hibernate 之 hibernate查询

1. hibernate 提供了多种查询方式，使得可以更好的适应各种应用场景，常见的有，hql查询，本地sql查询， Criteria查询等。

2. hql:hibernate query  language， hibernate查询语言，它是一种完全面向对象的查询语言，在hql中，关键字时不区分大小写的，而类名和属性名时区分大小写的。

3.查询案例：

　　

public class HqlTest {
    private Session session=null;
    @Before
    public void setUp(){
        session = HibernateUtil.getSession();
    }
    @After
    public void tearDown(){
        HibernateUtil.close();
    }
    @Test
    public void testCreateDB(){
        Configuration cfg = new Configuration().configure();
        SchemaExport export = new SchemaExport(cfg);
        //第一个参数  是否打印  数据库脚本
        //第二个参数 是否将脚本导入数据库执行
        export.create(true, true);
    }
    //查询所有
    @Test
    public void testFindAll(){
        //该hql语言等同于select * from t_student
        //hql中Student是类名
        String hql="from Student";
        //createQuery指使用hql查询
        List<Student> list = session.createQuery(hql).list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //条件查询
    @Test
    public void testCondition(){
        //如果是条件查询 可以在hql中添加查询的条件
        //在hql中添加别名的方式和sql一样  可以使用空格也可以使用as
        String hql="from Student s where s.age<40";
        List<Student> list = session.createQuery(hql).list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //使用占位符的条件查询
    @Test
    public void testConditionParam(){
        String hql="from Student s where s.age<?";
        List<Student> list = session.createQuery(hql)
                        .setInteger(0, 40)//为占位符设置参数 下标从0开始
                        .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //使用指定名称来进行条件查询
    @Test
    public void testConditionNameParam(){
        //使用名称来代表参数时 需要在名称前加冒号“:”
        String hql="from Student s where s.age<:age";
        List<Student> list = session.createQuery(hql)
                        .setInteger("age", 40)//为指定名称的参数设置
                        .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //查询多条件
    @Test
    public void testConditionNameParams(){
        //使用名称来代表参数时 需要在名称前加冒号“:”
        String hql="from Student s where s.age<:age and s.sex=:sex";
        Map<String,Object> map = new HashMap<String,Object>();
        map.put("age", 40);
        map.put("sex", "女");
        List<Student> list = session.createQuery(hql)
                        .setProperties(map)
                        .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //查询指定列
    @Test
    public void testColumn(){
        String hql="select s.name,s.sex from Student s";
        List<Object[]> list =session.createQuery(hql).list();
        for(Object[] objs:list){
            System.out.println(objs[0]+"----"+objs[1]);
        }
    }
    //查询指定列 并且将返回值封装
    @Test
    public void testColumnObject(){
        String hql="select new Student(s.name,s.sex) from Student s";
        List<Student> list = session.createQuery(hql)
                .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //分页查询
    @Test
    public void testPage(){
        String hql="from Student";
        List<Student> list = session.createQuery(hql)
                            .setFirstResult(0)//(currentPage-1)*pageSize
                            .setMaxResults(2)//pageSize
                            .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //uniqueResult  当结果唯一时 使用uniqueResult返回一个对象
    @Test
    public void testUniqueResult(){
        String hql="from Student where id=1";
        Student stu=(Student)session.createQuery(hql).uniqueResult();
        System.out.println(stu);
    }
    //聚合查询
    @Test
    public void testCount(){
        String hql="select count(id) from Student";
        Long result = (Long)session.createQuery(hql).uniqueResult();
        System.out.println(result);
    }
    //in子查询
    @Test
    public void testIn(){
        String hql="from Student where id in(:ids)";
        List<Student> list = session.createQuery(hql)
                            .setParameterList("ids", new Integer[]{1,2})
                            .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //模糊查询
    @Test
    public void testLike(){
        String hql="from Student where name like :name";
        List<Student> list = session.createQuery(hql)
                .setString("name", ("h"+"%"))
                .list();
        for(Student s:list){
        System.out.println(s);
        }
    }
    //关联查询
    @Test
    public void testJoin(){
        String hql="from Student s where s.teacher.name=:name";
        List<Student> list = session.createQuery(hql)
                            .setString("name", "nico")
                            .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //外联
    @Test
    public void testLeftOuterJoin(){
        String hql="select new Student(s.id,s.name,s.sex,s.age) from Student s left join s.teacher";
        List<Student> list = session.createQuery(hql)
                .list();
        for(Student s:list){
        System.out.println(s);
        }
    }
    //命名查询
    //需要在映射文件中 添加映射信息
    /**
     * 名称在应用中唯一
         <query name="findStudent">
        from Student
        </query>
     */
    @Test
    public void testNamedQuery(){
        List<Student> list = session.getNamedQuery("findStudent")
                .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
}

