Hibernate lazy relations are fetched n+1 without properties being called - Kotlin - postgresql

Question

I am using hibernate and doing a simple query to select all of a given entity. I only want the entity and not its relations. However hibernate does fetch the relations and the relations of the relations, in a n+1 manner.
It's a Spring Boot application and written in Kotlin.
The relations are annotated with FetchType.LAZY and the query i'm doing looks like so:
entityManager.createQuery("SELECT a FROM Apartment a")
.resultList
This is the only code that i am calling and i do NOT even return the results from the controller, so it is not some serialization library that calls the lazy properties.
These are the entities:
#Entity
class Apartment(
#Id
private val id: String,
private val heading: String,
#ManyToOne(fetch = LAZY)
private val building: Building
)
#Entity
class Building(
#Id
private val id: String,
private val heading: String,
#ManyToOne(fetch = FetchType.LAZY)
private val owner: User
)
#Entity
#Table(name="users")
class User(
#Id
private val id: String,
private val email: String
)
I have turned on hibernate query logging, and when i run the query above it looks like:
Fetch all apartments
Fetch buildings for apartment 1
Fetch users for building 1
fetch buildings for apartment 2
fetch users for building 2
....
I have created a git repository that reproduces the problem: https://github.com/Herlevsen/hibernate-lazy-fetch-repoduction
It comes setup with a docker-compose file that launches a postgres database, and the application automatically creates the schema and creates some dummy data on startup. So it's fairly easy to get up and running.
I'm really hoping someone can tell me what's going on.
Thanks!

Answer 1

You have to open the entity classes. Hibernate requires open classes to create proxies to support LAZY - ManyToOne fields:
#Entity
open class Apartment(
#Id
private val id: String,
private val heading: String,
#ManyToOne(fetch = LAZY)
private val building: Building
)
#Entity
open class Building(
#Id
private val id: String,
private val heading: String,
#ManyToOne(fetch = FetchType.LAZY)
private val owner: User
)
#Entity
#Table(name="users")
open class User(
#Id
private val id: String,
private val email: String
)
You can also use the all-open-Plugin.