Hibernate 是一个开源免费的、基于 ORM 技术的 Java 持久化框架，它能够自动生成的 SQL 语句并自动执行，实现对数据库进行操作，整个过程完全不需要人工干预，大大降低了开发成本。那hibernate查询方式有哪些?下面来我们就来给大家讲解一下。
一、HQL查询
HQL(Hibernate Query Language)提供了丰富灵活的查询方式，使用HQL进行查询也是Hibernate官方推荐使用的查询方式。
HQL在语法结构上和SQL语句十分的相同，所以可以很快的上手进行使用。使用HQL需要用到Hibernate中的Query对象，该对象专门执行HQL方式的操作。
查询所有示例
session.beginTransaction();
String hql = "from User"; // from 后跟的是要查询的对象，而不是表
Query query = session.createQuery(hql);
List < User > userList = query.list();
for (User user: userList)
{
System.out.println(user.getUserName());
}
session.getTransaction()
.commit();带where的查询示例
session.beginTransaction();
String hql = "from User where userName = 'James'";
Query query = session.createQuery(hql);
List < User > userList = query.list();
for (User user: userList)
{
System.out.println(user.getUserName());
}
session.getTransaction()
.commit();
/*
在HQL中where语句中使用的是持久化对象的属性名，如上面示例中的userName。当然在HQL中也可以使用别名
*/
String hql = "from User as u where u.userName = 'James'";
/*
过滤条件
在where语句中还可以使用各种过滤条件，如：=、<>、<、>、>=、<=、between、not between、
in、not in、is、like、and、or等
*/获取一个不完整的对象
session.beginTransaction();
String hql = "select userName from User";
Query query = session.createQuery(hql);
List < Object > nameList = query.list();
for (Object obj: nameList)
{
String name = (String) obj;
System.out.println(name);
}
session.getTransaction()
.commit();
// 多个属性的话，需要用object[]接收
session.beginTransaction();
String hql = "select userName,userPwd from User";
Query query = session.createQuery(hql);
List nameList = query.list();
for (Object obj: nameList)
{
Object[] array = (Object[]) obj; // 转成object[]
System.out.println("name:" + array[0]);
System.out.println("pwd:" + array[1]);
}
session.getTransaction()
.commit();统计和分组查询
session.beginTransaction();
String hql = "select count(*),max(id) from User";
Query query = session.createQuery(hql);
List nameList = query.list();
for (Object obj: nameList)
{
Object[] array = (Object[]) obj;
System.out.println("count:" + array[0]);
System.out.println("max:" + array[1]);
}
session.getTransaction()
.commit();
/*
该条sql语句返回的是单条数据，所以还可以这样写
单列数据用Object，多列数据用Object[]
*/
Object[] object = (Object[]) query.uniqueResult();
System.out.println("count:" + object[0]);
System.out.println("max:" + object[1]);更多写法
select distinct name from Student; select max(age) from Student; select count(age), age from Student group by age; from Student order by age;
HQL占位符
session.beginTransaction();
String hql = "from User where userName = ?";
Query query = session.createQuery(hql);
// 索引从0开始
query.setString(0, "James");
List < User > userList = query.list();
for (User user: userList)
{
System.out.println(user.getUserName());
}
session.getTransaction()
.commit();HQL引用占位符
session.beginTransaction();
String hql = "from User where userName = :name";
Query query = session.createQuery(hql);
query.setParameter("name", "James");
List < User > userList = query.list();
for (User user: userList)
{
System.out.println(user.getUserName());
}
session.getTransaction()
.commit();HQL分页
session.beginTransaction();
String hql = "from User";
Query query = session.createQuery(hql);
query.setFirstResult(0);
query.setMaxResults(2);
List < User > userList = query.list();
for (User user: userList)
{
System.out.println(user.getUserName());
}
session.getTransaction()
.commit();二、QBC(Query By Criteria)查询
Criteria对象提供了一种面向对象的方式查询数据库。Criteria对象需要使用Session对象来获得。
一个Criteria对象表示对一个持久化类的查询。
查询所有
session.beginTransaction();
Criteria c = session.createCriteria(User.class);
List < User > userList = c.list();
for (User user: userList)
{
System.out.println(user.getUserName());
}
session.getTransaction()
.commit();where
session.beginTransaction();
Criteria c = session.createCriteria(User.class);
c.add(Restrictions.eq("userName", "James"));
List < User > userList = c.list();
for (User user: userList)
{
System.out.println(user.getUserName());
}
session.getTransaction()
.commit();Restrictions对象
方法名称 对应SQL中的表达式 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- Restrictions.eq field = value Restrictions.gt field > value Restrictions.lt field < value Restrictions.ge field >= value Restrictions.le field <= value Restrictions.between field between value1 and value2 Restrictions.in field in (…) Restrictions.and and Restrictions.or or Restrictions.like field like value
示例
1. Criteria c =
session.createCriteria(User.class);
2. c.add(Restrictions.like("userName",
"J"));
3. c.add(Restrictions.eq("id", 120));
4.
