Hibernate检索策略学习之--批量加载
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
CREATETABLEcertificate(
idvarchar(100)NOTNULLdefault'',
descriptionvarchar(100)default'',
PRIMARYKEY(id)
);
CREATETABLEstudent(
team_idvarchar(100)default'',
idvarchar(100)NOTNULLdefault'',
namevarchar(20)default'',
cardIdvarchar(20)NOTNULLdefault'',
ageint(11)default'0',
PRIMARYKEY(id)
);
CREATETABLEteam(
idvarchar(100)NOTNULLdefault'',
teamNamevarchar(100)default'',
PRIMARYKEY(id)
);
INSERTINTOstudentVALUES
('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);
INSERTINTOteamVALUES
('5','team5'),
('4','team4'),
('3','team3'),
('2','team2'),
('1','team1');
INSERTINTOcertificateVALUES
('1','card1'),
('2','card2'),
('3','card3'),
('4','card4'),
('5','card5'),
('6','card6');
建立POJO对象
packageSearch.immediately;
publicclassCertificate............{
privateStringid;
privateStringdescription;
privateStudentstu;
publicStudentgetStu()............{
returnstu;
}
publicvoidsetStu(Studentstu)............{
this.stu=stu;
}
publicStringgetDescription()............{
returndescription;
}
publicvoidsetDescription(Stringdescription)............{
this.description=description;
}
publicStringgetId()............{
returnid;
}
publicvoidsetId(Stringid)............{
this.id=id;
}
}
packageSearch.immediately;
importjava.util.HashSet;
importjava.util.Set;
publicclassTeam............{
privateStringid;
privateSetstudents=newHashSet();
privateStringteamName;
privateSettests;
publicSetgetTests()............{
returntests;
}
publicvoidsetTests(Settests)............{
this.tests=tests;
}
publicStringgetId()............{
returnid;
}
publicvoidsetId(Stringid)............{
this.id=id;
}
publicStringgetTeamName()............{
returnteamName;
}
publicvoidsetTeamName(Stringname)............{
this.teamName=name;
}
publicSetgetStudents()............{
returnstudents;
}
publicvoidsetStudents(Setstudents)............{
this.students=students;
}
}
packageSearch.immediately;
publicclassCertificate............{
privateStringid;
privateStringdescription;
privateStudentstu;
publicStudentgetStu()............{
returnstu;
}
publicvoidsetStu(Studentstu)............{
this.stu=stu;
}
publicStringgetDescription()............{
returndescription;
}
publicvoidsetDescription(Stringdescription)............{
this.description=description;
}
publicStringgetId()............{
returnid;
}
publicvoidsetId(Stringid)............{
this.id=id;
}
}
HBM文件
student.hbm.xml
<?xmlversion="1.0"encoding="utf-8"?>
<!DOCTYPEhibernate-mappingPUBLIC"-//Hibernate/HibernateMappingDTD3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!--
MappingfileautogeneratedbyMyEclipse-HibernateTools
-->
<hibernate-mappingpackage="Search.batch.immediately">
<classname="Student"table="student"lazy="false">
<idname="id"column="id"unsaved-value="null">
<generatorclass="uuid.hex"></generator>
</id>
<propertyname="cardId"column="cardId"></property>
<propertyname="name"column="name"></property>
<propertyname="age"column="age"></property>
<!--为了设置student-certificate的延迟1对1,设置class的lazy="no-proxy"-->
<one-to-onename="cer"
class="Search.batch.immediately.Certificate"
constrained="true"
lazy="no-proxy"
outer-join="false"
cascade="all">
</one-to-one>
<many-to-onename="team"
