4、Hibernate的查询方式

一、Hibernate的查询方式:OID查询

1、OID检索:Hibernate根据对象的OID(主键)进行检索

1-1、使用get方法

Customer customer = session.get(Customer.class,1L);

1-2、使用load方法

Customer customer = session.load(Customer.class,1L);

 

3、对象导航检索:Hibernate根据一个已经查询到的对象,获得其关联的对象的一种查询方式。

Customer customer = session.get(Customer.class,1L);
Set<LinkMan> linkManSet = customer.getLinkMans();

 

4-1、HQL查询

Hibernate Query Language,Hibernate的查询语言,是一种面向对象的方式的查询语言,语法类似SQL。通过session.createQuery(),用于接收一个HQL进行查询方式。

package com.turtle.test;

import java.util.Arrays;
import java.util.List;

import com.turtle.dao.Customer;
import com.turtle.dao.LinkMan;
import com.turtle.utils.HibernateUtils;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;


/**
 * HQL的查询方式的测试类
 *
 * @author jt
 *
 */
public class Hibernater_01 {

    @Test
    /**
     * 初始化数据
     */
    public void demo1() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 创建一个客户
        Customer customer = new Customer();
        customer.setCust_name("李向文");

        for (int i = 1; i <= 10; i++) {
            LinkMan linkMan = new LinkMan();
            linkMan.setLkm_name("王东" + i);
            linkMan.setCustomer(customer);

            customer.getLinkMans().add(linkMan);

            session.save(linkMan);
        }
        session.save(customer);

        tx.commit();
    }

    @Test
    /**
     * HQL的简单查询
     */
    public void demo2() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        // 简单的查询
        Query query = session.createQuery("from Customer");
        List<Customer> list = query.list();

        // sql中支持*号的写法:select * from cst_customer; 但是在HQL中不支持*号的写法。
        /*
         * Query query = session.createQuery("select * from Customer");// 报错
         * List<Customer> list = query.list();
         */

        for (Customer customer : list) {
            System.out.println(customer);
        }
        tx.commit();
    }

    @Test
    /**
     * 别名查询
     */
    public void demo3() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        // 别名的查询
        /*
         * Query query = session.createQuery("from Customer c"); List<Customer>
         * list = query.list();
         */

        Query query = session.createQuery("select c from Customer c");
        List<Customer> list = query.list();

        for (Customer customer : list) {
            System.out.println(customer);
        }
        tx.commit();
    }

    @Test
    /**
     * 排序查询
     */
    public void demo4() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        // 排序的查询
        // 默认情况
        // List<Customer> list = session.createQuery("from Customer order by
        // cust_id").list();
        // 设置降序排序 升序使用asc 降序使用desc
        List<Customer> list = session.createQuery("from Customer order by cust_id desc").list();

        for (Customer customer : list) {
            System.out.println(customer);
        }
        tx.commit();
    }

    @Test
    /**
     * 条件查询
     */
    public void demo5() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        // 条件的查询
        // 一、按位置绑定:根据参数的位置进行绑定。
        // 一个条件
        /*
         * Query query = session.createQuery("from Customer where cust_name = ?"); 
         * query.setParameter(0, "李兵"); 
         * List<Customer> list = query.list();
         */

        // 多个条件
        /*
         * Query query = session.createQuery(
         * "from Customer where cust_source = ? and cust_name like ?");
         * query.setParameter(0, "小广告"); 
         * query.setParameter(1, "李%");
         * List<Customer> list = query.list();
         */

        // 二、按名称绑定
        Query query = session.createQuery("from Customer where cust_source = :aaa and cust_name like :bbb");
        // 设置参数:
        query.setParameter("aaa", "朋友推荐");
        query.setParameter("bbb", "李%");
        List<Customer> list = query.list();

        for (Customer customer : list) {
            System.out.println(customer);
        }
        tx.commit();
    }

    @Test
    /**
     * 投影查询
     */
    public void demo6() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 投影查询
        // 单个属性
        /*
         * List<Object> list = session.createQuery("select c.cust_name from Customer c").list(); 
         * for (Object object :list) { 
         *      System.out.println(object);
          * }
         */

