Hibernate lazy loading single-ended correlation FOR
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Hibernate To load policy-Terminal associated lazy : That is, in <one-to-one>/<many-to-one> You can configure on the label
Lazy loading policy .
Can a value :false/proxy/no-proxy
false: Cancel the lazy loading policy, that is, while loading the object , Issuing the query statement, loading its associated object
proxy: It's hibernate on Singel associated default lazy loading policy , That is, only to its associated object method
It issues a query statement to query the object data, its associated object is a proxy class
no-proxy: This kind of lazy load characteristics need to be enhanced, use class no-proxy, Its associated object is not a proxy class
Note : In the class label configuration lazy The attribute does not affect to the associated object !!!
To many to one as an example the following cases:
package com.bjsxt.hibernate;
public class Group {
private int id;
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
package com.bjsxt.hibernate;
import java.util.Date;
public class User {
private int id;
private String name;
private Group group;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Group getGroup() {
return group;
}
public void setGroup(Group group) {
this.group = group;
}
}
Group.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.bjsxt.hibernate.Group" table="t_group">
<id name="id">
<generator/>
</id>
<property name="name"/>
</class>
</hibernate-mapping>
User.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.bjsxt.hibernate.User" table="t_user" >
<id name="id">
<generator/>
</id>
<property name="name"/>
<!--
<many-to-one name="group" column="relatedGroup" />
-->
<many-to-one name="group" column="relatedGroup"/>
</class>
</hibernate-mapping>
Generated data:
package com.bjsxt.hibernate;
import org.hibernate.Session;
public class InitData {
public static void main(String[] args) {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Group group = new Group();
group.setName("java Development Group ");
// The group is converted to a persistent object
session.save(group);
for (int i = 0; i < 10 ; i++) {
User user = new User();
user.setName("User_" + i);
// Establish relationships between objects
user.setGroup(group);
// Because the group is a persistent object , So you can successfully save
session.save(user);
}
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
}
Test Class:
package com.bjsxt.hibernate;
import org.hibernate.Session;
import junit.framework.TestCase;
/**
* All the property default lazy
* @author Administrator
*
*/
public class SingleEndTest1 extends TestCase {
public void testLoadUser() {
Session session = null;
try {
session = HibernateUtils.getSession();
// Never send query sql
User user = (User)session.load(User.class, 2);
// Will issue a query SQL, reprint data to User
System.out.println("user name=" + user.getName());
// Never send query sql
Group group = user.getGroup();
// Will issue a query SQL, reprint data to Group
System.out.println("related group=" + group.getName());
}catch(Exception e) {
e.printStackTrace();
}finally {
}
}
}
The lazy <class> tag is set to false
package com.bjsxt.hibernate;
import org.hibernate.Session;
import junit.framework.TestCase;
/**
* Will <class> The lazy in the label is set to false
* @author Administrator
*
*/
public class SingleEndTest2 extends TestCase {
public void testLoadUser() {
Session session = null;
try {
session = HibernateUtils.getSession();
// Will issue a query SQL, reprint data to User
User user = (User)session.load(User.class, 2);
// Never send query sql
System.out.println("user name=" + user.getName());
// Never send query sql
Group group = user.getGroup();
// Will issue a query SQL, reprint data to Group
System.out.println("related group=" + group.getName());
}catch(Exception e) {
e.printStackTrace();
}finally {
}
}
}
<class> Label lazy to keep the default settings, will <many-to-one> labels to add lazy = false
package com.bjsxt.hibernate;
import org.hibernate.Session;
import junit.framework.TestCase;
/**
* Keep <class> Label the lazy default settings in the
* Will <many-to-one> Label added lazy=false
* @author Administrator
*
*/
public class SingleEndTest3 extends TestCase {
public void testLoadUser() {
Session session = null;
try {
session = HibernateUtils.getSession();
// Does not issue a query sql
User user = (User)session.load(User.class, 2);
// Will issue a query SQL, here because many-to-one Setting the lazy = false so there will be group Also loads over here will issue two SQL
//Hibernate: select user0_.id as id0_0_, user0_.name as name0_0_, user0_.relatedGroup as relatedG3_0_0_ from t_user user0_ where user0_.id=?
//Hibernate: select group0_.id as id1_0_, group0_.name as name1_0_ from t_group group0_ where group0_.id=?
System.out.println("user name=" + user.getName());
// Never send query sql
Group group = user.getGroup();
// The previous single out data, is no longer issuing the query SQL
System.out.println("related group=" + group.getName());
}catch(Exception e) {
e.printStackTrace();
}finally {
}
}
}
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