Is #ManyToOne's "optional" param automatically set using Kotlin's nullability - spring

Question

I read that specifying optional = false in the #ManyToOne association annotation could help Spring improve the performance of the queries.
In a Kotlin data class entity, do I actually need to specify the parameter in the annotation, or can Spring figure this out by itself using the nullability of the item field?
For instance, if I have the following declaration:
#Entity
#Table(name = ACCESS_LOGS_ARCHIVES_TABLE, indexes = [
Index(name = "access_logs_archives_item_idx", columnList = "access_item_id")
])
data class AccessLogArchive(
val date: LocalDate,
#ManyToOne(optional = false)
#JoinColumn(name = "access_item_id", nullable = false)
val item: AccessLogItem,
val occurrences: Int
) {
#Id
#GeneratedValue
var id: Long? = null
}
#Entity
#Table(name = ACCESS_ITEMS_TABLE)
data class AccessLogItem(
#Column(length = 3) val code: String,
#Column(columnDefinition = "text") val path: String,
#Column(length = 10) val verb: String
) {
#Id
#GeneratedValue
var id: Long? = null
}
In this case, I would for instance expect Spring to know that the item field is not nullable, and thus the relationship should be understood as optional=false even without specifying it as I did. Is this the case?
Same question goes for the #JoinColumn's nullable = false, by the way.

Answer 1

Consider a simple entity like a Room which has a #ManyToOne relationship to House.
#Entity
class Room(
#ManyToOne(optional = true)
val house: House
) {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
val id: Long = 0
}
JPA will create a room table with a column
`house_id` bigint(20) DEFAULT NULL
If you specify #ManyToOne(optional = false)
the column will look like this:
`house_id` bigint(20) NOT NULL
By specifiying optional you tell JPA how the schema should be generated, whether the column can be NULL or not.
At runtime trying to load a Room without a House will cause an Exception if the house property is not nullable (House instead of House?) even when value of optional is true.
The same applies to #JoinColumn.
Is #ManyToOne's “optional” param automatically set using Kotlin's
nullability?
No it is not. It is independent from that and by default set to true.
Conclusion: In order for you schema to reflect your entities it is a good idea to use optional = true if the house property would be nullable and optional = false if the house property would be non-nullable.