hibernate 一对一映射

[size=medium]（一）主键关联，即限制两张表的主键使用相同的值。

例如登记业务信息表的字段很多，可是平时有些字段用的并不是那么多，因此可以把平时比较少用的字段放到另一表中，这样平时加载业务信息表的时候就不用加载这些字段，效率比较高。这次就学生和档案的关系举例，每个学生都有一个档案，但平时档案用的不多而且内容多。

（1）编写POJO类
Tb_student.java

（一）主键关联，即限制两张表的主键使用相同的值。

例如登记业务信息表的字段很多，可是平时有些字段用的并不是那么多，因此可以把平时比较少用的字段放到另一表中，这样平时加载业务信息表的时候就不用加载这些字段，效率比较高。这次就学生和档案的关系举例，每个学生都有一个档案，但平时档案用的不多而且内容多。

（1）编写POJO类
Tb_student.java

public class TbStudent {
private Long sn;
private String name;
private String sex;
private String age;
public Long getSn() {
return sn;
}
public void setSn(Long sn) {
this.sn = sn;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getAge() {
return age;
}
public void setAge(String age) {
this.age = age;
}
}

tb_dossier.java
public class TbDossier {
private Long sn;
private String seniorSchool;
private String highSchool;
private String university;
private TbStudent tbStudent;

public TbStudent getTbStudent() {
return tbStudent;
}
public void setTbStudent(TbStudent tbStudent) {
this.tbStudent = tbStudent;
}
public Long getSn() {
return sn;
}
public void setSn(Long sn) {
this.sn = sn;
}
public String getSeniorSchool() {
return seniorSchool;
}
public void setSeniorSchool(String seniorSchool) {
this.seniorSchool = seniorSchool;
}
public String getHighSchool() {
return highSchool;
}
public void setHighSchool(String highSchool) {
this.highSchool = highSchool;
}
public String getUniversity() {
return university;
}
public void setUniversity(String university) {
this.university = university;
}
}

（2）映射文件

[color=blue]<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">
<hibernate-mapping package="com.longtop.entity">
<class name="TbStudent" table="TB_STUDENT">
<id name="sn" type="java.lang.Long" column="SN">
<generator class="sequence" >
<param name="sequence">seq_tb_student_sn</param>
</generator>
</id>
<property name="name" type="java.lang.String">
<column name="NAME" length="30" not-null="true" />
</property>

<property name="sex" type="java.lang.String">
<column name="SEX" length="20" />
</property>
<property name="age" type="java.lang.String">
<column name="AGE" length="20" />
</property>
</class>
</hibernate-mapping>
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping package="com.longtop.entity">
<class name="TbDossier" table="TB_DOSSIER">
<id name="sn" type="java.lang.Long" column="SN">
<generator class="foreign">
<param name="property">tbStudent</param>
</generator>
</id>
<property name="highSchool" type="java.lang.String">
<column name="HIGH_SCHOOL" length="30" not-null="true" />
</property>

<property name="seniorSchool" type="java.lang.String">
<column name="SENIOR_SCHOOL" length="20" />
</property>
<property name="university" type="java.lang.String">
<column name="UNIVERSITY" length="20" />
</property>
<one-to-one name="tbStudent" class="TbStudent"
cascade="all">
</one-to-one>
</class>
</hibernate-mapping>[/color]
tb_dossier的主键sn和对应的tb_student的主键sn是相同值，主要通过foreign的方式生成的，其中如果删除了可以级联操作cascade，即删除了tb_dossier，就会自动删除tb_student。

（4）测试类

public class OneToOne {

public static void main(String[] args) throws HibernateException {
SessionFactory sessions = new Configuration().configure().buildSessionFactory();
Session session = sessions.openSession();
Transaction tx = session.beginTransaction();
Long start = new Date().getTime();
System.out.println("starttime:"+start);

//添加、修改、删除方法
OneToOne.createStudent(session,
OneToOne.newStudent(session, "leochou", "26"),
"1中",
"1中",
"厦门大学");

OneToOne.updateDossier(session, new Long("11"));
// OneToOne.updateStudent(session, new Long("31"));
//
// OneToOne.deleteDossier(session, new Long("6"));

// session.save(OneToOne.createStudent(session, "lucy", "20"));
tx.commit();
session.close();

Long end = new Date().getTime();
System.out.println("endtime:"+end);
System.out.println("总共用了"+(end-start)+"的时间");

}
private static TbStudent newStudent(Session session,String name,String age) throws HibernateException {
TbStudent student = new TbStudent();
student.setName(name);
student.setAge(age);
return student;
}

private static void createStudent(Session session,
TbStudent student,
String highSchool,
String seniorSchool,
String university) throws HibernateException {
TbDossier dossier = new TbDossier();
dossier.setHighSchool(highSchool);
dossier.setSeniorSchool(seniorSchool);
dossier.setUniversity(university);
dossier.setTbStudent(student);
session.save(dossier);
}

private static void updateDossier(Session session,Long sn) throws HibernateException {
TbDossier dossier = (TbDossier) session.load(TbDossier.class, sn);
dossier.setSeniorSchool("八中");
dossier.getTbStudent().setName("change dossier");
session.update(dossier);
}

private static void updateStudent(Session session,Long sn) throws HibernateException {
TbStudent student = (TbStudent) session.load(TbStudent.class, sn);
student.setName("change student");
session.update(student);
}

private static void deleteDossier(Session session,Long sn) throws HibernateException {
TbDossier dossier = (TbDossier) session.load(TbDossier.class, sn);
session.delete(dossier);
}
}

注意：

为了保证每个同学都有一个档案，所以创建学生的时候，必须session.save(tbDossier)。这样才能tb_student与tb_dossier同时创建。

（二）tb_dossier通过student_sn外键关联tb_student。

两种实现方式的最大不同在于：1、tb_dossier必须新增一个字段student_sn存放对应的tb_student的sn，2、配置文件的不同，tb_dossier主键的生成不再以来tb_student的主键，独立生成。两个的关系用<many to one>表示，注意 unique="true"必须设为true。

[color=blue]<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping package="com.longtop.entity">
<class name="TbDossier" table="TB_DOSSIER">
<id name="sn" type="java.lang.Long" column="SN">
<generator class="sequence">
<param name="sequence">seq_tb_dossier_sn</param>
</generator>
</id>
<property name="highSchool" type="java.lang.String">
<column name="HIGH_SCHOOL" length="30" not-null="true" />
</property>

<property name="seniorSchool" type="java.lang.String">
<column name="SENIOR_SCHOOL" length="20" />
</property>
<property name="university" type="java.lang.String">
<column name="UNIVERSITY" length="20" />
</property>
<many-to-one name="tbStudent"
class="com.longtop.entity.TbStudent"
column="STUDENT_SN"
unique="true" cascade="all">
</many-to-one>
</class>
</hibernate-mapping>[/color]
[/size]