hibernate单向多对多映射(many-to-many)XML与注解版

最新推荐文章于 2020-10-17 17:40:58 发布

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最新推荐文章于 2020-10-17 17:40:58 发布

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分类专栏： Hibernate

本文链接：https://blog.youkuaiyun.com/u011781521/article/details/71172874

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多对多关联映射需要新增加一张表才完成基本映射,他的实例场景如下:

用户与他的角色(一个用户拥有多个角色，一个角色还可以属于多个用户)

多对多关联映射,需要一个中间表,两个表中的主键放到第三张做一个关联,用第三张表来解决可能会造成数据冗余的问题,多对多的关联映射,在实体类中,跟一对多一样,也是用集合来表示的。

单向关联映射则是只能由A端去操作B端，B端不能操作A端的数据。而双向关联映射则是A，B两端都可以操作另一端的数据。

(1)XML版

SQL文件为:

CREATE TABLE `user` (
  `id` varchar(255) NOT NULL,
  `uname` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `role` (
  `id` varchar(255) NOT NULL,
  `rname` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `user_role` (
  `userid` varchar(255) DEFAULT NULL,
  `roleid` varchar(255) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Role实体类：

package Hibernate_demo1.Demo9.Entity;

import java.util.Set;

public class Role {
	
	private String id;
	private String rname;

	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getRname() {
		return rname;
	}
	public void setRname(String rname) {
		this.rname = rname;
	}
	
	

}

User实体类:

package Hibernate_demo1.Demo9.Entity;

import java.util.Set;

public class User {

	private String id;
	private String uname;
	private Set<Role> roles;  //角色集合,一个用户可以有多个角色
	
	public String getUname() {
		return uname;
	}
	public void setUname(String uname) {
		this.uname = uname;
	}
	public Set<Role> getRoles() {
		return roles;
	}
	public void setRoles(Set<Role> roles) {
		this.roles = roles;
	}
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return uname;
	}
	public void setName(String name) {
		this.uname = name;
	}
}

Role.hbm.xml映射文件:

<?xml version="1.0"?>  
<!DOCTYPE hibernate-mapping PUBLIC   
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">  
<hibernate-mapping>  
    <class name="Hibernate_demo1.Demo9.Entity.Role" table="role">  
        <id name="id" type="java.lang.String"> 
            <column name="id"/>
            <generator class="uuid">  
            </generator>  
        </id>  
        <property name="rname" column="rname"/>  
    </class>  
</hibernate-mapping>

User.hbm.xml 映射文件:

<?xml version="1.0"?>  
<!DOCTYPE hibernate-mapping PUBLIC   
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">  
<hibernate-mapping>  
    <class name="Hibernate_demo1.Demo9.Entity.User" table="user">  
        <id name="id">  
            <generator class="uuid">  
            </generator>  
        </id>  
        
        <property name="uname" column="uname"/>
     <!--
                    使用<set>标签映射集合(set)，标签中的name值为对象属性名(集合roles)
                    而使用table属性是用于生成第三方表名称，例：table="user_role"
                    但是第三方面中的字段是自动加入的，作为外键分别指向其它表。  
                     所以用<key>标签设置，例：<key column="userid"/>
                     意思是：在第三方表(user_role)中加入一个外键并且指向当前的映射实体类所对应的表(user)
                     使用<many-to-many>来指定此映射集合所对象的类(实例类)
                     并且使用column属性加入一个外键指向Role实体类所对应的表(role) 
      -->  
        <set name="roles" table="user_role">  
            <key column="userid"/>  
            <many-to-many class="Hibernate_demo1.Demo9.Entity.Role" column="roleid"/>  
        </set>  
    </class>  
</hibernate-mapping>

测试类如下:

package Hibernate_demo1.Demo9;

import java.util.HashSet;
import java.util.Set;

import org.hibernate.Session;

import Hibernate_demo1.Demo9.Entity.Role;
import Hibernate_demo1.Demo9.Entity.User;
import Hibernate_demo1.Demo9.Util.HibernateUtils;

public class App 
{
    public static void main( String[] args )
    {
    	Session session = null;
    	try{  
    		  
    	    session = HibernateUtils.getSession();
    	    session.beginTransaction();  
    	      
