双向多对多关联映射原理:
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假设,一个员工可能有多个角色,一个角色可能有多个员工,从员工或角色的角度看,这就是多对多的关系,不管从哪一个角度看,都是多对多的联系。多对多关联映射关系一般采用中间表的形式来实现,即新增一种包含关联双方主键的表。实现多对多关联关系,在数据库底层通过添加中间表指定关联关系,而在hibernate框架在双方的实体中添加一个保存对方的集合,在双方的映射文件中使用
如下图所示:
(1)XML版
Role类:
package Hibernate_demo1.Demo15.Entity; import java.util.Set; public class Role { private String id; private String rame; private Setusers; public String getId() { return id; } public void setId(String id) { this.id = id; } public String getRame() { return rame; } public void setRame(String rame) { this.rame = rame; } public Set getUsers() { return users; } public void setUsers(Set users) { this.users = users; } }
User类:
package Hibernate_demo1.Demo15.Entity; import java.util.Set; public class User { private String id; private String uname; private Setroles; public String getId() { return id; } public void setId(String id) { this.id = id; } public String getUname() { return uname; } public void setUname(String uname) { this.uname = uname; } public Set getRoles() { return roles; } public void setRoles(Set roles) { this.roles = roles; } }
Role.hbm.xml映射类:
<?xml version="1.0"?>
User.hbm.xml映射类:
<?xml version="1.0"?>
测试类:
package Hibernate_demo1.Demo15; import java.util.HashSet; import java.util.Set; import org.hibernate.Session; import Hibernate_demo1.Demo15.Entity.Role; import Hibernate_demo1.Demo15.Entity.User; import Hibernate_demo1.Demo15.Util.HibernateUtils; public class App { public static void main( String[] args ) { Session session = null; try{ session = HibernateUtils.getSession(); session.beginTransaction(); Role r1 = new Role(); r1.setRame("数据录入人员"); session.save(r1); Role r2 = new Role(); r2.setRame("商务主管"); session.save(r2); Role r3 = new Role(); r3.setRame("商务经理"); session.save(r3); Role r4 = new Role(); r4.setRame("项目会计"); session.save(r4); User u1 = new User(); u1.setUname("张三"); Setu1Roles = new HashSet (); u1Roles.add(r1); u1Roles.add(r2); u1.setRoles(u1Roles); session.save(u1); User u2 = new User(); u2.setUname("李四"); Set u2Roles = new HashSet (); u2Roles.add(r1); u2Roles.add(r2); u2Roles.add(r3); u2.setRoles(u2Roles); session.save(u2); User u3 = new User(); u3.setUname("王五"); Set u3Roles = new HashSet (); u3Roles.add(r3); u3Roles.add(r4); u3.setRoles(u3Roles); session.save(u3); session.getTransaction().commit(); }catch(Exception e){ e.printStackTrace(); session.getTransaction().rollback(); }finally{ HibernateUtils.closeSession(session); } } }
执行结果:
Hibernate: insert into role (rname, id) values (?, ?) Hibernate: insert into role (rname, id) values (?, ?) Hibernate: insert into role (rname, id) values (?, ?) Hibernate: insert into role (rname, id) values (?, ?) Hibernate: insert into user (uname, id) values (?, ?) Hibernate: insert into user (uname, id) values (?, ?) Hibernate: insert into user (uname, id) values (?, ?) Hibernate: insert into user_role (userid, roleid) values (?, ?) Hibernate: insert into user_role (userid, roleid) values (?, ?) Hibernate: insert into user_role (userid, roleid) values (?, ?) Hibernate: insert into user_role (userid, roleid) values (?, ?) Hibernate: insert into user_role (userid, roleid) values (?, ?) Hibernate: insert into user_role (userid, roleid) values (?, ?) Hibernate: insert into user_role (userid, roleid) values (?, ?)
