（），对象仍标记为未保存的瞬态的实例

Question

Library lib; //has a OneToMany rs to Book 
lib = new Library(); 

Book book; //has a OneToMany rs to Letters 
book = new Book(lib); 
book.save() 

book = new Book(lib); 
book.merge() //.save() will throw an exception (detached entity passed to persist jpa) because of lib, so I merge it 

Letters letters; 
letters = new Letters(book); 
letters.save(); //throws TransientPropertyValueException: object references an unsaved transient instance. 

出于测试目的，我想创建使用相同的库多本图书，并将它们保存。另外我想创建多个字母，使用同一本书并存储它们。但我不知道如何实现这一点，因为合并后的（书），这本书不再瞬态..

感谢

编辑：增加了额外的类使事情变得更加清晰。

public abstract class Model implements Serializable { 
/** 
* Save the current object in the database. 
* 
*/ 
public void save() { 
    EntityManager entityManager = HibernateUtil.getEntityManagerFactory().createEntityManager(); 
    entityManager.getTransaction().begin(); 
    entityManager.persist(this); 
    entityManager.getTransaction().commit(); 
    entityManager.close(); 
} 
/** 
* Delete the current object from the database. 
* 
*/ 
public void delete() { 
    EntityManager entityManager = HibernateUtil.getEntityManagerFactory().createEntityManager(); 
    entityManager.getTransaction().begin(); 
    entityManager.remove(entityManager.contains(this) ? this : entityManager.merge(this)); 
    entityManager.getTransaction().commit(); 
    entityManager.close(); 
} 

public void merge(){ 
    EntityManager entityManager = HibernateUtil.getEntityManagerFactory().createEntityManager(); 
    entityManager.getTransaction().begin(); 
    entityManager.merge(this); 
    entityManager.getTransaction().commit(); 
    entityManager.close(); 
} 
} 

Book实体（Letter和图书馆实体看起来是一样的）

@Entity 
@Table(name = "book") 
public class Book{ 

@Id 
@GeneratedValue(strategy = GenerationType.IDENTITY) 
@Column(name = "BOOK_ID") 
private Integer id; 

@OneToMany(fetch = FetchType.LAZY, mappedBy = "book", cascade = {CascadeType.ALL}) 
private List<Letters> letters; 

@ManyToOne(fetch = FetchType.LAZY,cascade = {CascadeType.ALL}) 
@JoinColumn(name = "lib_id") 
Library library; 

}

Answer 1

什么@JBNizet正打算说的是，你需要develop better your question, make it clearer！

关于你的问题，我想你有类似的实体结构：

实体图书馆：

@Entity 
@Table(name = "library") 
public class Library { 

    @Id 
    @GeneratedValue(strategy = GenerationType.IDENTITY) 
    @Column(name = "LIB_ID") 
    private Integer id; 

    @OneToMany(mappedBy = "library") 
    private List<Book> books; 

    // getters & setters 
} 

实体书：

@Entity 
@Table(name = "book") 
public class Book { 

    @Id 
    @GeneratedValue(strategy = GenerationType.IDENTITY) 
    @Column(name = "BOOK_ID") 
    private Integer id; 

    @ManyToOne 
    @JoinColumn(name = "LIB_ID") 
    private Library library; 

    @OneToMany(mappedBy = "book") 
    private List<Letters> letters; 

    // ... 
} 

实体快报：

@Entity 
@Table(name = "letters") 
public class Letters { 

    @Id 
    @GeneratedValue(strategy = GenerationType.IDENTITY) 
    @Column(name = "LETTERS_ID") 
    private Integer id; 

    @ManyToOne 
    @JoinColumn(name = "BOOK_ID") 
    private Book book; 

    // ... 

} 

这个问题通常与缺乏的cascade=CascadeType.ALL您@ManyToOne映射，已经here说明。

但是，一旦你打开一个会话，保存/合并每个对象，然后提交/关闭它，你必须改变你的关系的级联类型。这样做：

• 保持library对象的级联类型的书类中为@ManyToOne(fetch = FetchType.LAZY, cascade = { CascadeType.ALL })
• 更改所有其他级联到CascadeType.MERGE。这样，每次JPA必须保存整个对象树时，它总会尝试合并它们。