• Hibernate 笔记 之 二 查询


    1.Hibernate查询

      1.1oid查询 即get   

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

      1.2对象属性导航查询

     1 //对象属性导航查询
     2 @Test
     3 public void obj() {
     4     Session session = HibernateUtils.getCurrentSession();
     5     Transaction tx = session.beginTransaction();
     6     String name = session.get(Users.class,1)
     7                           .getClassroom().getClass_name();
     8     System.out.println(name);
     9     tx.commit();
    10 }                
    对象属性导航查询

      1.3HQL

     1 public class Hql {
     2     /*
     3      * hql是hibernate独创的
     4      * hql语句中不会出现数据库的字段
     5      * hql是面向对象查询
     6      * hql使用的类名是全类名
     7      * 如果项目中没有重复类名的实体那么使用直接用类名
     8      */
     9     @Test
    10     //简单查询
    11     public void simpleHql() {
    12         Session session = HibernateUtils.getCurrentSession();
    13         Transaction tx = session.beginTransaction();
    14         String hql="from Users";
    15         Query query = session.createQuery(hql);
    16         @SuppressWarnings("unchecked")
    17         List<Users> users = query.list();
    18         for (Users user : users) {
    19             System.out.println(user);
    20         }
    21         tx.commit();
    22     }
    23     
    24     @Test
    25     //指定条件查询
    26     public void parameterHql() {
    27         Session session = HibernateUtils.getCurrentSession();
    28         session.beginTransaction();
    29         String hql = "from Users where id=?";
    30         Query query = session.createQuery(hql);
    31         query.setParameter(0, 2);
    32         Users user = (Users) query.uniqueResult();
    33         System.out.println(user);
    34     }
    35     
    36     @Test
    37     //指定条件查询
    38     public void parameter2Hql() {
    39         Session session = HibernateUtils.getCurrentSession();
    40         session.beginTransaction();
    41         String hql = "from Users where id=:id";
    42         Query query = session.createQuery(hql);
    43         query.setParameter("id", 2);
    44         Users user = (Users) query.uniqueResult();
    45         System.out.println(user);
    46     }
    47     @SuppressWarnings("unchecked")
    48     @Test
    49     //分页
    50     public void limitHql() {
    51         Session session = HibernateUtils.getCurrentSession();
    52         session.beginTransaction();
    53         String hql = "from Users";
    54         Query query = session.createQuery(hql);
    55         query.setFirstResult(1);
    56         query.setMaxResults(1);
    57         List<Users> user = query.list();
    58         System.out.println(user);
    59     }
    60 }
    单表HQL
     1 public class hql {
     2     /*
     3      * 在hql语句中在inner join 后带fetch的话是
     4      * 迫切查询
     5      * 迫切查询是查询返回是from后面的对象
     6      * 而不用的时候返回的是object数组
     7      */
     8     @Test
     9     //manyTomany
    10     public void hql1() {
    11         Session session = HibernateUtils.getCurrentSession();
    12         Transaction tx = session.beginTransaction();
    13         String hql = "from Users u inner join fetch u.course ";
    14         Query query = session.createQuery(hql);
    15         List<Users> lists = query.list();
    16         for (Users users : lists) {
    17             System.out.println(users.getCourse());
    18         }
    19 //        System.out.println(lists);
    20         tx.commit();
    21     }
    22     @Test
    23     //oneTomany
    24     public void hql2() {
    25         Session session = HibernateUtils.getCurrentSession();
    26         Transaction tx = session.beginTransaction();
    27         String hql = "from Users u inner join  u.classroom";
    28         Query query = session.createQuery(hql);
    29         List<Object[]> list = query.list();
    30         /*for (Users users : list) {
    31             System.out.println(users);
    32         }*/
    33         tx.commit();
    34     }
    35 }
    多表

      1.4Criteria

     1 public class CriteriaDemo {
     2     
     3     @Test
     4     //简单查询
     5     public void simpleCriteria() {
     6         Session session = HibernateUtils.getCurrentSession();
     7         Transaction tx = session.beginTransaction();
     8         Criteria criteria = session.createCriteria(Users.class);
     9          List<Users> list = criteria.list();
    10         for (Users user : list) {
    11             System.out.println(user);
    12         }
    13         tx.commit();
    14     }
    15     @Test
    16     //带参数查询
    17     public void parameterCriteria() {
    18         Session session = HibernateUtils.getCurrentSession();
    19         Transaction tx = session.beginTransaction();
    20         @SuppressWarnings("unchecked")
    21         List<Users> list = session.createCriteria(Users.class)
    22                .add(Restrictions.eq("id", 2))
    23                .list();
    24         for (Users users : list) {
    25             System.out.println(users);
    26         }
    27         tx.commit();
    28     }
    29     
    30     @Test
    31     //使用聚集函数
    32     public void parameter2Criteria() {
    33         Session session = HibernateUtils.getCurrentSession();
    34         Transaction tx = session.beginTransaction();
    35         Criteria criteria = session.createCriteria(Users.class);
    36         criteria.setProjection(Projections.rowCount());
    37         Long result = (Long) criteria.uniqueResult();
    38         System.out.println(result);
    39         tx.commit();
    40         
    41     }
    42     @Test
    43     //分页
    44     public void limitCriteria() {
    45         
    46         Session session = HibernateUtils.getCurrentSession();
    47         Transaction tx = session.beginTransaction();
    48         Criteria criteria = session.createCriteria(Users.class);
    49         criteria.setFirstResult(0);
    50         criteria.setMaxResults(1);
    51         List<Users> list = criteria.list();
    52         for (Users users : list) {
    53             System.out.println(users);
    54         }
    55         tx.commit();
    56     }
    57     @Test
    58     /*
    59      * 分离的criteria
    60      * 在没有session对象的方法中封装条件
    61      * 通过方法传参的方式将分离的criteria
    62      * 传递到数据库控制层
    63      */
    64     public void detached() {
    65         DetachedCriteria criteria = DetachedCriteria.forClass(Users.class);
    66         criteria.add(Restrictions.idEq(1));
    67         //-----------------------------------------------------------
    68         Session session = HibernateUtils.getCurrentSession();
    69         Transaction tx = session.beginTransaction();
    70         Users result = (Users) criteria.getExecutableCriteria(session).uniqueResult();
    71         tx.commit();
    72         System.out.println(result);
    73     }
    74 }
    单表Criteria
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  • 原文地址:https://www.cnblogs.com/FlyBlueSky/p/9147436.html
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