hibernate-annotation CascadeType.PERSIST不起作用的解决方法

有如下两个实体类 ， Student和Grade 为多对一关系。

Student.java

 @Entity
 public class Student {
     private Integer id;
     private String name;
     private Grade grade;
     @Id
     @GeneratedValue(strategy=GenerationType.AUTO)
     public Integer getId() {
         return id;
     }
     public void setId(Integer id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     @ManyToOne(cascade={CascadeType.PERSIST})
     @JoinColumn(name="gradeid")
     public Grade getGrade() {
         return grade;
     }
     public void setGrade(Grade grade) {
         this.grade = grade;
     }

 }

Grade.java

 @Entity
 public class Grade {

     private Integer id;
     private String name;

     @Id
     @GeneratedValue(strategy=GenerationType.AUTO)
     public Integer getId() {
         return id;
     }
     public void setId(Integer id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }

 }

可以看到Student类的grade属性已经设置了   @ManyToOne(cascade={CascadeType.PERSIST})

但只save Student对象时依然会报 org.hibernate.TransientObjectException 异常,如下：

public class Init {
    public static void main(String[] args) {
        Session session = HibernateUtil.getSessionFactory().getCurrentSession();
        session.beginTransaction();

        Grade g = new Grade();
        g.setName("一班");

        Student s = new Student();
        s.setName("张三");
        s.setGrade(g);

        session.save(s);

        session.getTransaction().commit();

    }
}

运行结果：

Exception in thread "main" org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: accp.hib.Grade

解决办法如下：

方法一：改用persist方法来保存

把session.save(s); 更改为 session.persist(s);

再次保存成功。

Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: insert into Grade (name, id) values (?, ?)
Hibernate: insert into Student (gradeid, name, id) values (?, ?, ?)

方法二：使用hibernate的自定义的级联，不要使用jpa的

把Student类grade的注解改为hibernate的注解

@ManyToOne(cascade={CascadeType.PERSIST})
@JoinColumn(name="gradeid")

改为:

@ManyToOne

@JoinColumn(name="gradeid")

@Cascade(value={CascadeType.SAVE_UPDATE})

注意，这里的CascadeType和@Cascade都是org.hibernate.annotations包下的，所以把

import javax.persistence.CascadeType;

改为：import org.hibernate.annotations.CascadeType;

并加上：import org.hibernate.annotations.Cascade;

再次保存成功。