        // 多个属性:
        /*
         * List<Object[]> list = session.createQuery(
         * "select c.cust_name,c.cust_source from Customer c").list(); for
         * (Object[] objects : list) {
         * System.out.println(Arrays.toString(objects)); }
         */

        // 查询多个属性,但是我想封装到对象中。
        List<Customer> list = session.createQuery("select new Customer(cust_name,cust_source) from Customer").list();
        for (Customer customer : list) {
            System.out.println(customer);
        }
        tx.commit();
    }

    @Test
    /**
     * 分页查询
     */
    public void demo7() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 分页查询
        Query query = session.createQuery("from LinkMan");
        query.setFirstResult(20);
        query.setMaxResults(10);
        List<LinkMan> list = query.list();

        for (LinkMan linkMan : list) {
            System.out.println(linkMan);
        }
        tx.commit();
    }

    @Test
    /**
     * 分组统计查询
     */
    public void demo8() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 聚合函数的使用:count(),max(),min(),avg(),sum()
        Object object = session.createQuery("select count(*) from Customer").uniqueResult();
        System.out.println(object);
        // 分组统计:
        List<Object[]> list = session.createQuery("select cust_source,count(*) from Customer group by cust_source")
                .list();
        for (Object[] objects : list) {
            System.out.println(Arrays.toString(objects));
        }
        tx.commit();
    }

    @Test
    /**
     * HQL的多表查询
     */
    public void demo9() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        // SQL:SELECT * FROM cst_customer c INNER JOIN cst_linkman l ON
        // c.cust_id = l.lkm_cust_id;
        // HQL:内连接 from Customer c inner join c.linkMans
        /*
         * List<Object[]> list = session.createQuery("from Customer c inner join c.linkMans").list(); 
         * for (Object[] objects : list) { 
         *      System.out.println(Arrays.toString(objects)); 
         * }
         */

        // HQL:迫切内连接 其实就在普通的内连接inner join后添加一个关键字fetch. from Customer c inner
        // join fetch c.linkMans
        List<Customer> list = session.createQuery("select distinct c from Customer c inner join fetch c.linkMans")
                .list();// 通知hibernate,将另一个对象的数据封装到该对象中

        for (Customer customer : list) {
            System.out.println(customer);
        }
        tx.commit();
    }

}

 

 

4-2、 HQL的多表查询

  SQL的多表查询

  连接查询

  交叉连接:笛卡尔积

select * from A,B;

  内连接    :inner join (inner 可以省略)

  隐式内连接:

select * from A,B where A.id = B.aid;

  显示内连接:

select * from A inner join B on A.id = B.aid;

  外连接    :

  左外连接:left outer join(outer 可以省略)

select * from A left outer join B on A.id= B.aid;

  右外连接:right outer join(outer 可以省略)

select * from A right outer join B on A.id = B.aid;

  子查询

 

 HQL的多表查询

  连接查询

  交叉连接

  内连接

  显示内连接

  隐式内连接

  迫切内连接

  外连接

  左外连接

  右外连接

  迫切左外连接

 

5、QBC查询:Query By Criteria,条件查询。是一种更加面向对象化的查询的方式。

package com.turtle.test;

import java.util.List;

import com.turtle.dao.Customer;
import com.turtle.dao.LinkMan;
import com.turtle.utils.HibernateUtils;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.criterion.DetachedCriteria;
import org.hibernate.criterion.Order;
import org.hibernate.criterion.Projections;
import org.hibernate.criterion.Restrictions;
import org.junit.Test;


/**
 * QBC的查询
 * @author jt
 *
 */
public class Hibernater_02 {

    @Test
    /**
     * 简单的查询
     */
    public void demo1(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 获得Criteria的对象
        Criteria criteria = session.createCriteria(Customer.class);
        List<Customer> list = criteria.list();

        for (Customer customer : list) {
            System.out.println(customer);
        }
        tx.commit();
    }

