Hibernate 一对多注解 实例

案例分析：班级clazz与学生student是一对多关系，反过来学生和班级是多对一关系。

hihernate一对多关联映射（双向Clazz<—–>Student）
一对多双向关联映射：
* 在”一”一端的集合上使用@OneToMany和mapperBy，在对方表中加入一个外键指向“一”一端
* 在多一端采用@ManyToOne和@JoinColumn

如果在”一“一端维护一对多关联关系，hibernate会发出多余的udpate语句，所以我们一般在多的一端来维护关联关系。

Student.java

package com.wonders.task.sample.bo;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;import javax.persistence.Table;import org.hibernate.annotations.GenericGenerator;@Entity @Table(name="Z_STUDENT") public class Student {    private String id;    private String name;    private Clazz clazz;    @Id    @GeneratedValue(generator="system-uuid")    @GenericGenerator(name="system-uuid", strategy = "uuid")    @Column(name = "ID")    public String getId() {        return id;    }    public void setId(String id) {        this.id = id;    }    @Column(name = "NAME", length = 500)    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    //在“多”的这方定义@ManytoOne,同时引入“一”那方的主键，也是“多”这方的外键。    @ManyToOne(cascade={CascadeType.ALL})             @JoinColumn(name="class_id")     //student类中对应外键的属性：classid     public Clazz getClazz() {        return clazz;    }    public void setClazz(Clazz clazz) {        this.clazz = clazz;    }}

Clazz.java

package com.wonders.task.sample.bo;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.OneToMany;import javax.persistence.Table;import org.hibernate.annotations.GenericGenerator;@Entity @Table(name="Z_CLASS") public class Clazz implements java.io.Serializable{    /**     * Clazz是关系被维护方，Student是关系维护方，要把class的值通过student的setClazz（）方法赋给student，最后session.save()保存的是student对象。     */    private static final long serialVersionUID = -6224738252966513441L;    private String id;    private String name;    private Set<Student> set;    @Id    @GeneratedValue(generator="system-uuid")    @GenericGenerator(name="system-uuid", strategy = "uuid")    @Column(name = "ID")    public String getId() {        return id;    }    public void setId(String id) {        this.id = id;    }    @Column(name = "NAME", length = 500)    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    //在“一”这方配置@OneToMany,同时配置mapperBy指向当前（“一”）这方，也就是被维护方    @OneToMany(cascade=CascadeType.ALL,mappedBy="clazz")        //@OneToMany(cascade=CascadeType.ALL,mappedBy="clazz",fetch=FetchType.EAGER) 关闭延迟加载。            public Set<Student> getSet() {        return set;    }    public void setSet(Set<Student> set) {        this.set = set;    }   }

Main.java

package com.wonders.task.sample.main;import java.util.HashSet;import java.util.Set;import javax.annotation.Resource;import org.hibernate.Hibernate;import org.hibernate.Session;import org.springframework.context.ApplicationContext;import org.springframework.context.annotation.Scope;import org.springframework.context.support.ClassPathXmlApplicationContext;import org.springframework.orm.hibernate3.HibernateTemplate;import org.springframework.stereotype.Service;import org.springframework.transaction.annotation.Propagation;import org.springframework.transaction.annotation.Transactional;import com.wonders.schedule.util.SpringBeanUtil;import com.wonders.task.sample.ITaskService;import com.wonders.task.sample.bo.Clazz;import com.wonders.task.sample.bo.Student;@Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class)/* 功能模块入口点，beanid即数据库配置中的name */@Service("testMain")@Scope("prototype")public class TestMain {    private HibernateTemplate hibernateTemplate;    public HibernateTemplate getHibernateTemplate() {        return hibernateTemplate;    }    //注入hibernateTemplate    @Resource(name="hibernateTemplate")    public void setHibernateTemplate(HibernateTemplate hibernateTemplate) {        this.hibernateTemplate = hibernateTemplate;    }    public void test(){        Session session = this.getHibernateTemplate().getSessionFactory().getCurrentSession();        Clazz c2 = (Clazz) session.get(Clazz.class, "8a81a97c4471c661014471c669360002");        //Clazz c2 = (Clazz) main.getHibernateTemplate().get(Clazz.class, "8a81a97c4471c661014471c669360002");        Hibernate.initialize(c2.getSet());        System.out.println("11111111111111111111111");        //session.close();        Set<Student> sss =  c2.getSet();        System.out.println("22222222222222222");        for(Student s: sss){            System.out.println(s.getName());        }    }    public static void main(String[] args){        ApplicationContext applicationContext = null;          String[] fileUrl = new String[]{"classpath*:applicationContext*.xml"};          applicationContext = new ClassPathXmlApplicationContext(fileUrl);          Student s1 = new Student();        Student s2 = new Student();        Clazz c1 = new Clazz();        c1.setName("1班");        s1.setName("z1");        s1.setClazz(c1);        s2.setName("z2");        s2.setClazz(c1);        Set<Student> set = new HashSet<Student>();        set.add(s1);set.add(s2);        c1.setSet(set);        TestMain main = (TestMain)SpringBeanUtil.getBean("testMain");        //main.getHibernateTemplate().save(c1);//      Session session = main.getHibernateTemplate().getSessionFactory().openSession();//      Clazz c2 = (Clazz) session.get(Clazz.class, "8a81a97c4471c661014471c669360002");//      //Clazz c2 = (Clazz) main.getHibernateTemplate().get(Clazz.class, "8a81a97c4471c661014471c669360002");//      Hibernate.initialize(c2.getSet());//      //      System.out.println("11111111111111111111111");//      session.close();//      Set<Student> sss =  c2.getSet();//      System.out.println("22222222222222222");//      for(Student s: sss){//          //          System.out.println(s.getName());//      }        main.test();        //main.getHibernateTemplate().delete(c2);    }}

级联保存：
方法一：自动维护两表关系，（clazz）mappedby 为被维护方，对应的student为维护方

Student s1 = new Student();        Student s2 = new Student();        Clazz c1 = new Clazz();        c1.setName("1班");        s1.setName("z1");        s1.setClazz(c1);        s2.setName("z2");        s2.setClazz(c1);        TestMain main = (TestMain)SpringBeanUtil.getBean("testMain");        main.getHibernateTemplate().save(s1);        main.getHibernateTemplate().save(s2);

方法2：手动维护，两方都需要set对应对方的变量

Student s1 = new Student();        Student s2 = new Student();        Clazz c1 = new Clazz();        c1.setName("1班");        s1.setName("z1");        s1.setClazz(c1);        s2.setName("z2");        s2.setClazz(c1);        Set<Student> set = new HashSet<Student>();          set.add(s1);set.add(s2);        c1.setSet(set);        TestMain main = (TestMain)SpringBeanUtil.getBean("testMain");        main.getHibernateTemplate().save(c1);