6.0、Hibernate-HQL

HQL 全称（Hibernate Query Language），是 Hibernate 框架提供的一种查询机制，他和 SQL 类似，不同的是 HQL 是面向对象的查询语句，让开发者能够以面向对象的思想来编写查询语句，对 Java 编程是一种友好的方式；HQL 不能直接参与数据库的交互，中间层语言 -> Java ---> HQL ---> Hibernate ---> SQL ---> DB；H

澜色海湾

885人浏览 · 2022-12-28 12:31:02

澜色海湾 · 2022-12-28 12:31:02 发布

6.0、Hibernate-HQL

HQL 全称（Hibernate Query Language），是 Hibernate 框架提供的一种查询机制，他和 SQL 类似，不同的是 HQL 是面向对象的查询语句，让开发者能够以面向对象的思想来编写查询语句，对 Java 编程是一种友好的方式；

HQL 不能直接参与数据库的交互，中间层语言 -> Java ---> HQL ---> Hibernate ---> SQL ---> DB；

HQL 只能完成查询、修改、删除，新增是无法操作的；

1、查询对象

查询表中所有数据，自动完成对象的封装，返回 List 集合；

HQL 进行查询，from 关键字后面不能写表名，必须写对应的实体类名；

参考代码，如下所示->

import com.hkl.pojo.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;

import java.util.List;

public class Test9 {
    public static void main(String[] args) {
        //        创建configuration
        Configuration configuration = new Configuration().configure();
//        获取sessionFactory
        SessionFactory sessionFactory = configuration.buildSessionFactory();
//        获取Session
        Session session = sessionFactory.openSession();

        String hql  = "from People";
        Query query = session.createQuery(hql);
        List<People> list = query.list();
        for(People people:list) {
            System.out.println(people);
        }

        session.close();
    }
}

2、分页查询

HQL 分页查询可以通过调用 query 的方法来完成；

1、setFirstResult() -设置起始下标；

2、setMaxResult() -设置截取长度；

参考代码，如下所示->

import com.hkl.pojo.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;

import java.util.List;

public class Test9 {
    public static void main(String[] args) {
        //        创建configuration
        Configuration configuration = new Configuration().configure();
//        获取sessionFactory
        SessionFactory sessionFactory = configuration.buildSessionFactory();
//        获取Session
        Session session = sessionFactory.openSession();

        String hql = "from People";
        Query query = session.createQuery(hql);
        query.setFirstResult(1);
        query.setMaxResults(3);
        List<People> list = query.list();
        for(People people:list) {
            System.out.println(people);
        }
        session.close();
    }
}

3、where 条件查询

HQL 直接追加 where 关键字作为查询条件，与 SQL 没有区别；

参考代码，如下所示 ->

import com.hkl.pojo.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;

import java.util.List;

public class Test9 {
    public static void main(String[] args) {
        //        创建configuration
        Configuration configuration = new Configuration().configure();
//        获取sessionFactory
        SessionFactory sessionFactory = configuration.buildSessionFactory();
//        获取Session
        Session session = sessionFactory.openSession();

        String hql = "from People where id = 6";
        Query query = session.createQuery(hql);
        People people = (People) query.list().get(0);
        System.out.println(people);
        
        session.close();
    }
}

query.list() 返回一个集合，此时集合中只有一个对象，通过下标 0 取出该对象；

4、模糊查询

查询名称包含 " 澜 " 的所有记录；

参考代码，如下所示 ->

import com.hkl.pojo.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;

import java.util.List;

public class Test9 {
    public static void main(String[] args) {
        //        创建configuration
        Configuration configuration = new Configuration().configure();
//        获取sessionFactory
        SessionFactory sessionFactory = configuration.buildSessionFactory();
//        获取Session
        Session session = sessionFactory.openSession();

        String hql = "from People where name like '%澜%'";
        Query query = session.createQuery(hql);
        List<People> list = query.list();
        for(People people:list) {
            System.out.println(people);
        }

        session.close();
    }
}

5、order by

按照 id 进行排序；

参考代码，如下所示 ->

import com.hkl.pojo.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;

import java.util.List;

public class Test9 {
    public static void main(String[] args) {
        //        创建configuration
        Configuration configuration = new Configuration().configure();
//        获取sessionFactory
        SessionFactory sessionFactory = configuration.buildSessionFactory();
//        获取Session
        Session session = sessionFactory.openSession();

        String hql = "from People order by id desc";
        Query query = session.createQuery(hql);
        List<People> list = query.list();
        for(People people:list) {
            System.out.println(people);
        }

        session.close();
    }
}

asc 是升序排列，desc 是降序排列；

6、查询实体对象的属性

参考代码，如下所示 ->

import com.hkl.pojo.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;

import java.util.List;

public class Test9 {
    public static void main(String[] args) {
        //        创建configuration
        Configuration configuration = new Configuration().configure();
//        获取sessionFactory
        SessionFactory sessionFactory = configuration.buildSessionFactory();
//        获取Session
        Session session = sessionFactory.openSession();

        String hql = "select name from People where id = 6";
        Query query = session.createQuery(hql);
        List<People> list = query.list();
        System.out.println(people);

        session.close();
    }
}

7、占位符

参考代码，如下所示 ->

import com.hkl.pojo.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;

import java.util.List;

public class Test9 {
    public static void main(String[] args) {
        //        创建configuration
        Configuration configuration = new Configuration().configure();
//        获取sessionFactory
        SessionFactory sessionFactory = configuration.buildSessionFactory();
//        获取Session
        Session session = sessionFactory.openSession();

        String hql = "from People where name = :name";
        Query query = session.createQuery(hql);
        query.setString("name","小澜");
        List<People> list = query.list();
        for(People people:list) {
            System.out.println(people);
        }

        session.close();
    }
}

8、级联查询

参考代码，如下所示 ->

import com.hkl.pojo.Customer;
import com.hkl.pojo.Order;
import com.hkl.pojo.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;

import java.util.List;

public class Test9 {
    public static void main(String[] args) {
        //        创建configuration
        Configuration configuration = new Configuration().configure();
//        获取sessionFactory
        SessionFactory sessionFactory = configuration.buildSessionFactory();
//        获取Session
        Session session = sessionFactory.openSession();

        String hql1 = "from Customer where name = :name";
        Query query1 = session.createQuery(hql1);
        query1.setString("name","小澜");
        Customer customer = (Customer) query1.uniqueResult();
        String hql2 = "from Order where customer = :customer";
        Query query2 = session.createQuery(hql2);
        query2.setString("customer",customer);
        List<Order> list = query2.list();
        for(Order orders:list) {
            System.out.println(orders);
        }

        session.close();
    }
}