    @Test
    /**
     * 排序查询
     */
    public void demo2(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 排序查询
        Criteria criteria = session.createCriteria(Customer.class);
//        criteria.addOrder(Order.asc("cust_id")); // 升序
        criteria.addOrder(Order.desc("cust_id")); // 降序
        List<Customer> list = criteria.list();

        for (Customer customer : list) {
            System.out.println(customer);
        }

        tx.commit();
    }

    @Test
    /**
     * 分页查询
     */
    public void demo3(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 分页查询
        Criteria criteria = session.createCriteria(LinkMan.class);
        criteria.setFirstResult(10);
        criteria.setMaxResults(10);
        List<LinkMan> list = criteria.list();

        for (LinkMan linkMan : list) {
            System.out.println(linkMan);
        }
        tx.commit();
    }

    @Test
    /**
     * 条件查询
     */
    public void demo4(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 条件查询
        Criteria criteria = session.createCriteria(Customer.class);
        // 设置条件:
        /**
         * =   eq
         * >   gt
         * >=  ge
         * <   lt
         * <=  le
         * <>  ne
         * like
         * in
         * and
         * or
         */
        criteria.add(Restrictions.eq("cust_source", "小广告"));
//        criteria.add(Restrictions.or(Restrictions.like("cust_name", "李%")));
        criteria.add(Restrictions.like("cust_name", "李%"));
        List<Customer> list = criteria.list();
        for (Customer customer : list) {
            System.out.println(customer);
        }
        tx.commit();
    }

    @Test
    /**
     * 统计查询
     */
    public void demo5(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        Criteria criteria = session.createCriteria(Customer.class);
        /**
         * add                :普通的条件。where后面条件
         * addOrder            :排序
         * setProjection    :聚合函数 和 group by having
         */
        criteria.setProjection(Projections.rowCount());
        Long num = (Long) criteria.uniqueResult();
        System.out.println(num);
        tx.commit();
    }

    @Test
    /**
     * 离线条件查询
     */
    public void demo6(){
        DetachedCriteria detachedCriteria = DetachedCriteria.forClass(Customer.class);
        detachedCriteria.add(Restrictions.like("cust_name", "李%"));

        Session session = HibernateUtils.getCurrentSession();
        Transaction transaction = session.beginTransaction();

        Criteria criteria = detachedCriteria.getExecutableCriteria(session);
        List<Customer> list = criteria.list();
        for (Customer customer : list) {
            System.out.println(customer);
        }
        transaction.commit();
    }
}

 

                                                                   

 

 

 

6、SQL查询:通过使用sql语句进行查询

package com.turtle.test;

import java.util.Arrays;
import java.util.List;

import com.turtle.dao.Customer;
import com.turtle.utils.HibernateUtils;
import org.hibernate.SQLQuery;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

/**
 * SQL查询
 * @author jt
 *
 */
public class Hibernate_03 {

    @Test
    public void demo1(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        /*SQLQuery sqlQuery = session.createSQLQuery("select * from cst_customer");
        List<Object[]> list = sqlQuery.list();
        for (Object[] objects : list) {
            System.out.println(Arrays.toString(objects));
        }*/

        SQLQuery sqlQuery = session.createSQLQuery("select * from cst_customer");
        // 这样就可以操作对应的对象了
        sqlQuery.addEntity(Customer.class);
        List<Customer> list = sqlQuery.list();
        for (Customer customer : list) {
            System.out.println(customer);
        }
        tx.commit();
    }
}

 

 

二、 Hibernate的抓取策略(优化)

1、   延迟加载

什么是延迟加载

延迟加载:lazy(懒加载)。执行到该行代码的时候,不会发送语句去进行查询,在真正使用这个对象的属性的时候才会发送SQL语句进行查询。

延迟加载的分类

  类级别的延迟加载

  指的是通过load方法查询某个对象的时候,是否采用延迟。session.load(Customer.class,1l);

  类级别延迟加载通过<class>上的lazy进行配置,如果让lazy失效

  将lazy设置为false

  将持久化类使用final修饰

  Hibernate. Initialize()

  关联级别的延迟加载

  指的是在查询到某个对象的时候,查询其关联的对象的时候,是否采用延迟加载。

Customer customer = session.get(Customer.class,1l);

customer.getLinkMans();----通过客户获得联系人的时候,联系人对象是否采用了延迟加载,称为是关联级别的延迟。

 抓取策略往往会和关联级别的延迟加载一起使用,优化语句。

package com.turtle.test2;

import com.turtle.dao.Customer;
import com.turtle.utils.HibernateUtils;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;


