详解hibernate双向多对多关联映射XML与注解版

详解hibernate双向多对多关联映射XML与注解版

双向多对多关联映射原理:

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元素和元素进行关联关系的配置。

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 Set users;

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 Set roles;

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:

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

User.hbm.xml映射类:

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

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 = newhttp:// 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");

Set u1Roles = 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 Set users=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 Set roles=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.SessioNBfNjFYn;

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

Set su=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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