Hibernate实战——@Formula注解

妖狐艹你老母 2021-07-24 20:10 511阅读 0赞

**一 配置文件**

<?xml version="1.0" encoding="GBK"?>
    <!DOCTYPE hibernate-configuration PUBLIC
         "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
         "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
    <hibernate-configuration>
         <session-factory>
               
               <property  name="connection.driver_class">com.mysql.jdbc.Driver</property>
               
               <property  name="connection.url">jdbc:mysql://localhost/hibernate</property>
               
               <property name="connection.username">root</property>
               
               <property name="connection.password">32147</property>
               
               <property  name="hibernate.c3p0.max_size">20</property>
               
               <property name="hibernate.c3p0.min_size">1</property>
               
               <property  name="hibernate.c3p0.timeout">5000</property>
               
               <property  name="hibernate.c3p0.max_statements">100</property>
               <property  name="hibernate.c3p0.idle_test_period">3000</property>
               <property  name="hibernate.c3p0.acquire_increment">2</property>
               <property  name="hibernate.c3p0.validate">true</property>
               
               <property  name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
               
               <property  name="hbm2ddl.auto">update</property>
               
               <property name="show_sql">true</property>
               
               <property name="hibernate.format_sql">true</property>
               
               <mapping class="org.crazyit.app.domain.News"/>
         </session-factory>
    </hibernate-configuration>

**二 PO**

package org.crazyit.app.domain;
    
    import javax.persistence.*;
    import org.hibernate.annotations.Formula;
    
    @Entity
    @Table(name="news_inf")
    public class News
    {
        // 消息类的标识属性
        @Id
        @GeneratedValue(strategy=GenerationType.IDENTITY)
        private Integer id;
        // 消息标题
        private String title;
        // 消息内容
        private String content;
        // 消息全部内容，由系统根据公式生成
        @Formula("(select concat(nt.title,nt.content)"
            + "from news_inf nt where nt.id= id)")
        private String fullContent;
    
        // id的setter和getter方法
        public void setId(Integer id)
        {
            this.id = id;
        }
        public Integer getId()
        {
            return this.id;
        }
    
        // title的setter和getter方法
        public void setTitle(String title)
        {
            this.title = title;
        }
        public String getTitle()
        {
            return this.title;
        }
    
        // content的setter和getter方法
        public void setContent(String content)
        {
            this.content = content;
        }
        public String getContent()
        {
            return this.content;
        }
    
        // fullContent的setter和getter方法
        public void setFullContent(String fullContent)
        {
            this.fullContent = fullContent;
        }
        public String getFullContent()
        {
            return this.fullContent;
        }
    }

**三 测试**

package lee;
    
    import org.hibernate.*;
    import org.hibernate.cfg.*;
    import org.hibernate.service.*;
    import org.hibernate.boot.registry.*;
    import org.crazyit.app.domain.*;
    
    public class NewsManager
    {
        public static void main(String[] args)
            throws Exception
        {
            // 实例化Configuration，
            Configuration conf = new Configuration()
            // 不带参数的configure()方法默认加载hibernate.cfg.xml文件，
            // 如果传入abc.xml作为参数，则不再加载hibernate.cfg.xml，改为加载abc.xml
                .configure();
            ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
                .applySettings(conf.getProperties()).build();
            // 以Configuration实例创建SessionFactory实例
            SessionFactory sf = conf.buildSessionFactory(serviceRegistry);
            // 创建Session
            Session sess = sf.openSession();
            // 开始事务
            Transaction tx = sess.beginTransaction();
    //        // 创建消息对象
    //        News n = new News();
    //        // 设置消息标题和消息内容
    //        n.setTitle("疯狂Java联盟成立了");
    //        n.setContent("疯狂Java联盟成立了，"
    //            + "网站地址http://www.crazyit.org");
    //        // 保存消息
    //        sess.save(n);
            News n = (News)sess.get(News.class , 1);
            // 输出fullContent值
            System.out.println(n.getFullContent());
            // 提交事务
            tx.commit();
            // 关闭Session
            sess.close();
            sf.close();
        }
    }

**四 测试结果**

1 首先生成数据

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70][]

2 查询数据

Hibernate:
        select
            news0_.id as id1_0_0_,
            news0_.content as content2_0_0_,
            news0_.title as title3_0_0_,
            (select
                concat(nt.title,
                nt.content)
            from
                news_inf nt
            where
                nt.id= news0_.id) as formula0_0_
        from
            news_inf news0_
        where
            news0_.id=?
    疯狂Java联盟成立了疯狂Java联盟成立了，网站地址http://www.crazyit.org

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