1、多对一单向关联
需要在多的一方添加外键关联。比如一个组有多个用户,一个用户属于一个组。
(1)Group.java
package com.yy.hibernate.model; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.Table; @Entity @Table(name="t_group") public class Group { private int id; private String name; @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; } }
(2)User.java
package com.yy.hibernate.model; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.ManyToOne; import javax.persistence.Table; @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; } }
(3)结果
mysql> desc t_group; +-------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(255) | YES | | NULL | | +-------+--------------+------+-----+---------+----------------+
mysql> desc t_user; +----------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(255) | YES | | NULL | | | group_id | int(11) | YES | MUL | NULL | | +----------+--------------+------+-----+---------+----------------+