4. 本地sql 查询，hql语句是hibernate提供查询语言，hibernate可以跨数据库平台，但是hibernate不能使用某个特定数据库的特定功能，使用本地sql可以解决这个问题。

public class SqlTest {
    private Session session=null;
    @Before
    public void setUp(){
        session = HibernateUtil.getSession();
    }
    @After
    public void tearDown(){
        HibernateUtil.close();
    }
    //查询所有
    @Test
    public void testFindAll(){
        String sql="select * from t_student";
        List<Object[]> list = session.createSQLQuery(sql)
                                .list();
        for(Object[] objs:list){
            System.out.println(objs[1]+"----"+objs[2]);
        }
    }
    //查询后封装为对象
    @Test
    public void testFindObject(){
        String sql="select * from t_student";
        List<Student> list = session.createSQLQuery(sql)
                                .addEntity(Student.class)
                                .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //查询指定列时----返回的是数组 
    @Test
    public void testColumn(){
        String sql="select name,sex from t_student";
        List<Object[]> list = session.createSQLQuery(sql)
                                .list();
        for(Object[] objs:list){
            System.out.println(objs[0]+"----"+objs[1]);
        }
    }
    //条件查询
    @Test
    public void testCondition(){
        String sql="select * from t_student where age<:age";
        List<Student> list=session.createSQLQuery(sql)
                    .addEntity(Student.class)
                    .setInteger("age", 40)
                    .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //本地命名查询
    @Test
    public void testFindStudents(){
        List<Object[]> list =  session.getNamedQuery("findStudents")
                                    .list();
        for(Object[] objs:list){
            System.out.println(objs[0]+"----"+objs[1]);
        }
    }
    //分页
    @Test
    public void testPage(){
        String sql="select * from t_student";
        List<Student> list = session.createSQLQuery(sql)
                            .addEntity(Student.class)
                            .setFirstResult(0)
                            .setMaxResults(2)
                            .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
}

5. 对象查询 Criteria 查询：

public class CriteriaTest {
    private Session session=null;
    @Before
    public void setUp(){
        session = HibernateUtil.getSession();
    }
    @After
    public void tearDown(){
        HibernateUtil.close();
    }
    //查询所有
    @Test
    public void testFindAll(){
        List<Student> list = session.createCriteria(Student.class)
                                .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //条件查询
    @Test
    public void testCodition(){
        List<Student> list=session.createCriteria(Student.class)
                                .add(Restrictions.lt("age", 40))
                                .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //多条件查询
    @Test
    public void testCoditions(){
        List<Student> list=session.createCriteria(Student.class)
                                .add(Restrictions.lt("age", 40))
                                .add(Restrictions.eq("sex", "女"))
                                .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //或查询
    @Test
    public void testCoditionOr(){
        List<Student> list=session.createCriteria(Student.class)
                                .add(Restrictions.or(
                                Restrictions.lt("age", 40),
                                Restrictions.eq("sex", "女")))
                                .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //与或查询
    @Test
    public void testCoditionAndOr(){
        List<Student> list=session.createCriteria(Student.class)
                                .add(Restrictions.or(
                                Restrictions.and(
                                        Restrictions.lt("age", 40), 
                                        Restrictions.eq("sex", "男")),
                                Restrictions.eq("sex", "女")))
                                .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //模糊查询
    @Test
    public void testLike(){
        List<Student> list = session.createCriteria(Student.class)
                            .add(Restrictions.like("name", "h", MatchMode.START))
                            .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //排序
    @Test
    public void testOrder(){
        List<Student> list = session.createCriteria(Student.class)
                            .addOrder(Order.asc("age"))
                            .list();
        for(Student s:list){
            System.out.println(s);
        }
    }
    //聚合查询
    @Test
    public void testCount(){
        Long result = (Long)session.createCriteria(Student.class)
                            .setProjection(Projections.rowCount())
                            .uniqueResult();
        System.out.println(result);
    }
    //分页
    @Test
    public void testPage(){
        List<Student> list = session.createCriteria(Student.class)
                                .setFirstResult(0)
                                .setMaxResults(2)
                                .list();
        for(Student s:list){
        System.out.println(s);
        }
    }
    //关联查询
    @Test
    public void testJoin(){
        List<Student> list = session.createCriteria(Student.class)
                                    .createAlias("teacher", "t")
                                    .add(Restrictions.eq("t.id", 1))
                                    .list();
        for(Student s:list){
            System.out.println(s);
            }
    }
}