一对一关系映射

主键关联

两个关联的实体在表中具有相同的主键值，这个主键可只由其中一个表生成，在另外一个表中通过映射文件中使用主键的foreign生成机制引用已经生成的主键值。

Student类

package Mapping2;public class Student {private Long id;private long studentNo;private String studentName;private int sage;private String major;/*进行一对一关联，双方互添引用对方对象的属性及方法 */private Card card;public Card getCard() {return card;}public void setCard(Card card) {this.card = card;}public Student() {}public Student(long studentNo, String studentName, int sage, String major) {super();this.studentNo = studentNo;this.studentName = studentName;this.sage = sage;this.major = major;}public Long getId() {return id;}public void setId(Long id) {this.id = id;}public long getStudentNo() {return studentNo;}public void setStudentNo(long studentNo) {this.studentNo = studentNo;}public String getStudentName() {return studentName;}public void setStudentName(String studentName) {this.studentName = studentName;}public int getSage() {return sage;}public void setSage(int sage) {this.sage = sage;}public String getMajor() {return major;}public void setMajor(String major) {this.major = major;}}

Student.hbm.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="Mapping2"><class name="Student" table="student" ><id name="id" column="id"><generator class="identity"/></id><property name="studentNo" type="long" column="student_no"/><property name="studentName" type="string" column="student_name"/><property name="sage" type="integer" column="sage"/><property name="major" type="string" column="major"/><one-to-one name="card" class="Mapping2.Card" cascade="all" fetch="join" /></class></hibernate-mapping>

Card类

package Mapping2;public class Card {private Long id;private String cardNo;private String major;private double balance;/*一对一关联，双方互添引用对方对象的属性及方法 */private Student student;public Student getStudent() {return student;}public void setStudent(Student student) {this.student = student;}public Card() {// TODO Auto-generated constructor stub}public Card(String cardNo, String major, double balance) {this.cardNo = cardNo;this.major = major;this.balance = balance;}public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getCardNo() {return cardNo;}public void setCardNo(String cardNo) {this.cardNo = cardNo;}public String getMajor() {return major;}public void setMajor(String major) {this.major = major;}public double getBalance() {return balance;}public void setBalance(double balance) {this.balance = balance;}}

Card.hbm.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">    <hibernate-mapping package="Mapping2"><class name="Card" table="card" lazy="true" ><id name="id" column="id"><generator class="foreign"><!-- 一对一关系映射，主键关联class是 foreign,外键关联是identity --><param name="property">student</param></generator></id><property name="CardNo" type="string" column="CardNo"/><property name="major" type="string" column="major"/><property name="balance" type="double" column="balance"/><!-- 一对一主键关联  --><one-to-one name="student" class="Mapping2.Student" constrained="true"  /></class></hibernate-mapping>

测试

package Mapping2;import org.hibernate.Transaction;import org.hibernate.Session;import util.HibernateUtil;public class OneToOnePrimaryKeyAssociation {public static void main(String[] args) {Session session = HibernateUtil.getSession();Transaction tx = session.beginTransaction();Student student = new Student(20120101,"Akbar Housein",20,"电子商务");Card card = new Card("110101","电子商务",1500.00);student.setCard(card);card.setStudent(student);session.save(student);tx.commit();}}

结果

外键关联

一对一的外键关联是指两个实体各自有自己的主键，但其中一个实体用外键引用另外一个实体。例如，Student实体和Card实体各自对应表的主键都是id，设在card表中还有一个studentId属性，它引用student表的id列，在card表中studentId就是外键。

若仍建立双向关联，则Student.hbm.xml无须修改，修改后的Card.hbm.xml如下：

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">    <hibernate-mapping package="Mapping2"><class name="Card" table="card" lazy="true" ><id name="id" column="id"><generator class="identity"><!-- 一对一关系映射，主键关联class是 foreign,外键关联是identity --><param name="property">student</param></generator></id><property name="CardNo" type="string" column="CardNo"/><property name="major" type="string" column="major"/><property name="balance" type="double" column="balance"/><!-- 一对一主键关联  <one-to-one name="student" class="Mapping2.Student" constrained="true"  />--> <!-- 一对一外键关联 --><many-to-one name="student" class="Mapping2.Student" column="studentId" unique="true" /><!-- 一对一关联实际是多对一关联的特例，当将<many-to-one>元素的unique属性值指定为true时，多对一的关联实际上变成了一对一的关联 --></class></hibernate-mapping>

上面Card类的基础上再加入studentId属性及setter、getter方法和新构造函数

/*一对一外键关联*/private Student studentId;public Student getStudentId() {return studentId;}public void setStudentId(Student studentId) {this.studentId = studentId;}public Card(String cardNo, String major, double balance,Student studentId) {this.cardNo = cardNo;this.major = major;this.balance = balance;this.studentId = studentId;}

将上面测试类中

Card card = new Card("110101","电子商务",1500.00);

改为

Card card = new Card("110101","电子商务",1500.00,student);

运行结果