id")
lateinit var projectId: Int
#Column(name = "plasmid_id")
lateinit var plasmidId: Int
}
This does not even compile.
'lateinit' modifier is not allowed on properties of primitive types
Fine, let's go with the suggested solution and convert to using delegates.
#Entity
#Table(name = "plasmid_reference")
class PlasmidReference {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
var id by notNull<Int>()
#Column(name = "project_id")
var projectId by notNull<Int>()
#Column(name = "plasmid_id")
var plasmidId by notNull<Int>()
}
This still does not compile because
This annotation is not applicable to target 'member property with delegate'
ok ... that sounds like a kotlin thing and in Java, I would toss the annotation on a field, so maybe ...
#Entity
#Table(name = "plasmid_reference")
class PlasmidReference {
#field:Id
#field:GeneratedValue(strategy = GenerationType.IDENTITY)
var id by notNull<Int>()
#field:Column(name = "project_id")
var projectId by notNull<Int>()
#field:Column(name = "plasmid_id")
var plasmidId by notNull<Int>()
}
No, it turns out, not really. Still does not compile because
'#field:' annotations could be applied only to properties with backing fields
Fine, so let's annotate "the field storing the delegate instance for a delegated property" (cf. https://kotlinlang.org/docs/reference/annotations.html#annotation-use-site-targets )
#Entity
#Table(name = "plasmid_reference")
class PlasmidReference {
#delegate:Id
#delegate:GeneratedValue(strategy = GenerationType.IDENTITY)
var id by notNull<Int>()
#delegate:Column(name = "project_id")
var projectId by notNull<Int>()
#delegate:Column(name = "plasmid_id")
var plasmidId by notNull<Int>()
}
This DOES compile but will throw a runtime exception because
The attribute [plasmidId] is not present in the managed type [EntityTypeImpl#960932033:PlasmidReference
[ javaType: class com.[...].PlasmidReference descriptor: RelationalDescriptor(com.[...].PlasmidReference --> [DatabaseTable(plasmid_reference)]), mappings: 3]].
at org.eclipse.persistence.internal.jpa.metamodel.ManagedTypeImpl.getAttribute(ManagedTypeImpl.java:151)
at org.springframework.data.jpa.repository.query.QueryUtils.toExpressionRecursively(QueryUtils.java:635)
Aaaaaand I'm out of ideas.
How do I resolve this?

Answer 1

Moving it to the constructor definition should do the trick
#Entity
#Table(name = "plasmid_reference")
class PlasmidReference(
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
var id: Int? = null,
#Column(name = "project_id")
var projectId: Int,
#Column(name = "plasmid_id")
var plasmidId: Int
)