Spring boot Foreign key constraint fails - spring-boot

Question

so I have a class Observer which needs to have a list of notifications I am using a OneToMany relation between the two classes, but for some reason when I want to insert a notification I get a foreign key constraint failure. I would greatly appreciate it if someone could help me or point me in the right direction, Thanks in advance
Observer class
#Entity
abstract class Observer {
#Id
#GeneratedValue
open var id: Long = -1;
#OneToMany
open var notifications: MutableList<Notification> = mutableListOf()
abstract fun update(podcast: Podcast);
}
// different file
#Entity
class User(
var name: String,
var password: String,
#OneToMany
var podcasts : MutableList<PodcastInfo> = mutableListOf(),
) : Observer() {
override fun update(podcast: Podcast) {
val notification = Notification(message = "There is a new episode of ${podcast.name}");
this.notifications.add(notification)
print("new episode for podcast ${podcast.name}")
}
}
Notification class
#Entity
class Notification(
#Id
#GeneratedValue
val id : Long = -1,
val date : LocalDateTime = LocalDateTime.now(),
val seen : Boolean = false,
val message: String
) {
}
The project is about podcasts and when a new episode is added I want to notify the observers
fun addEpisode(#ModelAttribute episodeRequest : EpisodeRequest, #PathVariable("id") id: Long) : String {
....
podcast.addEpisode(episode); // this line adds the notification to the observer
podcast.updateObservers(observerService)
...
}
// different file
fun updateObservers(observerService: ObserverService){
this.observers.forEach{observer -> observerService.updateObserver(observer) }
}
// different file, this is the only descendant of the observer class
fun updateObserver(observer: Observer) : Observer{
val notifications = mutableListOf<Notification>()
for (notification: Notification in observer.notifications){
notifications.add(notificationService.update(notification))
}
observer.notifications = notifications;
return observerService.save(observer)
}
// different file
fun update(notification: Notification) : Notification {
return notificationRepository.save(notification) // this line throws the error
}
So I thought since I am first inserting/updating the notifications and then updating the observer class, I wouldn't get the foreign key error since the notifications would have valid id's.
java.sql.SQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (podcasts.observer_notifications, CONSTRAINT FKgw8m1isyux27iyu8m0l57kdd6 FOREIGN KEY (notifications_id) REFERENCES notification (id))

Answer 1

You can either use #OneToMany(cascade = CascadeType.MERGE), so that notifications are flushed properly before the observer, or you invoke notificationRepository.flush() right after saving the notifications e.g. use:
fun updateObserver(observer: Observer) : Observer{
val notifications = mutableListOf<Notification>()
for (notification: Notification in observer.notifications){
notifications.add(notificationService.update(notification))
}
entityManager.flush(); // <--- This here
observer.notifications = notifications;
return observerService.save(observer)
}