Hibernate4检索策略
一、检索策略属性lazy(延迟检索)
lazy:true(默认)延迟检索; set端，一对多
lazy:false 立即检索; set端 一对多
lazy：extra 增强延迟检索; set端 一对多
lazy：proxy(默认) 延迟检索 many-to-one 多对一
lazy：no-proxy 无代理延迟检索 many-to-one 多对一（需要编译时字节码增强）
二、检索策略属性batch-size（批量检索）
延迟批量检索
立即批量检索
三、检索策略属性fetch(查询检索)
fetch：select(默认) 查询方式
fetch: subselect 子查询方式
fetch: join 迫切左外连接查询方式
四：上代码
1.配置hibernate.cfg.xml文件
<?xml version='1.0' encoding='utf-8'?>
<!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>
<!--数据库连接设置 -->
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
<property name="connection.username">root</property>
<property name="connection.password">123456</property>
<!-- 方言 -->
<property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>
<!-- 控制台显示SQL -->
<property name="show_sql">true</property>
<!-- 自动更新表结构 -->
<property name="hbm2ddl.auto">update</property>
<mapping resource="com/newbeedaly/model/Student.hbm.xml"/>
<mapping resource="com/newbeedaly/model/Class.hbm.xml"/>
</session-factory>
</hibernate-configuration>2.编写HibernateUtil类
package com.newbeedaly.util;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
public class HibernateUtil {
private static final SessionFactory sessionFactory=buildSessionFactory();
private static SessionFactory buildSessionFactory(){
Configuration configuration=new Configuration().configure(); // 实例化配置文件
ServiceRegistry serviceRegistry=new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build(); // 实例化服务登记
return configuration.buildSessionFactory(serviceRegistry); // 获取Session工厂
}
public static SessionFactory getSessionFactory(){
return sessionFactory;
}
}
3.编写Student、Class类
package com.newbeedaly.model;
public class Student {
private long id;
private String name;
private Class c;
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Class getC() {
return c;
}
public void setC(Class c) {
this.c = c;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + "]";
}
}
package com.newbeedaly.model;
import java.util.HashSet;
import java.util.Set;
public class Class {
private long id;
private String name;
private Set<Student> students=new HashSet<Student>();
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<Student> getStudents() {
return students;
}
public void setStudents(Set<Student> students) {
this.students = students;
}
}
4.编写Class.hbm.xml和Student.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.newbeedaly.model">
<class name="Class" table="t_class">
<id name="id" column="classId">
<generator class="native"></generator>
</id>
<property name="name" column="className"></property>
<set name="students" cascade="delete" inverse="true" lazy="false" batch-size="3" fetch="join" >
<key column="classId"></key>
<one-to-many class="com.newbeedaly.model.Student"/>
</set>
</class>
</hibernate-mapping><?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.newbeedaly.model">
<class name="Student" table="t_student">
<id name="id" column="stuId">
<generator class="native"></generator>
</id>
<property name="name" column="stuName"></property>
<!-- many-to-one 中添加 outer-join="true" 为左外连接 -->
<many-to-one name="c" column="classId" class="com.newbeedaly.model.Class" cascade="save-update" lazy="no-proxy"></many-to-one>
</class>
</hibernate-mapping>5.编写StudentTest测试类
package com.newbeedaly.service;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.newbeedaly.model.Class;
import com.newbeedaly.model.Student;
import com.newbeedaly.util.HibernateUtil;
public class StudentTest {
private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
private Session session;
@Before
public void setUp() throws Exception {
session=sessionFactory.openSession(); // 生成一个session
session.beginTransaction(); // 开启事务
}
@After
public void tearDown() throws Exception {
session.getTransaction().commit(); // 提交事务
session.close(); // 关闭session
}
@Test
public void testLazy1() {
Class c=(Class)session.get(Class.class, Long.valueOf(1));
Set<Student> studentList=(Set<Student>)c.getStudents();
System.out.println(studentList.size());
// studentList.iterator();
}
@Test
public void testLazy2() {
Student student=(Student)session.get(Student.class, Long.valueOf(1));
student.getC().getName();
}
@Test
public void testBatch1(){
List<Class> classList=session.createQuery("from Class").list();
Iterator it=classList.iterator();
Class c1=(Class)it.next();
Class c2=(Class)it.next();
Class c3=(Class)it.next();
c1.getStudents().iterator();
c2.getStudents().iterator();
c3.getStudents().iterator();
}
@Test
public void testBatch2(){
List<Class> classList=session.createQuery("from Class").list();
}
@Test
public void testFetch1(){
List<Class> classList=session.createQuery("from Class").list();
Iterator it=classList.iterator();
Class c1=(Class)it.next();
Class c2=(Class)it.next();
Class c3=(Class)it.next();
c1.getStudents().iterator();
c2.getStudents().iterator();
c3.getStudents().iterator();
}
@Test
public void testFetch2(){
Class c=(Class)session.get(Class.class, Long.valueOf(1));
}
}