hibernate的应用表之间的级联关系
1.联合主键映射
<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><!--指定映射文件所在的包路径--><hibernate-mapping package="tarena.domain"><class name="Person" table="person"><!--联合主键的配置--><composite-id name="key" type="string"><column name="first"></column></key-property><key-property name="last" type="string"><column name="last"></column></key-property></composite-id><property name="sex" type="string"><column name="sex"></column></property></class></hibernate-mapping>
pojo类实现，要有equals()和hashCode()方法
package tarena.domain;public class Person {private PersonKey key;private String sex;public PersonKey getKey() {return key;}public void setKey(PersonKey key) {this.key = key;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}@Overridepublic int hashCode() {final int PRIME = 31;int result = 1;result = PRIME * result + ((key == null) ? 0 : key.hashCode());result = PRIME * result + ((sex == null) ? 0 : sex.hashCode());return result;}@Overridepublic boolean equals(Object obj) {if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;final Person other = (Person) obj;if (key == null) {if (other.key != null)return false;} else if (!key.equals(other.key))return false;if (sex == null) {if (other.sex != null)return false;} else if (!sex.equals(other.sex))return false;return true;}}PsersonKey类
package tarena.domain;public class PersonKey implements java.io.Serializable{private String first;private String last;public PersonKey(){}public PersonKey(String first, String last) {super();this.first = first;this.last = last;}public String getFirst() {return first;}public void setFirst(String first) {this.first = first;}public String getLast() {return last;}public void setLast(String last) {this.last = last;}}2.外键，多对一/一对多
<!--Dept.hbm.xml--><hibernate-mapping package="tarena.domain"><class name="Dept" table="dept" lazy="true"><id name="id" type="integer"><column name="id"></column><!--id标识的生成策略，依赖于底层数据库的支持--><generator type="string"><column name="dname"></column></property><!--cascade="all"表示表示对象表之间的级联关系；one-to-many中级联的对象应由多(many)的一方来提供支持，many-to-many中可以是任意方--><set name="emps" cascade="all" inverse="true"><key column="dept_id"></key><one-to-many table="emp"><id name="id" type="integer"><column name="id"></column><generator type="string"><column name="ename"></column></property><!--class对应的级联表对象，fetch＝"join"表示表与表之间的抓取策略--><many-to-one name="dept" column="dept_id" fetch="join"></many-to-one></class></hibernate-mapping>
测试类，具体实现在后面依次添加
public class DeptDAOTest {DeptDAO deptDao;@Beforepublic void init(){deptDao = new DeptDAO();}//@Testpublic void testAdd1(){Dept dept = new Dept();dept.setDname("testing");deptDao.add(dept);}//@Test//测试级联添加public void testAdd2(){Dept dept = new Dept();dept.setDname("design");//添加新员工designer1Set<Emp> emps = new HashSet<Emp>();Emp emp1 = new Emp();emp1.setEname("designer1");emp1.setDept(dept);emps.add(emp1);//添加新员工designer2Emp emp2 = new Emp();emp2.setEname("designer2");emp2.setDept(dept);emps.add(emp2);//将员工集合emps指定给dept对象dept.setEmps(emps);deptDao.add(dept);}@Test//测试级联删除public void testDelete(){Dept dept = deptDao.findById(4);deptDao.delete(dept);}//@Testpublic void testFindById(){Dept dept = deptDao.findById(1);System.out.println(dept.getId()+":"+dept.getDname());Set<Emp> emps = dept.getEmps();for(Emp emp:emps){System.out.println(emp.getId()+":"+emp.getEname());}System.out.println("一共有"+emps.size()+"个员工");}}DeptDao代码
package tarena.dao;import org.hibernate.Session;import org.hibernate.Transaction;import tarena.domain.Dept;import tarena.util.HibernateUtil;public class DeptDAO {public Dept findById(int id){Session session = HibernateUtil.getSession();Dept dept = (Dept)session.load(Dept.class, id);return dept;}public void add(Dept dept){Session session = HibernateUtil.getSession();Transaction txt = session.beginTransaction();session.save(dept);txt.commit();HibernateUtil.closeSession();}public void delete(Dept dept){Session session = HibernateUtil.getSession();Transaction txt = session.beginTransaction();session.delete(dept);txt.commit();HibernateUtil.closeSession();}}3.理解延迟加载，区分load和get方法
//load方法启用延迟加载，返回的对象是一个代理对象//Dept dept = (Dept)session.load(Dept.class, 1);//get方法不启用延迟加载，立刻检索数据表，返回对象实例Dept dept = (Dept)session.get(Dept.class, 1);//HibernateUtil.closeSession();//如使用延迟加载，不要将session关闭，否则会影响后续取值操作//可以在业务操作都完成后，再将session关闭。//比如JavaWeb程序可以使用Filter控制session关闭//hibernate的默认配置是启用延迟，所以在使用get方法时，//可以Hibernate.initialize(obj)，来对对象进行初始化加载，不过要在session.colse()之前//或者可以把该对象的pojo类的映射文件的lazy="false"，就可以了。
首先，配置hibernate.cfg.xml不过一般用于测试使用，项目开发可以使用第三方的管理配置
<?xml version='1.0' encoding='UTF-8'?><!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"><!-- Generated by MyEclipse Hibernate Tools. --><hibernate-configuration><session-factory><property name="myeclipse.connection.profile">mysql</property><property name="connection.username">root</property><property name="connection.password">1234</property><property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property><!-- 是否使用数据库本地话方言 --><property name="dialect">org.hibernate.dialect.MySQLDialect</property><property name="connection.driver_class">com.mysql.jdbc.Driver</property><!-- 是否打印hql语句 --><property name="show_sql">true</property><!-- 对象的关系映射 --><mapping resource="tarena/mapping/Person.hbm.xml" /><mapping resource="tarena/mapping/Dept.hbm.xml" /><mapping resource="tarena/mapping/Emp.hbm.xml" /></session-factory></hibernate-configuration>
hibernateUtil的配置
package tarena.util;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;public class HibernateUtil {public static Configuration conf;public static SessionFactory sf;public static ThreadLocal<Session> sessionLocal = new ThreadLocal<Session>();static{conf = new Configuration();conf.configure();//默认加载src下面的hibernate.cfg.xml配置文件sf = conf.buildSessionFactory();}public static Session getSession() {Session session = sessionLocal.get();if(session == null){session = sf.openSession();sessionLocal.set(session);}return session;}public static void closeSession(){Session session = sessionLocal.get();sessionLocal.set(null);if(session != null){session.close();}}}pojo类Dept
package tarena.domain;import java.io.Serializable;import java.util.Set;public class Dept implements Serializable{private int id;private String dname;private Set<Emp> emps;public String getDname() {return dname;}public void setDname(String dname) {this.dname = dname;}public int getId() {return id;}public void setId(int id) {this.id = id;}public Set<Emp> getEmps() {return emps;}public void setEmps(Set<Emp> emps) {this.emps = emps;}}