Hibernate检索策略学习之--批量加载

最新推荐文章于 2024-05-14 17:32:15 发布

daryl715

最新推荐文章于 2024-05-14 17:32:15 发布

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分类专栏：经验技巧之Hibernate 文章标签： hibernate generator class encoding import table

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本文通过实例讲解了批量加载的概念，展示了如何使用Hibernate配置批量加载参数来减少数据库查询次数，提升应用程序性能。

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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

<?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">

<!--

Mapping file autogenerated by MyEclipse - Hibernate Tools

-->

<hibernate-mapping package="Search.batch.immediately" >

</id>

<one-to-one name="cer"

class="Search.batch.immediately.Certificate"

constrained="true"

lazy="no-proxy"

outer-join="false"

cascade="all">

</one-to-one>

<many-to-one name="team"

column="team_id"

outer-join="false"

class="Search.batch.immediately.Team"></many-to-one>

</class>

</hibernate-mapping>

Certificate.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">

<!--

Mapping file autogenerated by MyEclipse - Hibernate Tools

-->

<hibernate-mapping package="Search.batch.immediately" >

</generator>

</id>

<one-to-one name="stu"

class="Search.batch.immediately.Student"

outer-join="false"

constrained="true">

</one-to-one>

</class>

</hibernate-mapping>

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">

<!--

Mapping file autogenerated by MyEclipse - Hibernate Tools

-->

<hibernate-mapping package="Search.batch.immediately" >

</id>

<set name="students"

lazy="false"

inverse="true"

outer-join="false"

<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=

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=?

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=?

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=?

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">

<!--

Mapping file autogenerated by MyEclipse - Hibernate Tools

-->

<hibernate-mapping package="Search.batch.immediately" >

</id>

<set name="students"

lazy="false"

inverse="true"

outer-join="false"

batch-size="2"

<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 (?, ?)

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 (?, ?)

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=?

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">

<!--

Mapping file autogenerated by MyEclipse - Hibernate Tools

-->

<hibernate-mapping package="Search.batch.immediately" >

</id>

<set name="students"

lazy="true"

inverse="true"

outer-join="false"

batch-size="2"

<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_

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 (?, ?)
team1:2
team2:1

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 (?, ?)
team3:1
team4:1

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=?
team5:1

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