Hibernate多对多关联

缺乏、安全感 2022-05-24 09:10 212阅读 0赞

#### 【例】学生选课 ####

##### 第一步：创建数据表 #####

课程表

![20180524151104102][]

学生表

![20180524151111151][]

##### 第二步：创建实体类 #####

学生类

package com.dwx.entity;
    import java.util.Set;
    public class Student {
    	private int sid;
    	private String sname;
    	private Set<Course>courses;
    	public int getSid() {
    		return sid;
    	}
    	public void setSid(int sid) {
    		this.sid = sid;
    	}
    	public String getSname() {
    		return sname;
    	}
    	public void setSname(String sname) {
    		this.sname = sname;
    	}
    	public Set<Course> getCourses() {
    		return courses;
    	}
    	public void setCourses(Set<Course> courses) {
    		this.courses = courses;
    	}
    }

课程类

package com.dwx.entity;
    public class Course {
    	private int cid;
    	private String cname;
    	public int getCid() {
    		return cid;
    	}
    	public void setCid(int cid) {
    		this.cid = cid;
    	}
    	public String getCname() {
    		return cname;
    	}
    	public void setCname(String cname) {
    		this.cname = cname;
    	}
    }

##### 第三步：配置映射 #####

Student.hbm.xml

<?xml version="1.0" encoding="utf-8"?>
    <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    <hibernate-mapping>
        <class name="com.dwx.entity.Student" table="student" catalog="register">
            <id name="sid" >
                <column name="sid" />
                <generator class="increment" />
            </id>        
            <property name="sname"></property>
            <set name="courses" table="stu_course" cascade="save-update">
            	<key column="sid"></key>
            	<many-to-many column="cid" class="com.dwx.entity.Course"></many-to-many>
            </set>
        </class>
    </hibernate-mapping>

Course.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    <hibernate-mapping>
    	<class name="com.dwx.entity.Course" table="course">
    		<id name="cid">
    			<generator class="increment"></generator>
    		</id>
    		<property name="cname"></property>
    	</class>
    </hibernate-mapping>

##### 第四步：引入映射文件 #####

<?xml version='1.0' encoding='UTF-8'?>
    <!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="myeclipse.connection.profile">register</property>
    	<property name="dialect">
    		org.hibernate.dialect.MySQL5InnoDBDialect
    	</property>
    	<property name="connection.password">root</property>
    	<property name="connection.username">root</property>
    	<property name="connection.url">
    		jdbc:mysql://localhost:3306/register
    	</property>
    	<property name="connection.driver_class">
    		com.mysql.jdbc.Driver
    	</property>
    	<property name="show_sql">true</property>
    	<property name="hbm2ddl.auto">update</property>
    	<property name="javax.persistence.validation.mode">none</property>
    	<mapping resource="com/dwx/entity/Course.hbm.xml" />
    	<mapping resource="com/dwx/entity/Student.hbm.xml" />
    </session-factory>
    </hibernate-configuration>

##### 第五步：创建HibernateSessionFactory #####

package com.dwx.utils;
    
    import org.hibernate.HibernateException;
    import org.hibernate.Session;
    import org.hibernate.cfg.Configuration;
    import org.hibernate.service.ServiceRegistry;
    import org.hibernate.boot.MetadataSources;
    import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
    
    /**
     * Configures and provides access to Hibernate sessions, tied to the
     * current thread of execution.  Follows the Thread Local Session
     * pattern, see {@link http://hibernate.org/42.html }.
     */
    public class HibernateSessionFactory {
    
        /** 
         * Location of hibernate.cfg.xml file.
         * Location should be on the classpath as Hibernate uses  
         * #resourceAsStream style lookup for its configuration file. 
         * The default classpath location of the hibernate config file is 
         * in the default package. Use #setConfigFile() to update 
         * the location of the configuration file for the current session.   
         */
    	private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
        private static org.hibernate.SessionFactory sessionFactory;
    	
        private static Configuration configuration = new Configuration();
        private static ServiceRegistry serviceRegistry; 
    
    	static {
        	try {
    			configuration.configure();
    			serviceRegistry = new StandardServiceRegistryBuilder().configure().build();
    			try {
    				sessionFactory = new MetadataSources(serviceRegistry).buildMetadata().buildSessionFactory();
    			} catch (Exception e) {
    				StandardServiceRegistryBuilder.destroy(serviceRegistry);
    				e.printStackTrace();
    			}
    		} catch (Exception e) {
    			System.err.println("%%%% Error Creating SessionFactory %%%%");
    			e.printStackTrace();
    		}
        }
        private HibernateSessionFactory() {
        }
    	
