java - @ElementCollection 是否意味着 orphanRemoval？

Question

根据这篇文章Difference between @OneToMany and @ElementCollection?我应该更喜欢 @ElementCollection 用于可嵌入类型，而 @OneToMany 用于实体。但是使用 @OneToMany 我可以额外设置选项 orphanRemoval=true。我如何使用 @ElementCollection 执行此操作？它暗示了吗？

Answer 1

这是隐含的。删除拥有实体也会删除 @ElementCollection 上的所有数据。如果 Session 尚未关闭，则将 Collection 设置为 null 或更改 Collection 中的元素将导致更新。

官方文档here是这样说的:

2.8.1. Collections as a value type

Value and embeddable type collections have a similar behavior assimple value types because they are automatically persisted whenreferenced by a persistent object and automatically deleted whenunreferenced. If a collection is passed from one persistent object toanother, its elements might be moved from one table to another.
...
For collections of value types, JPA 2.0 defines the @ElementCollectionannotation. The lifecycle of the value-type collection is entirelycontrolled by its owning entity.

我运行了这三个测试来测试它:

  @Test
  public void selectStudentAndSetBooksCollectionToNull() {
    Student student = studentDao.getById(3L);
    List<String> books = student.getBooks();

    books.forEach(System.out::println);

    student.setBooks(null);

    em.flush(); // delete from student_book where student_id = ?
  }

  @Test
  public void selectStudentAndAddBookInCollection() {
    Student student = studentDao.getById(3L);
    List<String> books = student.getBooks();

    books.add("PHP Book");

    books.forEach(System.out::println);

    em.flush(); // insert into student_book(student_id, book) values(?, ?)
  }

  @Test
  public void selectStudentAndChangeCollection() {
    Student student = studentDao.getById(3L);
    List<String> newBooks = new ArrayList<>();

    newBooks.add("Rocket Engineering");

    newBooks.forEach(System.out::println);

    student.setBooks(newBooks);

    em.flush(); // delete from student_book where student_id = ?
    // insert into student_book(student_id, book) values(?, ?)
  } 

这是学生类:

@Entity
@Table(name = "student")
public class Student {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  @Column(name = "student_id", nullable = false, insertable = false, updatable = false)
  private Long id;

  @Column(name = "name", nullable = false)
  private String name;

  @ElementCollection
  @CollectionTable(
      name = "student_books",
      joinColumns = @JoinColumn(name = "student_id", referencedColumnName = "student_id"))
  @Column(name = "book")
  private List<String> books = new ArrayList<>();

  // Getters & Setters

}