Hibernate的Query接口和查询操作

Hibernate基本查询

Qurey接口：Hibernate专门用来执行HQL语句的查询接口

使用方式：

Query query=session.createQuery("HQL");
query.setParameter("");
List resultList=query.list();

HQL(Hibernate Query Language)

功能：

1.  条件查询
2. 支持投影下旬
3. 分页查询
4. 连接查询
5. 分组查询
6. 子查询
7. 内置聚合函数
8. 支持动态绑定参数

查询实体类的所有实例对象

    @Test
    public void queryAll() {
        Session session=HandleSession.getSession();
        Transaction transaction=session.beginTransaction();

        try{
            String hql="from Student ";

            Query query=session.createQuery(hql);// or "select stu from Student as stu"

            List list=(List) query.list();
            for(Student student:list){
                System.out.println(student);
            }
            transaction.commit();
        }catch (Exception e){

            if(transaction!=null){
                transaction.rollback();
            }

            e.printStackTrace();
        }finally {

            session.close();
        }
    }

    @Test
    public void querySingle(){
        Session session=HandleSession.getSession();
        Transaction transaction=session.beginTransaction();

        try{
            String hql="from Student ";
            Student student=(Student) session.createQuery(hql).setMaxResults(1).uniqueResult();
            System.out.println(student);
            transaction.commit();
        }catch (Exception e){

            if(transaction!=null){
                transaction.rollback();
            }

            e.printStackTrace();
        }finally {

            session.close();
        }
    }

投影查询：查询类的几个属性，通过用select语句只选择类的部分属性来实现：

Query query=session.createQuery("SELECT id,name FROM Student");
List list=query.list()

	public void queryShadow(){
        Session session=HandleSession.getSession();
        Transaction transaction=session.beginTransaction();

        try{
            String hql="select a.name,a.age from Student a";
            Query query=session.createQuery(hql);
            List list=query.list();
            for(Object[] objects:list){
               for(Object object:objects)
                   System.out.println(object);
            }
            transaction.commit();
        }catch (Exception e){

            if(transaction!=null){
                transaction.rollback();
            }

            e.printStackTrace();
        }finally {

            session.close();
        }
    }

查询实例：添加相应的构造方法

在Student类中添加构造方法：

public Student(String name,int age){
    this.name=name;
    this.age=age;
}

	@Test
    public void queryShadow2(){
        Session session=HandleSession.getSession();
        Transaction transaction=session.beginTransaction();

        try{
            String hql="select new Student (a.name,a.age) from Student a";
            Query query=session.createQuery(hql);
            List list=query.list();
            for(Student student:list)
                    System.out.println(student);
            
            transaction.commit();
        }catch (Exception e){

            if(transaction!=null){
                transaction.rollback();
            }

            e.printStackTrace();
        }finally {
            session.close();
        }
    }

where条件语句：查询符合条件的对象

.号

比较运算符：=,<,>,<=,>=,is null,is not null

范围运算符:in,not in,between  and,not between and

模式匹配符：like'模式字符串' 其中可用‘%’代替任意长度字符串，'_'代表单个字符

逻辑运算符:and,not,or

用于集合的运算符：is empty,is not empty

HQL常见函数：

字符串相关：upper(s),lower(s),concat(s1,s2),substring(s,offset,length),length(s)

trim(s),locate(search,s,offset)

数字：abs(n),sort(n),mod(dividend,divisor)

集合:size(c) 返回集合中元素的个数

日期时间：current_date(),current_time(),current_timestamp(),

year(d),moth(d),day(d),hour(d),minute(d),second(d)

distinct:去掉相同的数据项

oder by:desc 按倒序排列，asc按升序排列

参数绑定：where字句中经常需要动态设置查询函数，Hibernate提供了两种绑定参数的方式

按参数名字绑定

按参数位置绑定

    @Test
    public void queryArguments(){
        Session session=HandleSession.getSession();
        Transaction transaction=session.beginTransaction();

        try{

            /*按参数名字绑定
            *  String hql="select new Student (stu.name,stu.age)from Student as stu where stu.name=? and stu.age=?";

            Query query=session.createQuery(hql);
            query.setString(0,"wang");
            query.setInteger(1,21);
            * */
            /*按参数名字绑定*/
            String hql="select new Student (stu.name,stu.age)from Student as stu where stu.name=:name and stu.age=:age";

            Query query=session.createQuery(hql);
            query.setString("name","wang");
            query.setInteger("age",21);
            List list=query.list();
            for(Student student:list)
                System.out.println(student);

            transaction.commit();
        }catch (Exception e){

            if(transaction!=null){
                transaction.rollback();
            }

            e.printStackTrace();
        }finally {
            session.close();
        }
    }

聚合函数：查询结果作为Long返回

count(),avg(),sum(),max(),min()

    @Test
    public void queryCount(){
        Session session=HandleSession.getSession();
        Transaction transaction=session.beginTransaction();
        try{
            /*String hql="select count(stu.id)from Student as stu";*/
            String hql="select max(stu.age)from Student as stu";

            Query query=session.createQuery(hql);
            List list=query.list();
            System.out.println(list.get(0));
            transaction.commit();
        }catch (Exception e){

            if(transaction!=null){
                transaction.rollback();
            }

            e.printStackTrace();
        }finally {
            session.close();
        }
    }

group by:对查询的数据，根据条件进行分组，常与聚合函数配合使用

    @Test
    public void queryCount(){
        Session session=HandleSession.getSession();
        Transaction transaction=session.beginTransaction();
        try{
            //按班级查询每个班的人数
            String hql="select count(stu.id),stu.class from Student as stu group by stu.class";
            Query query=session.createQuery(hql);
            List list=query.list();
            for(Object[] objects:list)
            for(Object object:objects)
                System.out.println(object);
            transaction.commit();
        }catch (Exception e){

            if(transaction!=null){
                transaction.rollback();
            }

            e.printStackTrace();
        }finally {
            session.close();
        }
    }

having关键字与group by配合使用，对分组查询后的数据进行过滤

分页查询：Query接口提供了以下两个用于分页显示查询结果的方法

setFirstResult(int firstResult);

setMaxResult(int maxResult);