hibernate（4）:hibernate映射关系续
看完多对一，再来看看一对一的情况:
学生和证件是一对一的关系，并且学生ID和证件的ID是相同的。
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建表脚本：
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create table certificate( id varchar(100) not null default '', `describe` varchar(100) default '', primary key (id))create table student( id varchar(100) not null default'', name varchar(20) default'', `cardId` varchar(20) not null default'', age int(11) default'0', primary key(id))
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Student.java
package com.hibernate.model;public class Student {private String id; //标识IDprivate String cardId;//学号private String name;//姓名private int age;//年龄 private Certificate cer;//身份证private Team team;//班级public String getId() {return id;}public void setId(String id) {this.id = id;}public String getCardId() {return cardId;}public void setCardId(String cardId) {this.cardId = cardId;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Certificate getCer() {return cer;}public void setCer(Certificate cer) {this.cer = cer;}public Team getTeam() {return team;}public void setTeam(Team team) {this.team = team;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}}?
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package com.hibernate.model;public class Certificate {private String id;private String describe;private Student stu;public String getId() {return id;}public void setId(String id) {this.id = id;}public Student getStu() {return stu;}public void setStu(Student stu) {this.stu = stu;}public String getDescribe() {return describe;}public void setDescribe(String describe) {this.describe = describe;}}?
Student.hbm.xml?
<?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.hibernate.model.Student" table="student"><id name="id" unsaved-value="null"><generator type="string"/><!-- 没有指定 column，则列名和属性名是一样的 --><property name="name" type="string"/><property name="age" type="int"/><one-to-one name="cer" fetch="join" cascade="all"></one-to-one></class></hibernate-mapping>
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Certificate.hbm.xml
<?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.hibernate.model.Certificate" table="certificate" lazy="true"><id name="id"><!-- 下面表示引用Certificate的id引用Student的id --><generator column="`describe`" type="string"/><one-to-one name="stu" fetch="select" constrained="true" cascade="none"></one-to-one></class></hibernate-mapping>
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在hibernate.hbm.xml中加上映射
<mapping resource="Student.hbm.xml"></mapping> <mapping resource="Certificate.hbm.xml"></mapping>
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测试类
package com.hibernate.util;import org.hibernate.Session;import org.hibernate.Transaction;import com.hibernate.model.Certificate;import com.hibernate.model.Student;public class BM {public static void main(String[] args) {Session session = HibernateUtil.currentSession();Transaction tx = null;try {tx = session.beginTransaction();//实例化studentStudent stu = new Student();stu.setName("lisi");stu.setCardId("200202");stu.setAge(18);//实例化certificateCertificate certificate = new Certificate();certificate.setDescribe("lisi_certificate");//设置关联stu.setCer(certificate);certificate.setStu(stu);//只保存student，certificate会自动保存session.save(stu);tx.commit();} catch (Exception e) {e.printStackTrace();}finally{HibernateUtil.closeSession(session);}}}?
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再来看看一对一的另一种情况，即certificate表中添加一个stu_id字段，这个字段用来关联引用Student的id，
这也是在实际开发中用的最多的。
针对这种情况，只需要修改上例中的Certificate.hbm.xml文件，将one-to-one修改成many-to-one，如下所示，其它类不需要修改。
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<?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.hibernate.model.Certificate" table="certificate" lazy="true"><id name="id"><generator column="`describe`" type="string"/><!-- unique表示此字段值唯一，它可将many-to-one改造成one-to-one --><many-to-one name="stu" unique="true" column="stu_id"/></class></hibernate-mapping>
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Hibernate多对多映射
?假设有学生(student)和课程(course)的多对多映射。它们使用一张关联表(student_course)来保存关联关系。
建表脚本
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create table course( id varchar(32) not null default'', name varchar(20), primary key(id))create table student( id varchar(32) not null default'', cardId varchar(20), name varchar(20), age int(20))--学生与课程关联表create table student_course(??? student_id varchar(32) not null default'',??? course_id varchar(32) not null default'')
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Student.java
package com.hibernate.model;import java.util.HashSet;import java.util.Set;public class Student {private String id; //标识IDprivate String cardId;//学号private String name;//姓名private int age; //年龄 private Set courses = new HashSet();//课程public String getId() {return id;}public void setId(String id) {this.id = id;}public String getCardId() {return cardId;}public void setCardId(String cardId) {this.cardId = cardId;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public Set getCourses() {return courses;}public void setCourses(Set courses) {this.courses = courses;}}?
Course.java
package com.hibernate.model;import java.util.HashSet;import java.util.Set;public class Course {private String id;private String name;private Set students = new HashSet();public String getId() {return id;}public void setId(String id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Set getStudents() {return students;}public void setStudents(Set students) {this.students = students;}}?
Student.hbm.xml
<?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.hibernate.model.Student" table="student"><id name="id" unsaved-value="null"><generator type="string"/><!-- 没有指定 column，则列名和属性名是一样的 --><property name="name" type="string"/><property name="age" type="int"/><set name="courses" table="student_course" cascade="none" inverse="true"><!--下面这两个column都是对应关联表中的字段--><key column="student_id"/><many-to-many column="course_id"/></set></class></hibernate-mapping>
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Course.hbm.xml
<?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.hibernate.model.Course" table="course"><id name="id"><generator type="string"/><set name="students" table="student_course" cascade="save-update"><key column="course_id"/><many-to-many column="student_id"/></set></class></hibernate-mapping>
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测试类
package com.hibernate.util;import org.hibernate.Session;import org.hibernate.Transaction;import com.hibernate.model.Course;import com.hibernate.model.Student;public class BM {public static void main(String[] args) {saveStudentCourse();}public static void saveStudentCourse(){Session session = HibernateUtil.currentSession();Student student = null;Course course = null;Transaction tx = null;try{tx = session.beginTransaction();student = (Student) session.createQuery("from Student s where s.name='hp'").uniqueResult();course = (Course) session.createQuery("from Course s where s.name='English'").uniqueResult();student.getCourses().add(course);course.getStudents().add(student);tx.commit();}catch (Exception e) {e.printStackTrace();}finally{HibernateUtil.closeSession(session);}}}?
运行后，会自动在Student_Course表中保存关联数据。