/**
 * Hibernate的延迟加载
 * @author jt
 *
 */
public class Hibernate_01 {

    @Test
    /**
     * 类级别的延迟加载
     * * 在<class>的标签上配置的lazy
     */
    public void demo1(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        Customer customer = session.load(Customer.class, 1L);
        Hibernate.initialize(customer);
        System.out.println(customer);

        tx.commit();
    }
}

 

2、抓取策略

 抓取策略的概述

 通过一个对象抓取到关联对象需要发送SQL语句,SQL语句如何发送,发送成什么样格式通过策略进行配置。

  通过<set>或者<many-to-one>上通过fetch属性进行设置

  fetch和这些标签上的lazy如何设置优化发送的SQL语句

2-1  <set>上的fetch和lazy

  fetch:抓取策略,控制SQL语句格式

    select                        :默认值,发送普通的select语句,查询关联对象

    join                           :发送一条迫切左外连接查询关联对象

    subselect                 :发送一条子查询查询其关联对象

  lazy                          :延迟加载,控制查询关联对象的时候是否采用延迟

    true                        :默认值,查询关联对象的时候,采用延迟加载

    false                       :查询关联对象的时候,不采用延迟加载

    extra                     :及其懒惰。

在实际开发中,一般都采用默认值。如果有特殊的需求,可能需要配置join

package com.turtle.test2;

import java.util.List;

import com.turtle.dao.Customer;
import com.turtle.dao.LinkMan;
import com.turtle.utils.HibernateUtils;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;


/**
 * 在<set>上的fetch和lazy
 * @author jt
 *
 */
public class Hibernate_02 {

    @Test
    /**
     * 默认情况:
     */
    public void demo1(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 查询1号客户
        Customer customer = session.get(Customer.class, 1L);// 发送一条查询客户的SQL
        System.out.println(customer.getCust_name());
        // 查看1号客户的每个联系人的信息
        for (LinkMan linkMan : customer.getLinkMans()) {// 发送一条根据客户ID查询联系人的SQL
            System.out.println(linkMan.getLkm_name());
        }
        tx.commit();
    }

    @Test
    /**
     * 设置fetch="select" lazy="true"
     */
    public void demo2(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 查询1号客户
        Customer customer = session.get(Customer.class, 1l);// 发送一条查询客户的SQL
        System.out.println(customer.getCust_name());
        // 查看1号客户的每个联系人的信息
        for (LinkMan linkMan : customer.getLinkMans()) {// 发送一条根据客户ID查询联系人的SQL
            System.out.println(linkMan.getLkm_name());
        }
        tx.commit();
    }

    @Test
    /**
     * 设置    fetch="select" lazy="false"
     */
    public void demo3(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 查询1号客户
        Customer customer = session.get(Customer.class, 1l);// 发送两条SQL语句:查询客户的名称,查询客户关联联系人
        System.out.println(customer.getCust_name());
        /*// 查看1号客户的每个联系人的信息
        for (LinkMan linkMan : customer.getLinkMans()) {//
            System.out.println(linkMan.getLkm_name());
        }*/

        System.out.println(customer.getLinkMans().size());
        tx.commit();
    }

    @Test
    /**
     * 设置fetch="select" lazy="extra"
     */
    public void demo4(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 查询1号客户
        Customer customer = session.get(Customer.class, 1l);// 发送一条查询1号客户的SQL语句
        System.out.println(customer.getCust_name());

        System.out.println(customer.getLinkMans().size());// 发送一条select count() from ...;
        tx.commit();
    }

    @Test
    /**
     * 设置fetch="join" lazy=失效
     */
    public void demo5(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        // 查询1号客户
        Customer customer = session.get(Customer.class, 1l);// 发送一条迫切左外连接查询记录
        System.out.println(customer.getCust_name());

        System.out.println(customer.getLinkMans().size());// 不发送
        tx.commit();
    }

