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。