HIbernate的多对多关系-----单向和多向

谁践踏了优雅 2022-06-12 06:56 192阅读 0赞

当数据库表结构是多对多关系时，对应的实体类和相应的配置文件也需要是多对多的，多对多关系分为单向和多向，

# 一、单向 #

新建java项目，结构为：

![Center][]

需要的jar包及如何从hibernate官网获取jar包，请参见《[*Hibernate环境搭建和配置*][Hibernate]》

实体类Function代码：

package com.robert.pojo;
    
    public class Function {
    
    	private int id ;
    	private String name ;
    	private String code ;
    	private String url ;
    	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;
    	}
    	public String getCode() {
    		return code;
    	}
    	public void setCode(String code) {
    		this.code = code;
    	}
    	public String getUrl() {
    		return url;
    	}
    	public void setUrl(String url) {
    		this.url = url;
    	}
    	
    }

Function.hbm.xml配置文件代码：

实体类Role代码：

package com.robert.pojo;
    
    import java.util.HashSet;
    import java.util.Set;
    
    public class Role {
    
    	private int id ;
    	private String name ;
    	private Set<Function> functions = new HashSet<Function>() ;
    	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;
    	}
    	public Set<Function> getFunctions() {
    		return functions;
    	}
    	public void setFunctions(Set<Function> functions) {
    		this.functions = functions;
    	}
    	
    	
    }

Role.hbm.xml配置文件代码:

<?xml version="1.0"?>
    <!DOCTYPE hibernate-mapping PUBLIC 
    	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    	"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    
    <hibernate-mapping package="com.robert.pojo">
    	<class name="Role">
    		<id name="id">
    			<generator class="native"></generator>
    		</id>
    		<property name="name"></property>
    		
    		<set name="functions" table="Role_Function" cascade="all">
    			<key column="role_id" />
    			<many-to-many column="function_id" class="Function" />
    		</set>
    	</class>
    </hibernate-mapping>

关于连接表的配置信息，在文档中也是有的，如图：

![Center 1][]

hibernate.cfg.xml代码：

<!DOCTYPE hibernate-configuration PUBLIC
    	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    	"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
    
    <hibernate-configuration>
    <session-factory>
    	
    	<property name="connection.driver_class">
    		com.mysql.jdbc.Driver
    	</property>
    	<property name="connection.url">jdbc:mysql:///hibernate4</property>
    	<property name="connection.username">root</property>
    	<property name="connection.password">root</property>
    	
    	<property name="hibernate.dialect">
    		org.hibernate.dialect.MySQL5Dialect
    	</property>
    	
    	<property name="show_sql">true</property>
    	
    	<property name="format_sql">true</property>
    	
    	<property name="hbm2ddl.auto">update</property>
    
    	
    	<mapping resource="com/robert/pojo/Function.hbm.xml" />
    	<mapping resource="com/robert/pojo/Role.hbm.xml" />
    
    </session-factory>
    </hibernate-configuration>

HIbernateUtil代码：

package com.robert.util;
    
    import org.hibernate.Session;
    import org.hibernate.SessionFactory;
    import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
    import org.hibernate.cfg.Configuration;
    
    /**
     * hibernate工具类
     */
    public class HibernateUtil {
    
    	private static Configuration cfg = null;
    	private static SessionFactory factory = null;
    	private static Session session = null ;
    	
    	static {
    		init();
    	}
    
    	/**
    	 * 初始化获得Configuration和SessionFacroty对象
    	 */
    	public static void init() {
    		cfg = new Configuration().configure();
    		factory = cfg.buildSessionFactory(new StandardServiceRegistryBuilder()
    				.applySettings(cfg.getProperties()).build());
    	}
    
    	/**
    	 * 获得Session对象
    	 * @return
    	 */
    	public static Session getSession() {
    		if (factory != null){
    			return session = factory.openSession();
    		}
    		
    
    		init();
    		return session = factory.openSession();
    	}
    	
    	/**
    	 * 关闭Session
    	 */
    	public static void closeSession() {
    		if(session!=null && session.isOpen())
    			session.close();
    	}
    
