使用jpa持久化（或查找）对象不会保存它封装的对象列表

Question

Suppose that we have in a relational database a table "Book" that is referenced by a table "Page". A book contains one or more pages and a page belongs to a single book.

In JPA this relation is defined as below in the entities classes

class Book:
@OneToMany(mappedBy = "book")
private List<Page> pageList;

class Page:
@JoinColumn(name = "book", referencedColumnName = "id")
@ManyToOne
private Book book;

Now, if I create a Book instance and I set its list of pages with a list of Page entities objets. When I persist the book (see code below), I find that the book is stored in the table Book but the book pages are not saved. Can this be done automatically, ie if I save a book while the pages contained in the book are also saved in the Page table.

Same question for the retrieval of a book, logically when I get a book (use jpa find method) and it encapsulate a list of pages I must have the associated pages in the book instance, but this is not the case.

So what is my fault? or what I'm missing ?

public void add(Book book) throws TestException
{
    try {
        em = getEmf().createEntityManager();
        EntityTransaction tr = em.getTransaction();
        tr.begin();
        em.persist(book);
        tr.commit();
        em.close();
    } catch (PersistenceException pex) {
        throw new TestException(
            "This book already exists.", pex);
    }
}

Answer 1

You need to add @OneToMany(mappedBy = "book", cascade = CascadeType.PERSIST) . For JPA's OneToMany , by default no operations are Cascaded .