一、Hinbernate中持久化类的关联关系
在数据库中，表表之间是通过外键关联的，在程序中是要转化为持久化类也就是(JAVA Bean)来实例的。
但在Hibernater中持久化的之间的映射关系，不是通外键建立关联，而是通过属性.主要有以下几种
- 一对一，
- 一对多(多对一)
- 多对多
关联方向：
- 单向关联
- 双向关联
二、一对多单向关联关系
2.1、建立数据库表
班级表，和学生表，学生生通过班级表中的，班级编号为外键
--班级表create table grade( gid number primary key, --班级ID gname varchar2(50), --班级名称 gdesc varchar2(50) --班级介绍);--学生表create table student( sid number primary key, --主键ID学生ID sname varchar2(20), --学生姓名 sex varchar2(20), --学生性别 gid number references grade(gid) ---外键班级ID);
2.2、建立持久化类和映射配置文件
班级和学生类
package entity;import java.util.HashSet;import java.util.Set;/* * 班级类 */public class Grade implements java.io.Serializable { // Fields private static final long serialVersionUID = 1L; private int gid; private String gname; private String gdesc; private Set<Student> students = new HashSet<Student> (); // Constructors /** default constructor */ public Grade() { } /** minimal constructor */ public Grade(int gid) { this.gid = gid; } /** full constructor */ public Grade(int gid, String gname, String gdesc, Set<Student> students) { this.gid = gid; this.gname = gname; this.gdesc = gdesc; this.students = students; } // Property accessors public int getGid() { return this.gid; } public void setGid(int gid) { this.gid = gid; } public String getGname() { return this.gname; } public void setGname(String gname) { this.gname = gname; } public String getGdesc() { return this.gdesc; } public void setGdesc(String gdesc) { this.gdesc = gdesc; } public Set<Student> getStudents() { return this.students; } public void setStudents(Set<Student> students) { this.students = students; }}
学生类
package entity;/* * 学生类 */public class Student implements java.io.Serializable { // Fields private static final long serialVersionUID = 1L; private int sid; private String sname; private String sex; // Constructors /** default constructor */ public Student() { } /** minimal constructor */ public Student(int sid) { this.sid = sid; } /** full constructor */ public Student(int sid, String sname, String sex ) { this.sid = sid; this.sname = sname; this.sex = sex; } // Property accessors public int getSid() { return this.sid; } public void setSid(int sid) { this.sid = sid; } public String getSname() { return this.sname; } public void setSname(String sname) { this.sname = sname; } public String getSex() { return this.sex; } public void setSex(String sex) { this.sex = sex; }}
hibernate.cf.xml和班级、学生的配置文件
<?xml version='1.0' encoding='UTF-8'?><!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="dialect"> org.hibernate.dialect.Oracle9Dialect </property> <property name="connection.url"> jdbc:oracle:thin:@localhost:1521:orcl </property> <property name="connection.username">root</property> <property name="connection.password">root</property> <property name="connection.driver_class"> oracle.jdbc.OracleDriver </property> <property name="show_sql">true</property> <property name="format_sql">true</property> <mapping resource="entity/Grade.hbm.xml" /> <mapping resource="entity/Student.hbm.xml" /></session-factory></hibernate-configuration>
持久类配置先来学生类
<?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="entity.Student" table="STUDENT" schema="ROOT"> <id name="sid" type="java.lang.Integer"> <column name="SID" precision="22" scale="0" /> <generator class="assigned" /> </id> <property name="sname" type="java.lang.String"> <column name="SNAME" length="20" /> </property> <property name="sex" type="java.lang.String"> <column name="SEX" length="20" /> </property> </class></hibernate-mapping>
班级类配置
<?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="entity.Grade" table="GRADE" schema="ROOT"> <id name="gid" type="java.lang.Integer"> <column name="GID" precision="22" scale="0" /> <generator class="assigned" /> </id> <property name="gname" type="java.lang.String"> <column name="GNAME" length="50" /> </property> <property name="gdesc" type="java.lang.String"> <column name="GDESC" length="50" /> </property> <!--建立set属性，也可以建立list和持久化类中一致就行 --> <set name="students"> <key> <!--这里的列是指学生表中的班级编号 --> <column name="GID" precision="22" scale="0" /> </key> <!-- 通过class属性指定set的属性 --> <one-to-many class="entity.Student" /> </set> </class></hibernate-mapping>
