Hibernate 笔记 之 二 查询

1.Hibernate查询

　　1.1oid查询 即get　　　

Users users = session.get(Users.class, 1);

　　1.2对象属性导航查询

//对象属性导航查询
@Test
public void obj() {
    Session session = HibernateUtils.getCurrentSession();
    Transaction tx = session.beginTransaction();
    String name = session.get(Users.class,1)
                          .getClassroom().getClass_name();
    System.out.println(name);
    tx.commit();
}                

　　1.3HQL

public class Hql {
    /*
     * hql是hibernate独创的
     * hql语句中不会出现数据库的字段
     * hql是面向对象查询
     * hql使用的类名是全类名
     * 如果项目中没有重复类名的实体那么使用直接用类名
     */
    @Test
    //简单查询
    public void simpleHql() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        String hql="from Users";
        Query query = session.createQuery(hql);
        @SuppressWarnings("unchecked")
        List<Users> users = query.list();
        for (Users user : users) {
            System.out.println(user);
        }
        tx.commit();
    }
    
    @Test
    //指定条件查询
    public void parameterHql() {
        Session session = HibernateUtils.getCurrentSession();
        session.beginTransaction();
        String hql = "from Users where id=?";
        Query query = session.createQuery(hql);
        query.setParameter(0, 2);
        Users user = (Users) query.uniqueResult();
        System.out.println(user);
    }
    
    @Test
    //指定条件查询
    public void parameter2Hql() {
        Session session = HibernateUtils.getCurrentSession();
        session.beginTransaction();
        String hql = "from Users where id=:id";
        Query query = session.createQuery(hql);
        query.setParameter("id", 2);
        Users user = (Users) query.uniqueResult();
        System.out.println(user);
    }
    @SuppressWarnings("unchecked")
    @Test
    //分页
    public void limitHql() {
        Session session = HibernateUtils.getCurrentSession();
        session.beginTransaction();
        String hql = "from Users";
        Query query = session.createQuery(hql);
        query.setFirstResult(1);
        query.setMaxResults(1);
        List<Users> user = query.list();
        System.out.println(user);
    }
}

public class hql {
    /*
     * 在hql语句中在inner join 后带fetch的话是
     * 迫切查询
     * 迫切查询是查询返回是from后面的对象
     * 而不用的时候返回的是object数组
     */
    @Test
    //manyTomany
    public void hql1() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        String hql = "from Users u inner join fetch u.course ";
        Query query = session.createQuery(hql);
        List<Users> lists = query.list();
        for (Users users : lists) {
            System.out.println(users.getCourse());
        }
//        System.out.println(lists);
        tx.commit();
    }
    @Test
    //oneTomany
    public void hql2() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        String hql = "from Users u inner join  u.classroom";
        Query query = session.createQuery(hql);
        List<Object[]> list = query.list();
        /*for (Users users : list) {
            System.out.println(users);
        }*/
        tx.commit();
    }
}

　　1.4Criteria

public class CriteriaDemo {
    
    @Test
    //简单查询
    public void simpleCriteria() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        Criteria criteria = session.createCriteria(Users.class);
         List<Users> list = criteria.list();
        for (Users user : list) {
            System.out.println(user);
        }
        tx.commit();
    }
    @Test
    //带参数查询
    public void parameterCriteria() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        @SuppressWarnings("unchecked")
        List<Users> list = session.createCriteria(Users.class)
               .add(Restrictions.eq("id", 2))
               .list();
        for (Users users : list) {
            System.out.println(users);
        }
        tx.commit();
    }
    
    @Test
    //使用聚集函数
    public void parameter2Criteria() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        Criteria criteria = session.createCriteria(Users.class);
        criteria.setProjection(Projections.rowCount());
        Long result = (Long) criteria.uniqueResult();
        System.out.println(result);
        tx.commit();
        
    }
    @Test
    //分页
    public void limitCriteria() {
        
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        Criteria criteria = session.createCriteria(Users.class);
        criteria.setFirstResult(0);
        criteria.setMaxResults(1);
        List<Users> list = criteria.list();
        for (Users users : list) {
            System.out.println(users);
        }
        tx.commit();
    }
    @Test
    /*
     * 分离的criteria
     * 在没有session对象的方法中封装条件
     * 通过方法传参的方式将分离的criteria
     * 传递到数据库控制层
     */
    public void detached() {
        DetachedCriteria criteria = DetachedCriteria.forClass(Users.class);
        criteria.add(Restrictions.idEq(1));
        //-----------------------------------------------------------
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        Users result = (Users) criteria.getExecutableCriteria(session).uniqueResult();
        tx.commit();
        System.out.println(result);
    }
}