数据库内容为:
user表:
role表:
user_role表:
(2)注解版
Role类:
package Hibernate_demo1.Demo16.Entity; import java.util.HashSet; import java.util.Set; import javax.persistence.CascadeType; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.ManyToMany; import javax.persistence.Table; import org.hibernate.annotations.GenericGenerator; @Entity @Table(name="role") public class Role { @Id @GenericGenerator(name="uuidGenerator", strategy="uuid") @GeneratedValue(generator="uuidGenerator") private String id; @Column(name="rname") private String rame; @ManyToMany(cascade=CascadeType.REFRESH,mappedBy="roles") private Setusers=new HashSet (); public String getId() { return id; } public void setId(String id) { this.id = id; } public String getRame() { return rame; } public void setRame(String rame) { this.rame = rame; } public Set getUsers() { return users; } public void setUsers(Set users) { this.users = users; } }
User类:
package Hibernate_demo1.Demo16.Entity; import java.util.HashSet; import java.util.Set; import javax.persistence.CascadeType; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.JoinTable; import javax.persistence.ManyToMany; import javax.persistence.Table; import javax.persistence.JoinColumn; import org.hibernate.annotations.GenericGenerator; @Entity @Table(name="user") public class User { @Id @GenericGenerator(name="uuidGenerator", strategy="uuid") @GeneratedValue(generator="uuidGenerator") private String id; @Column(name="uname") private String uname; /* * @ManyToMany表示多对多关联,对于这种关联极少数情况会使用级联删除,我这里设置的是级联刷新; * 因为有中间表的存在这里使用@JoinTable来设置关联表后面的name配置的是关联表的名称 * inverseJoinColumn配置的是关系被维护一方主键对应的中间表字段 * joinColumn配置的是关系维护方主键对应的中间表字段。 */ @ManyToMany(cascade=CascadeType.REFRESH) @JoinTable(name="user_role",inverseJoinColumns=@JoinColumn(name="roleid"),joinColumns=@JoinColumn(name="userid")) private Setroles=new HashSet (); public String getId() { return id; } public void setId(String id) { this.id = id; } public String getUname() { return uname; } public void setUname(String uname) { this.uname = uname; } public Set getRoles() { return roles; } public void setRoles(Set roles) { this.roles = roles; } }
测试类:
package Hibernate_demo1.Demo16; import java.util.HashSet; import java.util.Set; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import org.hibernate.cfg.Configuration; import Hibernate_demo1.Demo16.Entity.Role; import Hibernate_demo1.Demo16.Entity.User; public class Test { public static void main(String[] args) { SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory(); Session session = sessionFactory.getCurrentSession(); Transaction tx = session.beginTransaction(); //创建两个用户 User us1=new User(); us1.setUname("小明"); User us2=new User(); us2.setUname("小黑"); //创建用户集合 Setsu=new HashSet (); su.add(us1); su.add(us2); //创建两个角色 Role ro1=new Role(); ro1.setRame("程序员"); ro1.setUsers(su); Role ro2=new Role(); ro2.setRame("技术经理"); ro2.setUsers(su); //创建角色集合 Set sr=new HashSet (); sr.add(ro1); sr.add(ro2); //往用户添加角色集合 us1.setRoles(sr); us2.setRoles(sr); //保存用户和角色 session.save(us1); session.save(us2); session.save(ro1); session.save(ro2); tx.commit(); session.close(); } }
执行结果如下:
Hibernate: insert into user (uname, id) values (?, ?) Hibernate: insert into user (uname, id) values (?, ?) Hibernate: insert into role (rname, id) values (?, ?) Hibernate: insert into role (rname, id) values (?, ?) Hibernate: insert into user_role (userid, roleid) values (?, ?) Hibernate: insert into user_role (userid, roleid) values (?, ?) Hibernate: insert into user_role (userid, roleid) values (?, ?) Hibernate: insert into user_role (userid, roleid) values (?, ?)
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