entityManager.remove() VS JPQL DELETE Query
I know that one side of relation is owner and the other side, marked with mapped by, is non-owner.
Relation is saved in Database with persistence of owner and removed with removal of it. I know that removal of non-owner side will not erase relation. see this link
So far so good.
In my experience, removal on non-owner with JPQL query, removes relation too. It's not clear for me why!? Is there any persuasive explanation?
Code snippets below show my test cases with concept:
Non-Owner
@Entity
public class Book {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String title;
@ManyToMany(mappedBy = "books")
private Set<Author> authors;
}
Owner:
@Entity
public class Author {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String name;
@ManyToMany
private Set<Book> books;
}
Test 1
public void persistingRelationOwnerPersistsRelationSuccessfully(){
Book book = new Book("nonOwner");
entityManager.persist(book);
Author author = new Author("owner", new HashSet<>(Arrays.asList(book)));
entityManager.persist(author);
entityManager.flush();
}
Log:
Hibernate: insert into book (title, id) values (?, ?)
Hibernate: insert into author (name, id) values (?, ?)
Hibernate: insert into author_books (authors_id, books_id) values (?, ?)
Test 2
public void removingRelationOwnerRemovesRelationSuccessfully(){
//persist book and author
entityManager.remove(author);
entityManager.flush();
}
Log:
Hibernate: insert into book (title, id) values (?, ?)
Hibernate: insert into author (name, id) values (?, ?)
Hibernate: insert into author_books (authors_id, books_id) values (?, ?)
Hibernate: delete from author_books where authors_id=?
Hibernate: delete from author where id=?
Test 3
public void removingNonOwnerWillThrowException(){
//persist book and author
entityManager.remove(book);
entityManager.flush();
}
Log: (As Expected)
Hibernate: insert into book (title, id) values (?, ?)
Hibernate: insert into author (name, id) values (?, ?)
Hibernate: insert into author_books (authors_id, books_id) values (?, ?)
Hibernate: delete from book where id=?
javax.persistence.PersistenceException: org.hibernate.exception.ConstraintViolationException: could not execute statement
Test 4
public void removingNonOwnerWithQueryWillRemoveRelation(){
//persist book and author
Query query = entityManager.createQuery("delete from Book b where b.title = 'nonOwner'");
System.out.println("affectedRows = " + query.executeUpdate());
}
Log: (Unexpected behavior)
Hibernate: insert into book (title, id) values (?, ?)
Hibernate: insert into author (name, id) values (?, ?)
Hibernate: insert into author_books (authors_id, books_id) values (?, ?)
Hibernate: delete from author_books where (books_id) in (select id from book where title='nonOwner')
Hibernate: delete from book where title='nonOwner'
affectedRows = 1