    }

HibernateTest中testCreateDB代码：

/**
    	 * 根据*.hbm.xml文件对应的生成数据库表
    	 */
    	@Test
    	public void testCreateDB() {
    		Configuration cfg = new Configuration().configure();
    		SchemaExport se = new SchemaExport(cfg);
    		// 第一个参数：是否生成ddl脚本
    		// 第二个参数：是否执行到数据库中
    		se.create(true, true);
    	}

运行testCreateDB，创建数据库表

控制台打印的sql语句：

alter table Role_Function 
            drop 
            foreign key FK_ffk1sq7hplj96dsmj3vsxlfwx
    
        alter table Role_Function 
            drop 
            foreign key FK_eogfmuh5hen05bqkg8sufs2pa
    
        drop table if exists Function
    
        drop table if exists Role
    
        drop table if exists Role_Function
    
        create table Function (
            id integer not null auto_increment,
            name varchar(255),
            code varchar(255),
            url varchar(255),
            primary key (id)
        )
    
        create table Role (
            id integer not null auto_increment,
            name varchar(255),
            primary key (id)
        )
    
        create table Role_Function (
            role_id integer not null,
            function_id integer not null,
            primary key (role_id, function_id)
        )
    
        alter table Role_Function 
            add constraint FK_ffk1sq7hplj96dsmj3vsxlfwx 
            foreign key (function_id) 
            references Function (id)
    
        alter table Role_Function 
            add constraint FK_eogfmuh5hen05bqkg8sufs2pa 
            foreign key (role_id) 
            references Role (id)

生成的数据库表如图：  
![Center 2][]

testSave()方法代码如下：

/**
    	 * 保存数据
    	 * 
    	 * @throws HibernateException
    	 * @throws SerialException
    	 * @throws SQLException
    	 * @throws IOException
    	 */
    	@Test
    	public void testSave() throws HibernateException, SerialException,
    			SQLException, IOException {
    		Session session = null;
    		Transaction tx = null;
    		try {
    			session = HibernateUtil.getSession();
    			tx = session.beginTransaction();
    
    			Function function1 = new Function("用户管理", "user_mag", "userAction") ;
    			Function function2 = new Function("角色管理", "role_mag", "roleAction") ;
    			Function function3 = new Function("系统管理", "sys_mag", "sysAction") ;
    			Function function4 = new Function("权限管理", "prev_mag", "prevAction") ;
    			
    			Role role = new Role() ;
    			role.setName("admin") ;
    			role.getFunctions().add(function1) ;
    			role.getFunctions().add(function2) ;
    			role.getFunctions().add(function3) ;
    			role.getFunctions().add(function4) ;
    			
    
    			Role role2 = new Role() ;
    			role2.setName("vip") ;
    			role2.getFunctions().add(function1) ;
    			role2.getFunctions().add(function2) ;
    			
    			session.save(role) ;
    			session.save(role2) ;
    
    			tx.commit();
    
    		} catch (HibernateException e) {
    			if (tx != null) {
    				tx.rollback();
    			}
    			e.printStackTrace();
    			throw e;
    		} finally {
    			HibernateUtil.closeSession();
    		}
    	}

使用Junit4运行，控制台打印sql语句如下：

Hibernate: 
        insert 
        into
            Role
            (name) 
        values
            (?)
    Hibernate: 
        insert 
        into
            Function
            (name, code, url) 
        values
            (?, ?, ?)
    Hibernate: 
        insert 
        into
            Function
            (name, code, url) 
        values
            (?, ?, ?)
    Hibernate: 
        insert 
        into
            Function
            (name, code, url) 
        values
            (?, ?, ?)
    Hibernate: 
        insert 
        into
            Function
            (name, code, url) 
        values
            (?, ?, ?)
    Hibernate: 
        insert 
        into
            Role
            (name) 
        values
            (?)
    Hibernate: 
        insert 
        into
            Role_Function
            (role_id, function_id) 
        values
            (?, ?)
    Hibernate: 
        insert 
        into
            Role_Function
            (role_id, function_id) 
        values
            (?, ?)
    Hibernate: 
        insert 
        into
            Role_Function
            (role_id, function_id) 
        values
            (?, ?)
    Hibernate: 
        insert 
        into
            Role_Function
            (role_id, function_id) 
        values
            (?, ?)
    Hibernate: 
        insert 
        into
            Role_Function
            (role_id, function_id) 
        values
            (?, ?)
    Hibernate: 
        insert 
        into
            Role_Function
            (role_id, function_id) 
        values
            (?, ?)

