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Hibernate_12_HQL语句查询

www.someabcd.com  网友分享于:Jun 8, 2018 6:06:47 PM

标签:hibernate   java   session   实例   hql   

使用HQL查询的特点:

(1)与SQL相似,SQL中的语法基本上都可以直接使用。

(2)SQL查询的是表和表中的列;HQL查询的是对象与对象中的属

(3)HQL的关键字不区分大小写,类名与属性名是区分大小写

(4)SELECT可以省略.

Employee类、Department类、SessionFactoryTools类、Employee.hbm.xml文件、 Department.hbm.xml文件、Hibernate.cfg.xml文件都与4中的相同。

1>简单的数据库的查询:

持久化层代码:

/**
 * 员工类和部门类的持久层类
 */
public class EmpAndDepDao {
	/**
	 * save的方法
	 */
	@Test
	public void save() {
		Session session = SessionFactoryTools.getSession();			<span style="white-space:pre">						</span>Transaction tx = null;// 声明一个事务
		try {
			tx = session.beginTransaction();// 开始一个事务

			// ============================================
			// 新建部门对象,设置并设置部门名称
			for (int i = 0; i < 10; i++) {
				Department department = new Department();
				department.setName("开发部" + i);
				session.save(department);
			}

			// 新建员工对象,并设置姓名
			for (int i = 0; i < 20; i++) {
				Employee employee = new Employee();
				employee.setName("赵钱孙" + i);
				session.save(employee);
			}

			// ===============================================

			tx.commit();
		} catch (RuntimeException e) {
			if (tx != null) {
				tx.rollback();
			}
			throw e;
		} finally {
			session.close();
		}
	}

	/**
	 * getById
	 */
	@Test
	public void getById() {
		Session session = SessionFactoryTools.getSession();
		Transaction tx = null;
		try {
			tx = session.beginTransaction();
			String hql = null;
			// ================================================================

			// -------获取部门信息-------------------------------------
			
			/** 1,简单的查询
			 	hql = "FROM Employee";
			 	hql = "FROM Employee AS e"; // 使用别名
			 	hql = "FROM Employee e"; // 使用别名,as关键字可省略
			*/
			
			/** 2,带上过滤条件的(可以使用别名):Where
			 	hql = "FROM Employee WHERE id<10";
			 	hql = "FROM Employee e WHERE e.id<10";
			 	hql = "FROM Employee e WHERE e.id<10 AND e.id>5";
			*/
			
			/**3,带上排序条件的:Order By
				 hql = "FROM Employee e WHERE e.id<10 ORDER BY e.name";
				 hql = "FROM Employee e WHERE e.id<10 ORDER BY e.name DESC";
	        <span style="white-space:pre">		</span> hql = "FROM Employee e WHERE e.id<10 ORDER BY e.name DESC, id ASC";
		*/
			
		/**4,指定select子句(不可以使用select *)
			 hql = "SELECT e FROM Employee e"; // 相当于"FROM Employee e"
  			 // 只查询一个列,返回的集合的元素类型就是这个属性的类型
<span style="white-space:pre">			</span> hql = "SELECT e.name FROM Employee e"; 	
<span style="white-space:pre">			</span>// 查询多个列,返回的集合的元素类型是Object数组			 	<span style="white-space:pre">						</span>hql = "SELECT e.id,e.name FROM Employee e"; 
<span style="white-space:pre">			</span>// 可以使用new语法,指定把查询出的部分属性封装到对象中
<span style="white-space:pre">			</span>hql = "SELECT new Employee(e.id,e.name) FROM Employee e"; */
			
		/** 5,执行查询,获得结果(list、uniqueResult、分页 )
			Query query = session.createQuery("FROM Employee e WHERE id<3");
				 query.setFirstResult(0);
				 query.setMaxResults(10);
			// List list = query.list(); // 查询的结果是一个List集合
<span style="white-space:pre">			</span>// 查询的结果是唯一的一个结果,当结果有多个,就会抛异常
			Employee employee = (Employee) query.uniqueResult();			<span style="white-space:pre">						</span>System.out.println(employee);
		*/
			
		/** 6,方法链
			  List list = session.createQuery(//
					"FROM Employee")//
					.setFirstResult(0)//
					.setMaxResults(10)//
					.list();
		*/
			
			// -----赋值语句--------------------------------
		<span style="white-space:pre">	</span>hql = "SELECT new Employee (e.id,e.name) FROM Employee e";
			
			//-------执行查询-------------------------------
			List<?> list= session.createQuery(hql).list();
			
			// ----- 显示结果-----------------------------------
			/**
			 *  判断List为什么类型,
<span style="white-space:pre">			</span> *  若为数组类型则采用数组输出方式,
<span style="white-space:pre">			</span> *  否则采用对象输出方式
			*/
			for (Object obj : list) {
				if (obj.getClass().isArray()) {
				   System.out.println(Arrays.toString((Object[]) obj));
				} else {
					System.out.println(obj);
				}
			}
			
	   // =====================================================
			tx.commit();
		} catch (RuntimeException e) {
			tx.rollback();
			throw e;
		} finally {
			session.close();
		}
	}
}

2>带有限定条件和关联的数据库查询:

查询方法:

/**
	 * getById
	 */
	@Test
	public void getById() {
		Session session = SessionFactoryTools.getSession();
		Transaction tx = null;
		try {
			tx = session.beginTransaction();
			String hql = null;
			// ==================================================