    @SuppressWarnings("unchecked")
    @Test
    /**
     * 设置fetch="subselect" lazy="true"
     */
    public void demo6(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        List<Customer> list = session.createQuery("from Customer").list();// 发送查询所有客户的SQL
        for (Customer customer : list) {
            System.out.println(customer.getCust_name());
            System.out.println(customer.getLinkMans().size());// 发送一条子查询
        }

        tx.commit();
    }

    @SuppressWarnings("unchecked")
    @Test
    /**
     * 设置fetch="subselect" lazy="false"
     */
    public void demo7(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        List<Customer> list = session.createQuery("from Customer").list();// 发送查询所有客户的SQL,发送一条子查询
        for (Customer customer : list) {
            System.out.println(customer.getCust_name());
            System.out.println(customer.getLinkMans().size());//
        }

        tx.commit();
    }
}

 

 2-1<many-to-one>上的fetch和lazy

  fetch :抓取策略,控制SQL语句格式。

    select       :默认值,发送普通的select语句,查询关联对象。

    join           :发送一条迫切左外连接。

 lazy   :延迟加载,控制查询关联对象的时候是否采用延迟。

    proxy       :默认值,proxy具体的取值,取决于另一端的<class>上的lazy的值。

    false         :查询关联对象,不采用延迟。

   no-proxy :(不会使用)

在实际开发中,一般都采用默认值。如果有特殊的需求,可能需要配置join

package com.turtle.test2;

import com.turtle.dao.LinkMan;
import com.turtle.utils.HibernateUtils;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;


/**
 * many-to-one上的fetch和lazy测试
 * @author jt
 *
 */
public class Hibernate_03 {

    @Test
    /**
     * 默认值
     */
    public void demo1(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        LinkMan linkMan = session.get(LinkMan.class, 1l);// 发送一条查询联系人语句
        System.out.println(linkMan.getLkm_name());
        System.out.println(linkMan.getCustomer().getCust_name());// 发送一条select语句查询联系人所关联的客户

        tx.commit();
    }

    @Test
    /**
     * fetch="select" lazy="proxy"
     */
    public void demo2(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        LinkMan linkMan = session.get(LinkMan.class, 1l);// 发送一条查询联系人语句
        System.out.println(linkMan.getLkm_name());
        System.out.println(linkMan.getCustomer().getCust_name());// 发送一条select语句查询联系人所关联的客户

        tx.commit();
    }

    @Test
    /**
     * fetch="select" lazy="false"
     */
    public void demo3(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        LinkMan linkMan = session.get(LinkMan.class, 1l);// 发送一条查询联系人语句,发送一条select语句查询联系人所关联的客户
        System.out.println(linkMan.getLkm_name());
        System.out.println(linkMan.getCustomer().getCust_name());//

        tx.commit();
    }

    @Test
    /**
     * fetch="join" lazy=失效
     */
    public void demo4(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        LinkMan linkMan = session.get(LinkMan.class, 1l);// 发送一条迫切左外连接查询联系人所关联的客户。
        System.out.println(linkMan.getLkm_name());
        System.out.println(linkMan.getCustomer().getCust_name());//

        tx.commit();
    }
}

 

3、批量抓取,一批关联对象一起抓取,batch-size

package com.turtle.test2;

import java.util.List;

import com.turtle.dao.Customer;
import com.turtle.dao.LinkMan;
import com.turtle.utils.HibernateUtils;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;


/**
 * 批量抓取
 * @author jt
 *
 */
public class Hibernate_04 {

    @SuppressWarnings("unchecked")
    @Test
    /**
     * 获取客户的时候,批量抓取联系人
     * 在Customer.hbm.xml中set上配置batch-size
     */
    public void demo1(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        List<Customer> list = session.createQuery("from Customer").list();
        for (Customer customer : list) {
            System.out.println(customer.getCust_name());
            for (LinkMan linkMan : customer.getLinkMans()) {
                System.out.println(linkMan.getLkm_name());
            }
        }
        tx.commit();
    }

    @SuppressWarnings("unchecked")
    @Test
    /**
     * 获取联系人的时候,批量抓取客户
     * * 在Customer.hbm.xml中<class>上配置
     */
    public void demo2(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();

        List<LinkMan> list = session.createQuery("from LinkMan").list();
        for (LinkMan linkMan : list) {
            System.out.println(linkMan.getLkm_name());
            System.out.println(linkMan.getCustomer().getCust_name());
        }
        tx.commit();
    }
}

 

 

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转载自www.cnblogs.com/zhh19981104/p/11830878.html