Hibernate_一对多_多对一_双向关联

在双方都设置对方对象的引用。由于是双向关联，则必须用mappedBy。在一的那方设置mappedBy表示数据库中是以多的那方设置一个外键。具体代码如下

 

Group代码

@Entity
@Table(name="t_group")
public class Group {
	private int id;
	private String name;
	private Set<User> users=new HashSet<User>();
	
	@OneToMany(mappedBy="group")
	public Set<User> getUsers() {
		return users;
	}
	public void setUsers(Set<User> users) {
		this.users = users;
	}
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
}

User代码

@Entity
@Table(name="t_user")
public class User {
	private int id;
	private String name;
	private Group group;
	
	@ManyToOne
	public Group getGroup() {
		return group;
	}
	public void setGroup(Group group) {
		this.group = group;
	}
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}

}