			// -------获取部门信息-------------------------------

			/** 1,聚集函数:count(), max(), min(), avg(), sum() <span style="white-space:pre">													</span>// 返回的结果是Long型的
				 hql = "SELECT COUNT(*) FROM Employee"; 		
<span style="white-space:pre">				</span>// 返回的结果是id属性的类型		 		
<span style="white-space:pre">				</span>hql = "SELECT min(id) FROM Employee"; 
     <span style="white-space:pre">				</span> Number result = (Number) session.createQuery(hql).uniqueResult();
				 System.out.println(result.getClass());
				 System.out.println(result);
			*/
			
			/** 2,分组: Group By ... Having
	<span style="white-space:pre">			</span> hql = "SELECT e.name,COUNT(e.id) FROM Employee e GROUP BY e.name";
	<span style="white-space:pre">			</span> hql = "SELECT e.name,COUNT(e.id) FROM Employee e GROUP BY e.name HAVING count(e.id)>1";
	 <span style="white-space:pre">			</span> hql = "SELECT e.name,COUNT(e.id) FROM Employee e WHERE id<9 GROUP BY e.name HAVING count(e.id)>1";
	<span style="white-space:pre">	</span>	         //------链式查询语言-------------------------
				 hql = "SELECT e.name,COUNT(e.id) " + //
				 "FROM Employee e " + //
				 "WHERE id<9 " + //
				 "GROUP BY e.name " + //
				 "HAVING count(e.id)>1 " + //
				 "ORDER BY count(e.id) ASC";
				 ---
				 hql = "SELECT e.name,COUNT(e.id) AS c " + //
				 "FROM Employee e " + //
				 "WHERE id<9 " + //
				 "GROUP BY e.name " + //
		<span style="white-space:pre">		</span> "HAVING count(e.id)>1 " + // 在having子句中不能使用列别名
				 "ORDER BY c ASC"; // 在orderby子句中可以使用列别名
			*/
			
			/** 3,连接查询 / HQL是面向对象的查询
				 //内连接(inner关键字可以省略)
				 hql = "SELECT e.id,e.name,d.name FROM Employee e INNER JOIN e.department d";
				 hql = "SELECT e.id,e.name,d.name FROM Employee e JOIN e.department d";
				 // 左外连接(outer关键字可以省略)
				 hql = "SELECT e.id,e.name,d.name FROM Employee e LEFT OUTER JOIN e.department d";
				 hql = "SELECT e.id,e.name,d.name FROM Employee e LEFT JOIN e.department d";
				 // 右外连接(outer关键字可以省略)
				 hql = "SELECT e.id,e.name,d.name FROM Employee e RIGHT OUTER JOIN e.department d";
				  hql = "SELECT e.id,e.name,d.name FROM Employee e RIGHT JOIN e.department d";
				 // 可以使用更方便的方法
				 hql = "SELECT e.id,e.name,e.department.name FROM Employee e";
			*/
			
			/** 4,查询时使用参数
				 //方式一:使用'?'占位
				 hql = "FROM Employee e WHERE id BETWEEN ? AND ?";
				 List list = session.createQuery(hql)//
				 .setParameter(0, 5)// 设置参数,0表示为第一个参数
				 .setParameter(1, 15)//1表示为第二个参数
				 .list();
			
			
				//方式二:使用变量名
				 hql = "FROM Employee e WHERE id BETWEEN :idMin AND :idMax";
				 List list = session.createQuery(hql)//
				 .setParameter("idMax", 15)//idMax表示:上边缘
				 .setParameter("idMin", 5)//idMin表示:下边缘
				 .list();

			// 当参数是集合时,一定要使用setParameterList()设置参数值
				 hql = "FROM Employee e WHERE id IN (:ids)";
			List list = session.createQuery(hql)//ids表示:变量名
		<span style="white-space:pre">		</span>    <span style="white-space:pre">	</span>.setParameterList("ids", new Object[] { 1, 2, 3, 5, 8, 100 })
				 <span style="white-space:pre">	</span>.list();//数组中的数值为变量名可以取得数值
			*/
			
			/** 5,使用命名查询
			 * 	 //需要在hbm文件中配置查询语句
			     //queryByIdRange:hbm文件中配置的查询语句的名称
				 Query query = session.getNamedQuery("queryByIdRange");
				 query.setParameter("idMin", 3);
    <span style="white-space:pre">				</span>//idMin、idMax:查询语句中的变量名
				 query.setParameter("idMax", 10);
				 List list = query.list();
			*/
			
		   /**6,update与delete,不会通知Session缓存
				//Update
				 int result = session.createQuery(//
				 		"UPDATE Employee e SET e.name=? WHERE id>15")//
				 		.setParameter(0, "无名氏")//
				 		.executeUpdate(); // 返回int型的结果,表示影响了多少行。
				 System.out.println("result = " + result);
				//Delete
				int result = session.createQuery(//
						"DELETE FROM Employee e WHERE id>15")//
						.executeUpdate(); // 返回int型的结果,表示影响了多少行。
				System.out.println("result = " + result);
		  */
			
		  // ----- 执行查询并显示结果----------------------------
			 
			 List list = session.createQuery(hql).list();
			 
			 for (Object obj : list) {
				 if (obj.getClass().isArray()) {
					 System.out.println(Arrays.toString((Object[]) obj));
				 } else {
					 System.out.println(obj);
				 }
			 }

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

 注意:在updatedelete后,需要refresh(obj)一下以获取最新的状态

// 第一次显示名称
	   Employee employee = (Employee) session.get(Employee.class, 1);
		System.out.println(employee.getName());

		// update与delete,不会通知Session缓存
		int result = session.createQuery(//
				"UPDATE Employee e SET e.name=? WHERE id=1")//
				.setParameter(0, "无名氏2")//
				.executeUpdate(); 
		System.out.println(result);
		// 第二次显示名称
		session.refresh(employee);
		System.out.println(employee.getName());






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Hibernate_12_HQL语句查询

标签:hibernate   java   session   实例   hql   

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