column="team_id"
outer-join="false"
class="Search.batch.immediately.Team"></many-to-one>
</class>
</hibernate-mapping>
Certificate.hbm.xml
<?xmlversion="1.0"encoding="utf-8"?>
<!DOCTYPEhibernate-mappingPUBLIC"-//Hibernate/HibernateMappingDTD3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!--
MappingfileautogeneratedbyMyEclipse-HibernateTools
-->
<hibernate-mappingpackage="Search.batch.immediately">
<!--为了设置student-certificate的延迟1对1,设置class的lazy="true"-->
<classname="Certificate"table="certificate"lazy="true">
<idname="id"column="id">
<generatorclass="foreign">
<paramname="property">stu</param>
</generator>
</id>
<propertyname="description"column="description"></property>
<one-to-onename="stu"
class="Search.batch.immediately.Student"
outer-join="false"
constrained="true">
</one-to-one>
</class>
</hibernate-mapping>
Team.hbm.xml
<?xmlversion="1.0"encoding="utf-8"?>
<!DOCTYPEhibernate-mappingPUBLIC"-//Hibernate/HibernateMappingDTD3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!--
MappingfileautogeneratedbyMyEclipse-HibernateTools
-->
<hibernate-mappingpackage="Search.batch.immediately">
<classname="Team"table="team"lazy="false">
<idname="id"column="id">
<generatorclass="uuid.hex"></generator>
</id>
<propertyname="teamName"column="teamName"></property>
<!--需要批量加载,设置batch-size="2"-->
<setname="students"
lazy="false"
inverse="true"
outer-join="false"
>
<keycolumn="team_id"></key>
<one-to-manyclass="Search.batch.immediately.Student"/>
</set>
</class>
</hibernate-mapping>
测试代码:
packageSearch.batch.immediately;
importjava.io.File;
importjava.util.List;
importorg.hibernate.Query;
importorg.hibernate.Session;
importorg.hibernate.SessionFactory;
importorg.hibernate.cfg.Configuration;
publicclassTest...{
publicstaticvoidmain(String[]args)...{
Teamteam=null;
StringfilePath=System.getProperty("user.dir")+File.separator+"src/Search/batch/immediately"+File.separator+"hibernate.cfg.xml";
Filefile=newFile(filePath);
SessionFactorysessionFactory=newConfiguration().configure(file).buildSessionFactory();
Sessionsession=sessionFactory.openSession();
Queryquery=session.createQuery("fromTeamt");
ListresultList=query.list();
}
运行,结果如下:
Hibernate:selectteam0_.idasid2_,team0_.teamNameasteamName2_fromteamteam0_
Hibernate:selectstudents0_.team_idasteam5_1_,students0_.idasid1_,students0_.idasid1_0_,students0_.cardIdascardId1_0_,students0_.nameasname1_0_,students0_.ageasage1_0_,students0_.team_idasteam5_1_0_fromstudentstudents0_wherestudents0_.team_id=
Hibernate:selectstudents0_.team_idasteam5_1_,students0_.idasid1_,students0_.idasid1_0_,students0_.cardIdascardId1_0_,students0_.nameasname1_0_,students0_.ageasage1_0_,students0_.team_idasteam5_1_0_fromstudentstudents0_wherestudents0_.team_id=?
Hibernate:selectstudents0_.team_idasteam5_1_,students0_.idasid1_,students0_.idasid1_0_,students0_.cardIdascardId1_0_,students0_.nameasname1_0_,students0_.ageasage1_0_,students0_.team_idasteam5_1_0_fromstudentstudents0_wherestudents0_.team_id=?
Hibernate:selectstudents0_.team_idasteam5_1_,students0_.idasid1_,students0_.idasid1_0_,students0_.cardIdascardId1_0_,students0_.nameasname1_0_,students0_.ageasage1_0_,students0_.team_idasteam5_1_0_fromstudentstudents0_wherestudents0_.team_id=?
