Hibernate_映射_关联关系_多对多映射2

package cn.itcast.g_hbm_manyToMany;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.Test;

/**
 * 应用程序操作类
 * 
 * @author 风清杨
 * @version V3.0
 * 
 */
public class App {
  private static SessionFactory sessionFactory = new Configuration()//
      .configure()//
      .addClass(Student.class)// 添加Hibernate实体类(加载对应的映射文件)
      .addClass(Teacher.class)// 添加Hibernate实体类(加载对应的映射文件)
      .buildSessionFactory();

  // 保存,有关联关系
  @Test
  public void testSave() throws Exception {
    Session session = sessionFactory.openSession();
    Transaction tx = null;
    try {
      tx = session.beginTransaction();
      // ------------------------------------

      // 构建老师对象
      Teacher teachers1 = new Teacher();
      teachers1.setName("张老师");
      Teacher teachers2 = new Teacher();
      teachers2.setName("赵老师");

      // 构建学生对象
      Student students1 = new Student();
      students1.setName("王小明");
      Student students2 = new Student();
      students2.setName("李冰冰");

      // 关联起来
      students1.getTeachers().add(teachers1);
      students1.getTeachers().add(teachers2);
      students2.getTeachers().add(teachers2);

      teachers1.getStudents().add(students1);
      teachers2.getStudents().add(students1);
      teachers2.getStudents().add(students2);

      // 保存
      session.save(students1);
      session.save(students2);
      session.save(teachers1);
      session.save(teachers2);
      // ------------------------------------
      tx.commit();
    } catch (RuntimeException e) {
      tx.rollback();
      throw e;
    } finally {
      session.close();
    }
  }

  // 获取,可以获取到关联的对方
  @Test
  public void testGet() throws Exception {
    Session session = sessionFactory.openSession();
    Transaction tx = null;
    try {
      tx = session.beginTransaction();
      // ------------------------------------

      // 获取一方数据,并显示另一方信息
      Teacher teacher = (Teacher) session.get(Teacher.class, 2L);
      System.out.println(teacher);
      System.out.println(teacher.getStudents());

      // ------------------------------------
      tx.commit();
    } catch (RuntimeException e) {
      tx.rollback();
      throw e;
    } finally {
      session.close();
    }
  }

  // 解除关联关系
  @Test
  public void testRemoveRelation() throws Exception {
    Session session = sessionFactory.openSession();
    Transaction tx = null;
    try {
      tx = session.beginTransaction();
      // ------------------------------------
      // 如果inverse=false就可以解除,如果为true就不可以解除
      Teacher teacher = (Teacher) session.get(Teacher.class, 2L);
      teacher.getStudents().clear();

      // ------------------------------------
      tx.commit();
    } catch (RuntimeException e) {
      tx.rollback();
      throw e;
    } finally {
      session.close();
    }
  }

  // 删除对象,对关联对象的影响
  @Test
  public void testDelete() throws Exception {
    Session session = sessionFactory.openSession();
    Transaction tx = null;
    try {
      tx = session.beginTransaction();
      // ------------------------------------
      // 删除部门方(一方)
      // a,如果没有关联的对方：
      // b,如果有关联的对方且inverse=false,由于可以维护关联关系,它就会先删除关联关系,再删除自已。
      // c,如果有关联的对方且inverse=true,由于不能维护关联关系,所以会直接执行删除自已,就会有异常。
      Teacher teacher = (Teacher) session.get(Teacher.class, 6L);
      session.delete(teacher);
      
      // ------------------------------------
      tx.commit();
    } catch (RuntimeException e) {
      tx.rollback();
      throw e;
    } finally {
      session.close();
    }
  }
}