How to treat nested entity add/update/delete operations in Hibernate? - spring

Question

I once again joined a project which uses Hibernate (Spring/Hibernate/Kotlin to be exact) and have read through a number of Vlad Mihalcea wonderful articles to refresh my knowledges about this ORM (this article is of my current interest).
What I'm trying to understand is how should I treat add/update/delete operations for nested entities (bidirectional #OneToMany). Here is what I don't understand.
Say we have a Post entity:
#Entity(name = "Post")
#Table(name = "post")
class Post(
#Id
#GeneratedValue
var id: Long? = null,
val title: String,
#OneToMany(mappedBy = "post", cascade = CascadeType.ALL, orphanRemoval = true)
private val comments: MutableList<PostComment> = MutableList<PostComment>()
) {
fun addComment(comment: PostComment) {
comments.add(comment)
comment.post = this
}
fun removeComment(comment: PostComment) {
comments.remove(comment)
comment.post = null
}
}
And a PostComment entity:
#Entity(name = "PostComment")
#Table(name = "post_comment")
class PostComment(
#Id
#GeneratedValue
var id: Long? = null,
val review: String,
#ManyToOne(fetch = FetchType.LAZY)
var post: Post
) {
override fun equals(o: Any?): Boolean {
if (this === o) return true
if (o !is PostComment) false
return id != null && id == o.id
}
override fun hashCode(): Int {
return javaClass.hashCode()
}
}
All in all everything is good, but here is the couple of things I don't know how to cover:
In fact Post class won't compile since I set post field of PostComment to null while it is not nullable. What is a good practice to handle it? Should I make all relations nullable in kotlin just because hibernate require it to be so and it is in contradiction with business logic?
It is more or less clear how to add and delete nested entities, though what should we do if we need to update already existing nested entity. Let's imagine we have a Post(id=1, title="lovely post", comments=[PostComment(id=15, review="good", post=this)] and we get a update action with the following PostDto(id=1, title="not that nice post", comments=[PostComment(id=15, review="bad", post=this)]. As you can see we need to update title for Post and review for PostComment. If we take a look at the Vlad's article I linked above we do not see any update methods. I think it was just ommited since it is not related to article topic.
But I wonder what is the good practice to handle such an update? Something like these two approaches comes to my mind but I'm not sure if these are the best things to do:
#Entity(name = "Post")
#Table(name = "post")
class Post(
//fields...
) {
fun addComment(comment: PostComment) {
comments.add(comment)
comment.post = this
}
fun removeComment(comment: PostComment) {
comments.remove(comment)
comment.post = null
}
// not effective, since issue delete/insert queries, but clean
fun updateComment(comment: PostComment) {
val commentId = comment.id!!
comments.removeIf { it.id == commentId }
comment.team = this
}
// effective, since issue only update query, but dirty as hell
fun updateComment(commentId: Long, review: String) {
val comment = comments.find { it.id == commentId }!!
comment.review = review
}
}
Not actual anymore. Refer good explanation by #Chris in a comment section.
Imagine we need an endpoint to update a comment only. What
is the best way to organise our code base for such a scenario?
Should we always update it like this (always fetch old post, looks
inefficient) or is there any better/efficient approach?
#Transactional
fun reassignComment(newPostId: Long, commentDto: CommentDto) {
val comment = commentRepo.findByIdOrNull(commentDto.id)!!
val oldPost = comment.post
val newPost = postRepo.findByIdOrNull(newPostId)!!
oldPost.removeComment(comment)
newPost.addComment(comment)
}
Thanks anyone for your time and input!