    	    //创建三个角色
    	    Role ro1=new Role();
    	    ro1.setRname("程序员");
    	    //保存角色
    	    session.save(ro1);
    	    
    	    Role ro2=new Role();
    	    ro2.setRname("产品经理");
    	    //保存角色
    	    session.save(ro2);
    	    
    	    
    	    Role ro3=new Role();
    	    ro3.setRname("CEO");
    	    //保存角色
    	    session.save(ro3);
    	    
    	    
    	    //创建两个用户
    	    User use1=new User();
    	    use1.setName("小明");
    	    
    	    User use2=new User();
    	    use2.setName("小黑");
    	    
    	    
    	    Set<Role> su=new HashSet();
    	    su.add(ro1);
    	    su.add(ro2);
    	    //给小明设置角色为(程序员,产品经理)
    	    use1.setRoles(su);
    	    
    	    Set<Role> su1=new HashSet();
    	    su1.add(ro3);
    	    
    	    //给小黑设置角色为(CEO)
    	    use2.setRoles(su1);
    	    
    	    session.save(use1);
    	    session.save(use2);
    	    
    	    session.getTransaction().commit();  
    	}catch(Exception e){  
    	    e.printStackTrace();  
    	    session.getTransaction().rollback();  
    	}finally{  
    	    HibernateUtils.closeSession(session);  
    	}
    }
}

执行结果如下:

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_role
        (userid, roleid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        user_role
        (userid, roleid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        user_role
        (userid, roleid) 
    values
        (?, ?)

效果为:

Role表

User表

user_role表

示例:http://download.youkuaiyun.com/detail/u011781521/9834640

(2)注解版

Role类

package Hibernate_demo1.Demo10.Entity;

import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
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 rname;

	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getRname() {
		return rname;
	}
	public void setRname(String rname) {
		this.rname = rname;
	}
}

User类

package Hibernate_demo1.Demo10.Entity;

import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.JoinColumn;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.OrderBy;
import javax.persistence.Table;


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(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    @JoinTable(name = "user_role", joinColumns = {@JoinColumn(name ="userid" )}, inverseJoinColumns = { @JoinColumn(name = "roleid") })
	private Set<Role> roles;  //角色集合,一个用户可以有多个角色
	
	public String getUname() {
		return uname;
	}
	public void setUname(String uname) {
		this.uname = uname;
	}
	public Set<Role> getRoles() {
		return roles;
	}
	public void setRoles(Set<Role> roles) {
		this.roles = roles;
	}
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return uname;
	}
	public void setName(String name) {
		this.uname = name;
	}
	
	
}

测试类:

package Hibernate_demo1.Demo10;

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.Demo10.Entity.Role;
import Hibernate_demo1.Demo10.Entity.User;

/**
 * Hello world!
 *
 */
public class App 
{
    public static void main( String[] args )
    {
    	SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();  
    	Session session = sessionFactory.getCurrentSession();  
    	Transaction tx = session.beginTransaction();  
        

    	//创建三个角色
	    Role ro1=new Role();
	    ro1.setRname("程序员");
	    //保存角色
	    session.save(ro1);
	    
	    Role ro2=new Role();
	    ro2.setRname("产品经理");
	    //保存角色
	    session.save(ro2);
	    
	    
	    Role ro3=new Role();
	    ro3.setRname("CEO");
	    //保存角色
	    session.save(ro3);
	    
	    
	    //创建两个用户
	    User use1=new User();
	    use1.setName("小明");
	    
	    User use2=new User();
	    use2.setName("小黑");
	    
	    
	    Set<Role> su=new HashSet();
	    su.add(ro1);
	    su.add(ro2);
	    //给小明设置角色为(程序员,产品经理)
	    use1.setRoles(su);
	    
	    Set<Role> su1=new HashSet();
	    su1.add(ro3);
	    
	    //给小黑设置角色为(CEO)
	    use2.setRoles(su1);
	    
	    session.save(use1);
	    session.save(use2);
    	
        tx.commit();
        session.close();
    }
}

执行结果如下:

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_role
        (userid, roleid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        user_role
        (userid, roleid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        user_role
        (userid, roleid) 
    values
        (?, ?)

示例:http://download.youkuaiyun.com/detail/u011781521/9834643