HQL (九) 连接查询

连接查询（重要）
* 内连接
* 外连接（左连接/右连接）
参见：JoinQueryTest.java

内连接有三种：inner join ，join，“=”

package com.wlh.hibernate;

import java.util.Iterator;
import java.util.List;

import junit.framework.TestCase;

import org.hibernate.Session;

public class JoinQueryTest extends TestCase{
	
	/**
	 * 内联结
	 */
	public void testQuery1() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			session.beginTransaction();
			 //====关键字join==========//
			List students=session.createQuery("select s.name ,c.name from Student s join s.classes c").list();
			for(Iterator iter=students.iterator();iter.hasNext();){
				Object [] o=(Object [])iter.next();
				System.out.println("id="+o[0]+",o[1]"+o[0]);
			}
			session.getTransaction().commit();
		}catch(Exception e) {
			e.printStackTrace();
			session.getTransaction().rollback();
		}finally {
			HibernateUtils.closeSession(session);
		}
	}	
	
	/**
	 * 内联结
	 */
	public void testQuery2() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			session.beginTransaction();
			 //=======关键字inner join 默认就是内连接，所以inner可以加上，也可以省略======//
			List students=session.createQuery("select s.name, c.name from Student s inner join s.classes c").list();
			for(Iterator iter=students.iterator();iter.hasNext();){
				Object [] o=(Object [])iter.next();
				System.out.println("id="+o[0]+",o[1]"+o[0]);
			}
			session.getTransaction().commit();
		}catch(Exception e) {
			e.printStackTrace();
			session.getTransaction().rollback();
		}finally {
			HibernateUtils.closeSession(session);
		}
	}	
	
	/**
	 * 内联结
	 */
	public void testQuery3() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			session.beginTransaction();
			//===========用"="实现内联===========//
			List students=session.createQuery("select s.name ,c.name from Student s ,Classes c where s.classes.id=c.id").list();
			for(Iterator iter=students.iterator();iter.hasNext();){
				Object [] o=(Object [])iter.next();
				System.out.println("id="+o[0]+",o[1]"+o[0]);
			}
			session.getTransaction().commit();
		}catch(Exception e) {
			e.printStackTrace();
			session.getTransaction().rollback();
		}finally {
			HibernateUtils.closeSession(session);
		}
	}	
	

[b][color=red]外联接：能够查出2个表之间不相互关联的记录[/color]	[/b]
         



  

    /**

	 * 外联结

	 */

	public void testQuery4() {

		Session session = null;

		try {

			session = HibernateUtils.getSession();

			session.beginTransaction();

			//查询出所有的学生（包括没有班级的学生）

			List students=session.createQuery("select s.name ,c.name from Student s  left join s.classes c").list();

			for(Iterator iter=students.iterator();iter.hasNext();){

				Object [] o=(Object [])iter.next();

				System.out.println("id="+o[0]+",o[1]="+o[1]);

			}

			session.getTransaction().commit();

		}catch(Exception e) {

			e.printStackTrace();

			session.getTransaction().rollback();

		}finally {

			HibernateUtils.closeSession(session);

		}

	}	

	

	

	

	/**

	 * 外联结

	 */

	public void testQuery5() {

		Session session = null;

		try {

			session = HibernateUtils.getSession();

			session.beginTransaction();

			//查询出所有的班级，（包括没有学生的班级）

			List students=session.createQuery("select s.name ,c.name from Student s  right join s.classes c").list();

			for(Iterator iter=students.iterator();iter.hasNext();){

				Object [] o=(Object [])iter.next();

				System.out.println("id="+o[0]+",o[1]="+o[1]);

			}

			session.getTransaction().commit();

		}catch(Exception e) {

			e.printStackTrace();

			session.getTransaction().rollback();

		}finally {

			HibernateUtils.closeSession(session);

		}

	}	

	

	

}