hibernate ?hql

1.什么是hql

Hibernate Query Language即Hibernate查询语言，面向的是类和属性

下面开始列子

//1.HQL 检索所有学生集合
@org.junit.Test
public void testselectAllDepts(){
 ???String hql="from Student";
 ???Query query = session.createQuery(hql);
 ???List<Student> list = query.list();
 ???for (Student student:list) {
 ???????System.out.println(student.getStuname());
 ???}
}

//2.获取学生的信息
@org.junit.Test
public void testselectSomeRows(){
 ???String hql="from Student d where d.stuname=‘呵呵‘";
 ???Query query = session.createQuery(hql);
 ???List<Student> list = query.list();
 ???for (Student student:list) {
 ???????System.out.println(student.getStuname());
 ???}
}

//3.获取部分列
@org.junit.Test
public void testgetMultiColumns(){
 ???String hql="select d.stuname from Student d";
 ???Query query = session.createQuery(hql);
 ???List<String> list = query.list();
 ???for (String dept:list) {
 ???????System.out.println(dept);
 ???}
}

//3.获取部分列 ?多列 ??List<Objecgt[]>
@Test
public void testgetMultipleColumns(){
 ???String hql="select d.stuname,d.sage from Student d";
 ???Query query = session.createQuery(hql);
 ???List<Object[]> list = query.list();
 ???for (Object[] dept:list) {
 ???????for (Object item:dept){
 ???????????System.out.print(item+"===");
 ???????}
 ???????System.out.println();
 ???}
}

  1.匿名占位符

from Student where stuname = ? 

  2.名称占位符

 from Student where s.stuname = :stuname 

3.绑定命名参数与一个对象的属性值

Session session = HibernateUtil.openSession();

NewsDetail news=new NewsDetail();

news.setNtitle("hibernate");

hibernate 工具类

public class HibernateUtil {

 ???// 初始化一个ThreadLocal对象
 ???@SuppressWarnings("rawtypes")
 ???private static final ThreadLocal sessionTL = new ThreadLocal();
 ???private static Configuration configuration;
 ???private final static SessionFactory sessionFactory;
 ???static {
 ???????try {
 ???????????configuration = new Configuration().configure();
 ???????????sessionFactory = configuration.buildSessionFactory();
 ???????} catch (Throwable ex) {
 ???????????throw new ExceptionInInitializerError(ex);
 ???????}
 ???}
 ???public static Session currentSession() {
 ???????//sessionTL的get()方法根据当前线程返回其对应的线程内部变量，
 ???????Session session = (Session) sessionTL.get();
 ???????// 如果session为null，则打开一个新的session
 ???????if (session == null) {
 ???????????//创建一个数据库连接对象session。
 ???????????session = sessionFactory.openSession();
 ???????????// 保存该数据库连接session到ThreadLocal中。
 ???????????sessionTL.set(session);
 ???????}
 ???????//sessionTL中get()可以获取该线程上次获取过的数据库连接对象。
 ???????return session;
 ???}
 ???/**
 ????* 关闭Session
 ????*/
 ???public static void closeSession(){
 ???????Session session = (Session) sessionTL.get();
 ???????sessionTL.set(null);
 ???????session.close();
 ???}

hql实现动态查询

1.检索条件的实体属性

//job
private String job;
//salary
private Double sal;

//入职开始时间
private Date fromDate;

//入职结束时间
private Date endDate;

   2.测试

@Test
public void test05() throws ParseException {
 ???/*准备对象*/
 ???Electronic ex=new Electronic();
 ???/*价格小于等于800.0*/
 ???ex.setPrice(800.0);
 ??/*准备hql，hql根据条件动态生成*/
 StringBuilder stringBuilder=new StringBuilder("from Electronic e where 1=1 "); ????

 /*判断价格是否为空*/
 if(ex.getPrice()!=null){
 ?????stringBuilder.append("and e.price<=:price");
 }
 /*3. 依据hql构建query对象*/
 ???Query query=session.createQuery(stringBuilder.toString());
 ???/*使用query对象的setProperties()方法为参数赋值，empCondition对象中封装了条件*/
 ???query.setProperties(ex);
 ???List<Electronic> list = query.list();
 ???/*遍历*/
 ???for (Electronic item:list) {
 ???????System.out.println(item.getEid()+"==="+item.getE_code()+"==="+item.getPrice());
 ???}
}

分页查询

uniqueResult()获取唯一对象

setFirstResult(int firstResult) 设置返回结果从第几条开始 ---- 索引从0开始

setMaxResults(int maxResults) 设置本次返回结果记录条数 

@Test
public void selectPageEc(){
 ???String hql="from Electronic";
 ???Query query = session.createQuery(hql);
 ???int pageSize=3;
 ???int pageIndex=1;
 ???query.setFirstResult((pageIndex-1)*pageSize); //6
 ???query.setMaxResults(pageSize);
 ???List<Electronic> list = query.list();
 ???for (Electronic item:list) {
 ???????System.out.println(item.getE_code());
 ???}
}