测试类
package Test;import java.util.Set;import org.hibernate.Session;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;import entity.Grade;import entity.Student;public class Demo1 { /** * 测试类 */ public static void main(String[] args) { save(); find(); update(); } public static void save() { // 声明班级对象，并赋值 Grade grade = new Grade(); grade.setGid(201504); grade.setGname("Java一班"); grade.setGdesc("刚开始学习JAVA"); // 声明2个学生对象 Student stu1 = new Student(); stu1.setSid(201504012); stu1.setSname("张三"); stu1.setSex("男"); Student stu2 = new Student(); stu2.setSid(201504013); stu2.setSname("李四"); stu2.setSex("女"); // 将学生添加到班级 grade.getStudents().add(stu1); grade.getStudents().add(stu2); // 建立session Session session = new Configuration().configure().buildSessionFactory() .openSession(); // 开始事务 Transaction transaction = session.beginTransaction(); // 保存班级 session.save(grade); // 保存学生 session.save(stu1); session.save(stu2); // 提交事务 transaction.commit(); // 关闭session session.close(); } /* * 将基中一个学生更改为别一个班级 */ public static void update() { // 声明班级对象，并赋值 Grade grade = new Grade(); grade.setGid(201506); grade.setGname("Java二班"); grade.setGdesc("学习JAVA二年级"); // 获取一个学生的信息 // 建立session Session session = new Configuration().configure().buildSessionFactory() .openSession(); // 开始事务 Transaction transaction = session.beginTransaction(); Student stu1=(Student) session.get(Student.class, 201504013); //将学生添加到这个新的班级 grade.getStudents().add(stu1); // 保存班级 session.save(grade); // 保存学生 session.save(stu1); // 提交事务 transaction.commit(); // 关闭session session.close(); } // 查询班级 public static void find() { // 建立session Session session = new Configuration().configure().buildSessionFactory() .openSession(); Grade g = (Grade) session.get(Grade.class, 201504); System.out.println("班级信息：" + g.getGid() + "\t" + g.getGname() + g.getGdesc()); // 通过班级获取这个班级的学生信息 System.out.println("201504班的学生信息如下:"); Set<Student> set = g.getStudents(); for (Student stu : set) { System.out.println(stu.getSid() + "\t" + stu.getSname() + "\t" + stu.getSex()); } }}
以上只上单向关联，一般都会有双向关联
同样要在学生类中添加Grade 属性
在学生类的配置文件中配置关联字段
二、建立双向关联
2.1、更改学生类和配置文件
package entity;/* * 学生类 */public class Student implements java.io.Serializable { // Fields private static final long serialVersionUID = 1L; private int sid; private String sname; private String sex; //增加班级属性 private Grade grade; // Constructors /** default constructor */ public Student() { } /** minimal constructor */ public Student(int sid) { this.sid = sid; } /** full constructor */ public Student(int sid, String sname, String sex ) { this.sid = sid; this.sname = sname; this.sex = sex; } // Property accessors public int getSid() { return this.sid; } public void setSid(int sid) { this.sid = sid; } public String getSname() { return this.sname; } public void setSname(String sname) { this.sname = sname; } public String getSex() { return this.sex; } public void setSex(String sex) { this.sex = sex; } public Grade getGrade() { return grade; } public void setGrade(Grade grade) { this.grade = grade; } }
配置文件
<?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="entity.Student" table="STUDENT" schema="ROOT"> <id name="sid" type="java.lang.Integer"> <column name="SID" precision="22" scale="0" /> <generator class="assigned" /> </id> <property name="sname" type="java.lang.String"> <column name="SNAME" length="20" /> </property> <property name="sex" type="java.lang.String"> <column name="SEX" length="20" /> </property> <!--配置grade属性 --> <many-to-one name="grade" class="entity.Grade"> <!--指定学生表中的外键 --> <column name="GID" /> </many-to-one> </class></hibernate-mapping>
