hibernate学习：级联查询

一：看例子

二：知识点

org.hibernate.TransientObjectException: object references an unsaved transient instance -
save the transient instance before flushing: com.hibernate.model.UserGroup

User u = new User();
u.setName("liuyanliang");

UserGroup g = new UserGroup();
g.setName("haha");

u.setGroup(g);
Session session = factory.getCurrentSession();
session.beginTransaction();
session.save(u);
session.getTransaction().commit();

默认情况下，save user的时候，不会自动关联user跟group的关系
需要在映射关系中加上级联操作


@ManyToOne(cascade = CascadeType.ALL)
private UserGroup group;

默认不产生任何级联
CascadeType.ALL
CascadeType.MERGE
CascadeType.PERSISTENCE
CascadeType.REFRESH
CascadeType.REMOVE