hibernate的list映射和map映射

墨蓝 2022-06-12 07:40 270阅读 0赞

这篇博客讲两个映射，一个是list，另一个是map

# list的映射 #

新建一个java项目

结构如下；

![Center][]

需要的jar包以及如何配置，请参见《[*Hibernate环境搭建和配置*][Hibernate]》

实体类Grade代码：

package com.robert.pojo;
    
    import java.util.ArrayList;
    import java.util.List;
    
    
    /**
     * 年级类
     */
    public class Grade {
    
    	private int id ;
    	private String name ;//年级名称
    	private List<Student> students = new ArrayList<Student>() ;
    	
    	public List<Student> getStudents() {
    		return students;
    	}
    	public void setStudents(List<Student> students) {
    		this.students = students;
    	}
    	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;
    	}
    	
    }

对应的配置文件Grade.hbm.xml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="Grade">
    		<id name="id">
    			<generator class="native"></generator>
    		</id>
    		<property name="name"></property>
    		
    		<list name="students">
    			
    			<key column="grade_id" not-null="true" />
    			
    			<list-index column="sort"></list-index>
    			
    			<one-to-many class="Student"/>
    		</list>
    	</class>
    </hibernate-mapping>

实体类Student代码：

package com.robert.pojo;
    
    /**
     * 学生类
     */
    public class Student {
    
    	private int id ;
    	private String name ;//姓名
    	private int age ;    //年龄
    	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 int getAge() {
    		return age;
    	}
    	public void setAge(int age) {
    		this.age = age;
    	}
    }

对应的配置文件Student.hbm.xml代码：

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/Grade.hbm.xml" />
    	<mapping resource="com/robert/pojo/Student.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代码：

package com.robert.test;
    
    import java.io.IOException;
    import java.sql.SQLException;
    import java.util.HashSet;
    import java.util.Iterator;
    import java.util.Set;
    
    import javax.sql.rowset.serial.SerialException;
    
    import org.hibernate.HibernateException;
    import org.hibernate.Session;
    import org.hibernate.Transaction;
    import org.hibernate.cfg.Configuration;
    import org.hibernate.tool.hbm2ddl.SchemaExport;
    import org.junit.Test;
    
    import com.robert.pojo.Grade;
    import com.robert.pojo.Student;
    import com.robert.util.HibernateUtil;
    
    public class HibernateTest {
    
    	/**
    	 * 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);
    	}
    
    	/**
    	 * 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();
    
    			Grade grade = new Grade();
    			grade.setName("基础") ;
    			session.save(grade);
    			
    			Student student = new Student() ;
    			student.setName("张三") ;
    			student.setAge(22) ;
    			
    			Student student2 = new Student() ;
    			student2.setName("李四") ;
    			student2.setAge(23) ;
    			
    			grade.getStudents().add(student) ;
    			grade.getStudents().add(student2);
    			//由于在Grade.hbm.xml中外键配置了not-null="true"，即不为空，
    			//所以先保存grade，再保存student；
    			//如果外键可为空，则先保存哪一个对象都可以；
    			session.save(grade);
    			session.save(student) ;
    			session.save(student2);
    			tx.commit();
    
    		} catch (HibernateException e) {
    			if (tx != null) {
    				tx.rollback();
    			}
    			e.printStackTrace();
    			throw e;
    		} finally {
    			HibernateUtil.closeSession();
    		}
    	}
    	
    	@Test
    	public void testGet() {
    		
    		Session session = null ;
    		Transaction tx = null ;
    		try {
    			session = HibernateUtil.getSession() ;
    			tx = session.beginTransaction() ;
    			//取数据
    			Grade grade = (Grade) session.get(Grade.class, 1) ;
    			System.out.println("grade_name:"+grade.getName());
    			Iterator<Student> it = grade.getStudents().iterator() ;
    			while (it.hasNext()) {
    				Student student = (Student) it.next();
    				System.out.println("student_name:"+student.getName());
    			}
    			tx.commit() ;
    		} catch (Exception e) {
    			tx.rollback();
    			e.printStackTrace();
    		}finally {
    			HibernateUtil.closeSession() ;
    		}
    		
    	}
    
    }

结果自己运行

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

# map映射 #

只有实体类Grade和Grade.hbm.xml配置文件和上面不同，其他的都相同

Grade代码：

package com.robert.pojo;
    
    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    
    
    /**
     * 年级类
     */
    public class Grade {
    
    	private int id ;
    	private String name ;//年级名称
    	private Map<String, Student> students = new HashMap<String, Student>() ;
    	
    	public Map<String, Student> getStudents() {
    		return students;
    	}
    	public void setStudents(Map<String, Student> students) {
    		this.students = students;
    	}
    	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;
    	}
    	
    }

Grade.hbm.xml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="Grade">
    		<id name="id">
    			<generator class="native"></generator>
    		</id>
    		<property name="name"></property>
    		<map name="students">
    			
    			<key column="grade_id" />
    			
    			<map-key type="string" column="name" />
    			<one-to-many class="Student"/>
    		</map>
    		
    	</class>
    </hibernate-mapping>

其他的自己运行测试就可以

[Center]: /images/20220612/4465a032a3c54ece9ccca5762d31e58c.png
[Hibernate]: http://blog.csdn.net/u011159417/article/details/75014665