hbernate学习（三）一对一双向关联
一对一映射：
1）主键关联。一对一默认使用的是立即加载，如果需要使用延迟加载，那么需要在one-to-one元素中将constrained属性设置为true，并且将待加载一方的class元素中lazy设置为true（或者不去设置，因为该属性的默认值是true）。一对一加载默认使用左外连接，可以通过修改fetch属性为select修改成迷城发送一条select语句的形式。
实例：
Student.java
package com.hibernate.one2one;public class Student {private int stuId;private String stuName;private CardId cardId;public int getStuId() {return stuId;}public void setStuId(int stuId) {this.stuId = stuId;}public String getStuName() {return stuName;}public void setStuName(String stuName) {this.stuName = stuName;}public CardId getCardId() {return cardId;}public void setCardId(CardId cardId) {this.cardId = cardId;}}
CardId.java
package com.hibernate.one2one;public class CardId {private int cardId;private String carNumber;private Student student;public int getCardId() {return cardId;}public void setCardId(int cardId) {this.cardId = cardId;}public String getCarNumber() {return carNumber;}public void setCarNumber(String carNumber) {this.carNumber = carNumber;}public Student getStudent() {return student;}public void setStudent(Student student) {this.student = student;}}
Student.hbm.xml
<?xml version="1.0" encoding="UTF-8"?><!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.hibernate.one2one.Student"> <id name="stuId" column="stuid"> <generator class="increment"></generator> </id> <property name="stuName" column="stuName" type="string"></property> <one-to-one name="cardId" class="com.hibernate.one2one.CardId" cascade="all" fetch="select"></one-to-one> </class> </hibernate-mapping>
CardId.hbm.xml
<?xml version="1.0" encoding="UTF-8"?><!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.hibernate.one2one.CardId" table="tb_card"> <id name="cardId" column="cardId"> <generator class="foreign"> <param name="property">student</param> </generator> </id> <property name="carNumber" type="string"></property> <one-to-one name="student" class="com.hibernate.one2one.Student" fetch="select"></one-to-one> </class> </hibernate-mapping>
hibernae.cfg.xml
<!DOCTYPE hibernate-configuration PUBLIC"-//Hibernate/Hibernate Configuration DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"><hibernate-configuration><session-factory><property name="connection.url">jdbc:mysql://localhost:3306/test</property><property name="connection.username">root</property><property name="connection.password">253503125</property><property name="connection.driver_class">com.mysql.jdbc.Driver</property><property name="dialect">org.hibernate.dialect.MySQLDialect</property><property name="show_sql">true</property><mapping resource="com/hibernate/one2one/CardId.hbm.xml"/><mapping resource="com/hibernate/one2one/Student.hbm.xml"/></session-factory></hibernate-configuration>
2）外键关联。本质上是一对多的退化形式。在many-to-one元素中增加unique=“true”属性就变成一对一。