c.add(Restrictions.or(Restrictions.eq("userName", "James"),
5.
Restrictions.eq("userName", "Alex")));获取唯一记录
session.beginTransaction();
Criteria c = session.createCriteria(User.class);
c.add(Restrictions.eq("id", 120));
User user = (User) c.uniqueResult();
System.out.println(user.getUserName());
session.getTransaction()
.commit();分页
Criteria c = session.createCriteria(User.class); c.setFirstResult(0); c.setMaxResults(5);
分组与统计
session.beginTransaction();
Criteria c = session.createCriteria(User.class);
c.setProjection(Projections.sum("id"));
Object obj = c.uniqueResult();
System.out.println(obj);
session.getTransaction()
.commit();Projections对象
方法名称 描述 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - Projections.sum 等于SQL中聚合函数sum Projections.avg 等于SQL中聚合函数avg Projections.count 等于SQL中聚合函数count Projections.distinct 去除重复记录 Projections.max 等于SQL中聚合函数max Projections.min 等于SQL中聚合函数min Projections.groupProperty 对指定的属性进行分组查询
多个统计与分组
session.beginTransaction();
Criteria c = session.createCriteria(User.class);
ProjectionList projectionList = Projections.projectionList();
projectionList.add(Projections.sum("id"));
projectionList.add(Projections.min("id"));
c.setProjection(projectionList);
// 和HQL一样，单列用Object，多列用Object[]
Object[] obj = (Object[]) c.uniqueResult();
System.out.println("sum:" + obj[0]);
System.out.println("min:" + obj[1]);排序
Criteria c = session.createCriteria(User.class);
c.addOrder(Order.desc("id"));三、原生SQL查询：
示例
session.beginTransaction();
String sql = "select id,username,userpwd from t_user";
List list = session.createSQLQuery(sql)
.list();
for (Object item: list)
{
Object[] rows = (Object[]) item;
System.out.println("id:" + rows[0] + "username:" +
rows[1] + "userpwd:" + rows[2]);
}
session.getTransaction()
.commit();addEntity()示例
session.beginTransaction();
String sql = "select id,username,userpwd from t_user";
// addEntity()可以告诉Hibernate你想要封装成对象的类型，然后自动为你封装
SQLQuery query = session.createSQLQuery(sql)
.addEntity(User.class);
List < User > list = query.list();
for (User user: list)
{
System.out.println(user.getUserName());
}
session.getTransaction()
.commit();uniqueResult示例
session.beginTransaction(); String sql = "select id,username,userpwd from t_user where id = 2"; SQLQuery query = session.createSQLQuery(sql) .addEntity(User.class); User user = (User) query.uniqueResult(); System.out.println(user.getUserName()); session.getTransaction() .commit();
hibernate的查询方式就是 HQL、QBC以及使用原生SQL查询这三种，每种查询我们都做出了相关的示例，在实际开发中如果遇到hibernate查询方式我们可以根据实际情况去使用哦!最后大家如果想要了解更多java架构师知识，敬请关注奇Q工具网。
推荐阅读：