Hibernate:selectstudents0_.team_idasteam5_1_,students0_.idasid1_,students0_.idasid1_0_,students0_.cardIdascardId1_0_,students0_.nameasname1_0_,students0_.ageasage1_0_,students0_.team_idasteam5_1_0_fromstudentstudents0_wherestudents0_.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)
<?xmlversion="1.0"encoding="utf-8"?>
<!DOCTYPEhibernate-mappingPUBLIC"-//Hibernate/HibernateMappingDTD3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!--
MappingfileautogeneratedbyMyEclipse-HibernateTools
-->
<hibernate-mappingpackage="Search.batch.immediately">
<classname="Team"table="team"lazy="false">
<idname="id"column="id">
<generatorclass="uuid.hex"></generator>
</id>
<propertyname="teamName"column="teamName"></property>
<!--需要批量加载,设置batch-size="2"-->
<setname="students"
lazy="false"
inverse="true"
outer-join="false"
batch-size="2"
>
<keycolumn="team_id"></key>
<one-to-manyclass="Search.batch.immediately.Student"/>
</set>
</class>
</hibernate-mapping>
再次运行测试程序,结果如下:
Hibernate:selectteam0_.idasid2_,team0_.teamNameasteamName2_fromteamteam0_
Hibernate:selectstudents0_.team_idasteam5_1_,students0_.idasid1_,students0_.idasid1_0_,students0_.cardIdascardId1_0_,students0_.nameasname1_0_,students0_.ageasage1_0_,students0_.team_idasteam5_1_0_fromstudentstudents0_wherestudents0_.team_idin(?,?)
Hibernate:selectstudents0_.team_idasteam5_1_,students0_.idasid1_,students0_.idasid1_0_,
students0_.cardIdascardId1_0_,students0_.nameasname1_0_,students0_.ageasage1_0_,students0_.team_idasteam5_1_0_fromstudentstudents0_wherestudents0_.team_idin(?,?)
Hibernate:selectstudents0_.team_idasteam5_1_,students0_.idasid1_,students0_.idasid1_0_,students0_.cardIdascardId1_0_,students0_.nameasname1_0_,students0_.ageasage1_0_,students0_.team_idasteam5_1_0_fromstudentstudents0_wherestudents0_.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hibernatesession的缓存中了
修改team.hbm.xml配置好lazy="true"
<?xmlversion="1.0"encoding="utf-8"?>
<!DOCTYPEhibernate-mappingPUBLIC"-//Hibernate/HibernateMappingDTD3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!--
MappingfileautogeneratedbyMyEclipse-HibernateTools
-->
<hibernate-mappingpackage="Search.batch.immediately">
<classname="Team"table="team"lazy="false">
<idname="id"column="id">
<generatorclass="uuid.hex"></generator>
</id>
<propertyname="teamName"column="teamName"></property>
<!--需要批量加载,设置batch-size="2"-->
<setname="students"
lazy="true"
inverse="true"
outer-join="false"
batch-size="2"
>
<keycolumn="team_id"></key>
<one-to-manyclass="Search.batch.immediately.Student"/>
</set>
</class>
</hibernate-mapping>
运行测试程序,结果如下:
Hibernate:selectteam0_.idasid2_,team0_.teamNameasteamName2_fromteamteam0_
Hibernate:selectstudents0_.team_idasteam5_1_,students0_.idasid1_,students0_.idasid1_0_,students0_.cardIdascardId1_0_,students0_.nameasname1_0_,students0_.ageasage1_0_,students0_.team_idasteam5_1_0_fromstudentstudents0_wherestudents0_.team_idin(?,?)
team1:2
team2:1
Hibernate:selectstudents0_.team_idasteam5_1_,students0_.idasid1_,students0_.idasid1_0_,students0_.cardIdascardId1_0_,students0_.nameasname1_0_,students0_.ageasage1_0_,students0_.team_idasteam5_1_0_fromstudentstudents0_wherestudents0_.team_idin(?,?)
team3:1
team4:1
Hibernate:selectstudents0_.team_idasteam5_1_,students0_.idasid1_,students0_.idasid1_0_,students0_.cardIdascardId1_0_,students0_.nameasname1_0_,students0_.ageasage1_0_,students0_.team_idasteam5_1_0_fromstudentstudents0_wherestudents0_.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