表结构:

实体类图:

CRUD:

Student:

package com.demo.model;

import java.io.UnsupportedEncodingException;
import java.util.Set; /**学生信息
* @author wobendiankun
*2014-10-19 下午08:54:29
*/
public class Student {
private int studentId ;
private String studentName ;
private int age;
private Set<Certificate> certificates ;
public int getStudentId() {
return studentId;
}
public void setStudentId(int studentId) {
this.studentId = studentId;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
String str="";
if(studentName!=null){
try {
str=new String(studentName.getBytes("UTF-8"));
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
}
return "Student [studentId=" + studentId + ", studentName="
+ str + ", age=" + age + "]";
}
public Set<Certificate> getCertificates() {
return certificates;
}
public void setCertificates(Set<Certificate> certificates) {
this.certificates = certificates;
} }

配置:

<?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.demo.model.Student" table="t_student">
<id name="studentId" column="student_id">
<generator class="sequence">
<param name="sequence">SEQ_T_STUDENT</param>
</generator>
</id>
<property name="studentName" column="student_name" />
<property name="age" /> <set name="certificates">
<key column="student_id"></key>
<one-to-many class="com.demo.model.Certificate"/>
</set>
</class>
</hibernate-mapping>

说明:

<set name="certificates">

<key column="student_id"></key>

<one-to-many class="com.demo.model.Certificate"/>

</set>

name:Student类的certificates属性名

<key column="student_id"></key> :关联字段名称

<one-to-many class="com.demo.model.Certificate"/>  : Set元素的类全名

add:

@Test
public void addTest() {
Certificate certificate1 = new Certificate();
certificate1.setCertificateName("aa");
certificate1.setCertificateNo("3a10001");
Certificate certificate2 = new Certificate();
certificate2.setCertificateName("bb");
certificate2.setCertificateNo("3a10002");
Set<Certificate> set=new HashSet<Certificate>();
set.add(certificate1);
set.add(certificate2); Student student = new Student();
student.setStudentName("钱六");
student.setAge(35);
student.setCertificates(set);
Session session = null;
try {
session = HibernateUtil.openSession();
session.beginTransaction();
session.save(student);
session.save(certificate1);
session.save(certificate2);
session.getTransaction().commit();
} catch (Exception e) {
session.getTransaction().rollback();
e.printStackTrace();
} finally {
HibernateUtil.closeSession(session);
} }

发出的SQL:

Hibernate: insert into t_student (student_name, age, student_id) values (?

, ?, ?)
Hibernate: insert into t_certificate (certificate_name, certificate_no, certificate_id) values (? , ? , ?)
Hibernate: insert into t_certificate (certificate_name, certificate_no, certificate_id) values (? , ?, ?)
Hibernate: update t_certificate set student_id=? where certificate_id=? Hibernate: update t_certificate set student_id=? where certificate_id=?

从两条update语句中,我们发现此时的关联字段由one(Student)的一方来维护。这个明显不合适

loadTest:

@Test
public void loadTest() {
Session session = null;
try {
session = HibernateUtil.openSession();
session.beginTransaction();
Student student =(Student) session.load(Student.class, 23);
System.out.println("姓名:"+student.getStudentName());
System.out.println("数量:"+student.getCertificates().size());
session.getTransaction().commit();
} catch (Exception e) {
session.getTransaction().rollback();
e.printStackTrace();
} finally {
HibernateUtil.closeSession(session);
} }

发出的SQL:

Hibernate: select student0_.student_id as student1_0_0_, student0_.student_name as student2_0_0_, student0_.age as age0_0_ from t_student student0_ where student0_.student_id=?
姓名:钱六
Hibernate: select certificat0_.student_id as student4_0_1_, certificat0_.certificate_id as certific1_1_, certificat0_.certificate_id as certific1_1_0_, certificat0_.certificate_name as certific2_1_0_, certificat0_.certificate_no as certific3_1_0_ from t_certificate certificat0_ where certificat0_.student_id=? 数量:2

loadLazyExtra:

在set标签中加入属性:lazy="extra"

<?

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.demo.model.Student" table="t_student">
<id name="studentId" column="student_id">
<generator class="sequence">
<param name="sequence">SEQ_T_STUDENT</param>
</generator>
</id>
<property name="studentName" column="student_name" />
<property name="age" /> <set name="certificates" lazy="extra"><!-- lazy="extra" -->
<key column="student_id"></key>
<one-to-many class="com.demo.model.Certificate"/>
</set>
</class>
</hibernate-mapping>

执行代码:

@Test
public void loadLazyExtraTest() {
Session session = null;
try {
session = HibernateUtil.openSession();
session.beginTransaction();
Student student =(Student) session.load(Student.class, 23);
System.out.println("姓名:"+student.getStudentName());
System.out.println("数量:"+student.getCertificates().size());
session.getTransaction().commit();
} catch (Exception e) {
session.getTransaction().rollback();
e.printStackTrace();
} finally {
HibernateUtil.closeSession(session);
}
}

发出的SQL:

Hibernate: select student0_.student_id as student1_0_0_, student0_.student_name as student2_0_0_, student0_.age as age0_0_ from t_student student0_ where student0_.student_id=?
姓名:钱六
Hibernate: select count(certificate_id) from t_certificate where student_id =?
数量:2

loadAssociatesTest:

@Test
public void loadAssociatesTest() {
Session session = null;
try {
session = HibernateUtil.openSession();
session.beginTransaction();
Student student =(Student) session.load(Student.class, 23);
System.out.println("姓名:"+student.getStudentName());
for(Certificate c:student.getCertificates()){
System.out.println("编号:"+c.getCertificateNo());
}
session.getTransaction().commit();
} catch (Exception e) {
session.getTransaction().rollback();
e.printStackTrace();
} finally {
HibernateUtil.closeSession(session);
}
}

发出的SQL:

Hibernate: select student0_.student_id as student1_0_0_, student0_.student_name as student2_0_0_, student0_.age as age0_0_ from t_student student0_ where student0_.student_id=?
姓名:钱六
Hibernate: select certificat0_.student_id as student4_0_1_, certificat0_.certificate_id as certific1_1_, certificat0_.certificate_id as certific1_1_0_, certificat0_.certificate_name as certific2_1_0_, certificat0_.certificate_no as certific3_1_0_ from t_certificate certificat0_ where certificat0_.student_id=?
编号:3a10001
编号:3a10002

第二条查询语句用于查询关联对象,事实上我们能够通过一条sql语句查询关联对象,例如以下:

select * from  t_student t1
inner join t_certificate t2 on t2.student_id=t1.student_id
where t1.student_id=23;

后面再进行优化

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