    	/**
         * Returns the ThreadLocal Session instance.  Lazy initialize
         * the <code>SessionFactory</code> if needed.
         *
         *  @return Session
         *  @throws HibernateException
         */
        public static Session getSession() throws HibernateException {
            Session session = (Session) threadLocal.get();
    
    		if (session == null || !session.isOpen()) {
    			if (sessionFactory == null) {
    				rebuildSessionFactory();
    			}
    			session = (sessionFactory != null) ? sessionFactory.openSession()
    					: null;
    			threadLocal.set(session);
    		}
    
            return session;
        }
    
    	/**
         *  Rebuild hibernate session factory
         *
         */
    	public static void rebuildSessionFactory() {
    		try {
    			configuration.configure();
    			serviceRegistry = new StandardServiceRegistryBuilder().configure().build();
    			try {
    				sessionFactory = new MetadataSources(serviceRegistry).buildMetadata().buildSessionFactory();
    			} catch (Exception e) {
    				StandardServiceRegistryBuilder.destroy(serviceRegistry);
    				e.printStackTrace();
    			}
    		} catch (Exception e) {
    			System.err.println("%%%% Error Creating SessionFactory %%%%");
    			e.printStackTrace();
    		}
    	}
    
    	/**
         *  Close the single hibernate session instance.
         *
         *  @throws HibernateException
         */
        public static void closeSession() throws HibernateException {
            Session session = (Session) threadLocal.get();
            threadLocal.set(null);
    
            if (session != null) {
                session.close();
            }
        }
    
    	/**
         *  return session factory
         *
         */
    	public static org.hibernate.SessionFactory getSessionFactory() {
    		return sessionFactory;
    	}
    	/**
         *  return hibernate configuration
         *
         */
    	public static Configuration getConfiguration() {
    		return configuration;
    	}
    
    }

##### 第六步：创建测试类 #####

package com.dwx.entity;
    import java.util.HashSet;
    import java.util.Set;
    import org.hibernate.Session;
    import org.hibernate.Transaction;
    import com.dwx.utils.HibernateSessionFactory;
    public class StuCourse {
    	public static void main(String[] args) {
    		Session session=null;
    		Transaction tx=null;
    		try{
    			session=HibernateSessionFactory.getSession();
    			tx=session.beginTransaction();
    			//创建三门课程
    			Course c1=new Course();
    			c1.setCname("数据结构");
    			Course c2=new Course();
    			c2.setCname("Java从入门到精通");
    			Course c3=new Course();
    			c3.setCname("计算机原理");
    			
    			Set<Course>course1=new HashSet<Course>();
    			course1.add(c1);
    			course1.add(c2);
    			Set<Course>course2=new HashSet<Course>();
    			course2.add(c1);
    			course2.add(c3);
    			//创建两个学生
    			Student stu1=new Student();
    			stu1.setSname("马向林");
    			stu1.setCourses(course1);
    			Student stu2=new Student();
    			stu2.setSname("白雪");
    			stu2.setCourses(course2);
    			
    			session.save(stu1);
    			session.save(stu2);
    			tx.commit();
    		}catch(Exception e){
    			e.printStackTrace();
    		}finally{
    			HibernateSessionFactory.closeSession();
    		}
    	}
    }

效果：

![20180524151735495][]

![20180524151745371][]

![20180524151753787][]

[20180524151104102]: /images/20220524/f9162c1a909444df888725ce8d503031.png
[20180524151111151]: /images/20220524/eaf41b0aea5d4565a2259c26a7bff1f4.png
[20180524151735495]: /images/20220524/c693a5dd487a4b4badc4f66d715c6b34.png
[20180524151745371]: /images/20220524/c5c42da1dc6b4192a407c4fdba583f75.png
[20180524151753787]: /images/20220524/d675ac5f2b5f46e99a358011020299ea.png