数据库表中的数据如：

![Center 3][]

==============================================================

# 二、多向 #

项目结构以及大部分代码都和上面单向的项目一样，下面只列举出不同的代码

Role实体类新增加了关联Function代码，如下：

package com.robert.pojo;
    
    import java.util.HashSet;
    import java.util.Set;
    
    public class Role {
    
    	private int id ;
    	private String name ;
    	private Set<Function> functions = new HashSet<Function>() ;//关联function
    	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;
    	}
    	public Set<Function> getFunctions() {
    		return functions;
    	}
    	public void setFunctions(Set<Function> functions) {
    		this.functions = functions;
    	}
    	
    	
    }

Role.hbm.xml代码增加了function的多对多的配置，代码如下：

<?xml version="1.0"?>
    <!DOCTYPE hibernate-mapping PUBLIC 
    	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    	"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    
    <hibernate-mapping package="com.robert.pojo">
    	<class name="Role">
    		<id name="id">
    			<generator class="native"></generator>
    		</id>
    		<property name="name"></property>
    		
    		<set name="functions" table="Role_Function" cascade="save-update">
    			<key column="role_id" />
    			<many-to-many column="function_id" class="Function" />
    		</set>
    	</class>
    </hibernate-mapping>

注意：cascade必须是save-update才可以，

all时会报错，delete时会将function中的数据也删除。

运行testCreateDB，生成数据库表

运行testSave()方法，保存数据

都和上线的单向一样

写一个删除方法，删除role对象时，查看关联的表中对应的数据，是否会被删除，

testDelete（）方法如下：

/**
    	 * 删除方法
    	 * @throws HibernateException
    	 * @throws SerialException
    	 * @throws SQLException
    	 * @throws IOException
    	 */
    	@Test
    	public void testDelete() throws HibernateException, SerialException,
    			SQLException, IOException {
    		Session session = null;
    		Transaction tx = null;
    		try {
    			session = HibernateUtil.getSession();
    			tx = session.beginTransaction();
    
    			Role role = (Role) session.get(Role.class, 1) ;
    			System.out.println("--------------------------------------");
    			session.delete(role) ;
    			
    			tx.commit();
    
    		} catch (HibernateException e) {
    			if (tx != null) {
    				tx.rollback();
    			}
    			e.printStackTrace();
    			throw e;
    		} finally {
    			HibernateUtil.closeSession();
    		}
    
    	}

运行后，控制台打印的sql语句如下：

Hibernate: 
        select
            role0_.id as id1_1_0_,
            role0_.name as name2_1_0_ 
        from
            Role role0_ 
        where
            role0_.id=?
    --------------------------------------
    Hibernate: 
        delete 
        from
            Role_Function 
        where
            role_id=?
    Hibernate: 
        delete 
        from
            Role 
        where
            id=?

查看数据库表Role和role\_function中的相关数据已经被删除

[Center]: /images/20220612/588110e2ec1a46f284e51ebea49e701d.png
[Hibernate]: http://blog.csdn.net/u011159417/article/details/75014665
[Center 1]: /images/20220612/fd2139f7e7ef4f5a8c134c30c7726387.png
[Center 2]: /images/20220612/5e5586f7ece8407b818a381aea0e4ee1.png
[Center 3]: /images/20220612/83b9798e8cc5442db05cc5a2ffa110c9.png