Hiberante(七) ManyToMany_xml 单向和双向关联

ManyToMany(2种解决方案< 1.直接多对多，2.分解成连个oneToMany >) 

 

(1).第一种方式：

  实体类：

  Admin.java

 

public class Admin {
	private int id;
	private String name;
	private Set<Role> roles;
  省略get,set
}

   Role.java

 

public class Role {
	private int id;
	private String name;
	private Set<Admin> admins;
  省略get,set
}

  hbm文件

  Admin.hbm.xml

<hibernate-mapping package="org.zttc.itat.model">
	<class name="Admin" table="t_admin">
		<id name="id">
			<generator class="native" />
		</id>
		<property name="name" />
		<set name="roles" table="t_admin_role" lazy="extra">
			<key column="aid" />
			<many-to-many class="Role" column="rid" />
		</set>
	</class>
</hibernate-mapping>

 Role.hbm.xml

 

<hibernate-mapping package="org.zttc.itat.model">
	<class name="Role" table="t_role">
		<id name="id">
			<generator class="native" />
		</id>
		<property name="name" />
		<set name="admins" table="t_admin_role" lazy="extra">
			<key column="rid" />
			<many-to-many class="Admin" column="aid" />
		</set>
	</class>
</hibernate-mapping>

 

 测试方法：

/*
	 * 使用Many2Many不论在哪一方来维护关系都比较的麻烦，而且很多时候关联表中需要加入其他的属性
	 * 所以在开发中，经常使用两个一对多来替代多对多
	 */
	@Test
	public void testAdd01() {
		Session session = null;
		try {
			session = HibernateUtil.openSession();
			session.beginTransaction();
			Admin a1 = new Admin();
			a1.setName("张三");
			session.save(a1);
			Admin a2 = new Admin();
			a2.setName("李四");
			session.save(a2);
			Role r1= new Role();
			r1.setName("超级管理员");
			r1.add(a1);
			session.save(r1);
			Role r2 = new Role();
			r2.setName("财务管理人员");
			r2.add(a1);
			r2.add(a2);
			session.save(r2);
			
			session.getTransaction().commit();
		} catch (Exception e) {
			e.printStackTrace();
			if(session!=null) session.getTransaction().rollback();
		} finally {
			HibernateUtil.close(session);
		}
	}
	
	@Test
	public void testLoad01() {
		Session session = null;
		try {
			session = HibernateUtil.openSession();
			session.beginTransaction();
			Admin a = (Admin)session.load(Admin.class, 1);
			System.out.println(a.getName());
			for(Role r:a.getRoles()) {
				System.out.println(r.getName());
			}
			session.getTransaction().commit();
		} catch (Exception e) {
			e.printStackTrace();
			if(session!=null) session.getTransaction().rollback();
		} finally {
			HibernateUtil.close(session);
		}
	}

 

(2).第二种方式

   实体类：

 

public class Teacher {
	private int id;
	private String name;
	private Set<TeacherCourse> tcs;
  省略get,set
}

 

public class Course {
	private int id;
	private String name;
	private Set<TeacherCourse> tcs;
 省略get,set
}

 

public class TeacherCourse {
	private int id;
	private double ach;
	private Teacher teacher;
	private Course course;
 省略get,set
}

 

  hbm文件

 

<hibernate-mapping package="org.th.model">
    <class name="Teacher" table="t_teacher">
        <id name="id">
          	<generator class="native"/>
        </id>
        <property name="name"/>
        <set name="tcs" lazy="extra" inverse="true">
        	<key column="tid"/>
        	<one-to-many class="TeacherCourse"/>
        </set>
    </class>
</hibernate-mapping>

 

<hibernate-mapping package="org.th.model">
    <class name="Course" table="t_course">
        <id name="id">
          	<generator class="native"/>
        </id>
        <property name="name"/>
        <set name="tcs" lazy="extra" inverse="true">
        	<key column="cid"/>
        	<one-to-many class="TeacherCourse"/>
        </set>
    </class>
</hibernate-mapping>

    

<hibernate-mapping package="org.th.model">
    <class name="TeacherCourse" table="t_teacher_course">
        <id name="id">
          	<generator class="native"/>
        </id>
        <property name="ach"/>
        <many-to-one name="teacher" column="tid"/>
        <many-to-one name="course" column="cid"/>
    </class>
</hibernate-mapping>

 

   测试方法：

 

@Test
	public void testAdd01() {
		Session session = null;
		try {
			session = HibernateUtil.openSession();
			session.beginTransaction();
			Teacher t1 = new Teacher();
			t1.setName("老张");
			session.save(t1);
			Teacher t2 = new Teacher();
			t2.setName("老刘");
			session.save(t2);
			Course c1 = new Course();
			c1.setName("数据结构");
			session.save(c1);
			Course c2 = new Course();
			c2.setName("计算机组成原理");
			session.save(c2);
			TeacherCourse tc1 = new TeacherCourse();
			tc1.setAch(87);
			tc1.setTeacher(t1);
			tc1.setCourse(c1);
			session.save(tc1);
			
			tc1 = new TeacherCourse();
			tc1.setAch(66);
			tc1.setTeacher(t1);
			tc1.setCourse(c2);
			session.save(tc1);
			
			tc1 = new TeacherCourse();
			tc1.setAch(190);
			tc1.setTeacher(t2);
			tc1.setCourse(c1);
			session.save(tc1);
			
			tc1 = new TeacherCourse();
			tc1.setAch(20);
			tc1.setTeacher(t2);
			tc1.setCourse(c2);
			session.save(tc1);
			session.getTransaction().commit();
		} catch (Exception e) {
			e.printStackTrace();
			if(session!=null) session.getTransaction().rollback();
		} finally {
			HibernateUtil.close(session);
		}
	}
	
	@Test
	public void testLoad01() {
		Session session = null;
		try {
			session = HibernateUtil.openSession();
			session.beginTransaction();
			Teacher t = (Teacher)session.load(Teacher.class, 1);
			//load的时候由于延迟加载，会根据不同的情况取相应的关联对象，所以会发出大量的sql
			/**
			 * 总体来说：最佳实践就是，一般不使用双向关联，特别不建议使用一的这一方的关联
			 * 因为从一的这一端取关联对象很有可能会涉及到分页操作，所以基本不会使用
			 * 在设计的时候不是特殊情况不要使用双向关联。
			 */
			System.out.println(t.getName());
			for(TeacherCourse tc:t.getTcs()) {
				System.out.println(tc.getCourse().getName()+":"+tc.getAch());
			}
			session.getTransaction().commit();
		} catch (Exception e) {
			e.printStackTrace();
			if(session!=null) session.getTransaction().rollback();
		} finally {
			HibernateUtil.close(session);
		}
	}