Hibernate检索策略学习之--批量加载

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hibernate

Hibernate Myeclipse SQL XML .net

所谓批量加载，即把原本要发送的SQL分批统一发送，比如说原本要发送100条SQL,如果设置batch-size=3,则只需要发送100/3+1=34条，可以提高效率

批量加载分为延迟加载和立即加载，先说立即加在

首先建立测试数据库

CREATE TABLE certificate (
id varchar(100) NOT NULL default '',
description varchar(100) default '',
PRIMARY KEY (id)
);

CREATE TABLE student (
team_id varchar(100) default '',
id varchar(100) NOT NULL default '',
name varchar(20) default '',
cardId varchar(20) NOT NULL default '',
age int(11) default '0',
PRIMARY KEY (id)
);

CREATE TABLE team (
id varchar(100) NOT NULL default '',
teamName varchar(100) default '',
PRIMARY KEY (id)
);

INSERT INTO student VALUES
('5','1','spark','200211332',13),
('4','2','jerry','200233332',23),
('3','3','adidas','200231332',33),
('2','4','zhouxingchi','200231132',43),
('1','5','tomclus','200512345',53),
('1','6','tom','200511345',63);

INSERT INTO team VALUES
('5','team5'),
('4','team4'),
('3','team3'),
('2','team2'),
('1','team1');

INSERT INTO certificate VALUES
('1','card1'),
('2','card2'),
('3','card3'),
('4','card4'),
('5','card5'),
('6','card6');

建立POJO对象

package Search.immediately;

public class Certificate ............{
    private String id;
    private String description;
    private Student stu;

    public Student getStu() ............{
        return stu;
    }

    public void setStu(Student stu) ............{
        this.stu = stu;
    }

    public String getDescription() ............{
        return description;
    }

    public void setDescription(String description) ............{
        this.description = description;
    }

    public String getId() ............{
        return id;
    }

    public void setId(String id) ............{
        this.id = id;
    }
}

package Search.immediately;

import java.util.HashSet;
import java.util.Set;

public class Team ............{
    private String id;
    private Set students=new HashSet();
    private String teamName;
    private Set tests;

    public Set getTests() ............{
        return tests;
    }

    public void setTests(Set tests) ............{
        this.tests = tests;
    }

    public String getId() ............{
        return id;
    }

    public void setId(String id) ............{
        this.id = id;
    }

    public String getTeamName() ............{
        return teamName;
    }

    public void setTeamName(String name) ............{
        this.teamName = name;
    }

    public Set getStudents() ............{
        return students;
    }

    public void setStudents(Set students) ............{
        this.students = students;
    }
}

package Search.immediately;

public class Certificate ............{
    private String id;
    private String description;
    private Student stu;

    public Student getStu() ............{
        return stu;
    }

    public void setStu(Student stu) ............{
        this.stu = stu;
    }

    public String getDescription() ............{
        return description;
    }

    public void setDescription(String description) ............{
        this.description = description;
    }

    public String getId() ............{
        return id;
    }

    public void setId(String id) ............{
        this.id = id;
    }
}

HBM文件

student.hbm.xml

Certificate.hbm.xml

Team.hbm.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="Search.batch.immediately" >
    <class name="Team" table="team" lazy="false">
       <id name="id" column="id">
         <generator class="uuid.hex"></generator>
       </id>
       <property name="teamName" column="teamName"></property>
        
       <set name="students"
            lazy="false"
            inverse="true"
            outer-join="false"
           >
         <key column="team_id"></key>
         <one-to-many class="Search.batch.immediately.Student"/>
       </set>
      </class>
</hibernate-mapping>

测试代码：

package Search.batch.immediately;

import java.io.File;
import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class Test ...{

    public static void main(String[] args) ...{
        Team team=null;
        String filePath=System.getProperty("user.dir")+File.separator+"src/Search/batch/immediately"+File.separator+"hibernate.cfg.xml";
        File file=new File(filePath);
        SessionFactory sessionFactory=new Configuration().configure(file).buildSessionFactory();
        Session session=sessionFactory.openSession();
        Query query=session.createQuery("from Team t");
        List resultList=query.list();

}

运行，结果如下：

Hibernate: select team0_.id as id2_, team0_.teamName as teamName2_ from team team0_

Hibernate: select students0_.team_id as team5_1_, students0_.id as id1_, students0_.id as id1_0_, students0_.cardId as cardId1_0_, students0_.name as name1_0_, students0_.age as age1_0_, students0_.team_id as team5_1_0_ from student students0_ where students0_.team_id=

有5条查询student的SQL(本身有6个学生，但有两个学生属于一个team)
可以看到，这是典型的立即加在，取得team对象后，把team所包含的student取出，如果有100个学生，则会执行100个SQL,这是很没有效率的

我们修改Team的hbm文件，为其配置批量加载student的配置（1对多在set标签上配置，多对1在class标签上配置）

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="Search.batch.immediately" >
    <class name="Team" table="team" lazy="false">
       <id name="id" column="id">
         <generator class="uuid.hex"></generator>
       </id>
       <property name="teamName" column="teamName"></property>
        
       <set name="students"
            lazy="false"
            inverse="true"
            outer-join="false"
            batch-size="2"
           >
         <key column="team_id"></key>
         <one-to-many class="Search.batch.immediately.Student"/>
       </set>
      </class>
</hibernate-mapping>

再次运行测试程序，结果如下：

Hibernate: select team0_.id as id2_, team0_.teamName as teamName2_ from team team0_

Hibernate: select students0_.team_id as team5_1_, students0_.id as id1_, students0_.id as id1_0_,
students0_.cardId as cardId1_0_, students0_.name as name1_0_, students0_.age as age1_0_, students0_.team_id as team5_1_0_ from student students0_ where students0_.team_id in (?, ?)

可以看到，查询student只用了3条SQL(5/batch-size+1=3),

如果team对student是延迟加载的，会使什么效果呢，会是这样，我们加载team1时候，由于batch-size=2,所以加载team1就同时批量加载了team2,同理，加载team3时候也就加载了team4，最后再加载team5, 而这些数据都已经在hibernate session的缓存中了

修改team.hbm.xml 配置好lazy="true"

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="Search.batch.immediately" >
    <class name="Team" table="team" lazy="false">
       <id name="id" column="id">
         <generator class="uuid.hex"></generator>
       </id>
       <property name="teamName" column="teamName"></property>
        
       <set name="students"
            lazy="true"
            inverse="true"
            outer-join="false"
            batch-size="2"
           >
         <key column="team_id"></key>
         <one-to-many class="Search.batch.immediately.Student"/>
       </set>
      </class>
</hibernate-mapping>

运行测试程序，结果如下：

Hibernate: select team0_.id as id2_, team0_.teamName as teamName2_ from team team0_

其中可以砍到team2和team4的数据是批量加载来的，已经保存在缓存中，所以读取其students集合对象是，虽然是延迟加载，但不再会去发送SQ查询，而是再缓冲中查询

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实体对象的三个状态 | Hibernate inner join fetch,left join fet

2010-11-08 14:57
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