一个组有多个用户,一个用户只能属于一个组。
使用Annotation注解来实现多对一单项关联
Group.java:
User.java:
在hibernate.cfg.xml中配置:
建表语句:
alter table t_user
drop
foreign key FKCB63CCB61AEE691B
drop table if exists t_group
drop table if exists t_user
create table t_group (
id integer not null auto_increment,
name varchar(255),
primary key (id)
)
create table t_user (
id integer not null auto_increment,
name varchar(255),
group_id integer,
primary key (id)
)
alter table t_user
add index FKCB63CCB61AEE691B (group_id),
add constraint FKCB63CCB61AEE691B
foreign key (group_id)
references t_group (id)
schema export complete
使用Annotation注解来实现多对一单项关联
Group.java:
package cn.edu.hpu.many2one; 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; } }
User.java:
package cn.edu.hpu.many2one; 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 //核心语句 //@JoinColumn(name="groupid")想改属性名用这个(默认的是group_id) 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; } }
在hibernate.cfg.xml中配置:
<mapping class="cn.edu.hpu.many2one.Group"/> <mapping class="cn.edu.hpu.many2one.User"/>
建表语句:
alter table t_user
drop
foreign key FKCB63CCB61AEE691B
drop table if exists t_group
drop table if exists t_user
create table t_group (
id integer not null auto_increment,
name varchar(255),
primary key (id)
)
create table t_user (
id integer not null auto_increment,
name varchar(255),
group_id integer,
primary key (id)
)
alter table t_user
add index FKCB63CCB61AEE691B (group_id),
add constraint FKCB63CCB61AEE691B
foreign key (group_id)
references t_group (id)
schema export complete
结果在User表里的group_id属性上加了指向group的id的外键。(如果group_id存的数不是属于group表中数据的任何一个id,那么就不会被保存而报错,这就是外键的精髓)
转载请注明出处:http://blog.csdn.net/acmman