2.2、测试类
建立双向关联后，就可以通过学生来获取班级信息
清空数据表中的数据
package Test;import org.hibernate.Session;import org.hibernate.cfg.Configuration;import entity.Student;public class Demo2 { /** * 测试类 */ public static void main(String[] args) { save();findByStu(); } public static void findByStu(){ Session session = new Configuration().configure().buildSessionFactory() .openSession(); //获取一个学生的信息 get方法为通过主键查询 Student stu=(Student) session.get(Student.class, 201504013); System.out.println("学生信息:\t"+stu.getSid()+"\t"+stu.getSname()+"\t"+stu.getSex()); //通过学生信息得到班级信息 System.out.println("这个学生的班级信息："+stu.getGrade().getGid()+"\t"+stu.getGrade().getGname()+"\t"+stu.getGrade().getGdesc()); }}public static void save() {// 声明班级对象，并赋值Grade grade = new Grade();grade.setGid(201504);grade.setGname("Java一班");grade.setGdesc("刚开始学习JAVA");// 声明2个学生对象Student stu1 = new Student();stu1.setSid(201504012);stu1.setSname("张三");stu1.setSex("男");stu1.setGrade(grade);Student stu2 = new Student();stu2.setSid(201504013);stu2.setSname("李四");stu2.setSex("女");stu2.setGrade(grade);// 将学生添加到班级/*grade.getStudents().add(stu1);grade.getStudents().add(stu2);*/// 建立sessionSession session = new Configuration().configure().buildSessionFactory().openSession();// 开始事务Transaction transaction = session.beginTransaction();// 保存班级session.save(grade);// 保存学生session.save(stu1);session.save(stu2);// 提交事务transaction.commit();// 关闭sessionsession.close();}
三、级联保存和删除
能不能只保存学生时，同时保存班级呢，或者保存班级时，同时保存学生呢3.1、cascade属性
保存班级时，同时保存学生信息
修改班级配置，在set标签中添加cascade属性,设置为save-update
<?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="entity.Grade" table="GRADE" schema="ROOT"> <id name="gid" type="java.lang.Integer"> <column name="GID" precision="22" scale="0" /> <generator class="assigned" /> </id> <property name="gname" type="java.lang.String"> <column name="GNAME" length="50" /> </property> <property name="gdesc" type="java.lang.String"> <column name="GDESC" length="50" /> </property> <!--建立set属性，也可以建立list和持久化类中一致就行 --> <set name="students" cascade="save-update"> <key> <!--这里的列是指学生表中的班级编号 --> <column name="GID" precision="22" scale="0" /> </key> <!-- 通过class属性指定set的属性 --> <one-to-many class="entity.Student" /> </set> </class></hibernate-mapping>
测试类
package Test;import org.hibernate.Session;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;import entity.Grade;import entity.Student;public class Demo3 { /** * @param args */ public static void main(String[] args) { save(); } public static void save() { // 声明班级对象，并赋值 Grade grade = new Grade(); grade.setGid(201504); grade.setGname("Java一班"); grade.setGdesc("刚开始学习JAVA"); // 声明2个学生对象 Student stu1 = new Student(); stu1.setSid(201504012); stu1.setSname("张三"); stu1.setSex("男"); stu1.setGrade(grade); Student stu2 = new Student(); stu2.setSid(201504013); stu2.setSname("李四"); stu2.setSex("女"); stu2.setGrade(grade); // 将学生添加到班级 grade.getStudents().add(stu1); grade.getStudents().add(stu2); // 建立session Session session = new Configuration().configure().buildSessionFactory() .openSession(); // 开始事务 Transaction transaction = session.beginTransaction(); // 保存班级 session.save(grade); // 保存学生 //session.save(stu1); //session.save(stu2); // 提交事务 transaction.commit(); // 关闭session session.close(); }}
反之，在学生类的配置文件one-many中添加cascade属性设置为save-update
<?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="entity.Student" table="STUDENT" schema="ROOT"> <id name="sid" type="java.lang.Integer"> <column name="SID" precision="22" scale="0" /> <generator class="assigned" /> </id> <property name="sname" type="java.lang.String"> <column name="SNAME" length="20" /> </property> <property name="sex" type="java.lang.String"> <column name="SEX" length="20" /> </property> <!--配置grade属性 --> <many-to-one name="grade" class="entity.Grade" cascade="save-update"> <!--指定学生表中的外键 --> <column name="GID" /> </many-to-one> </class></hibernate-mapping>
package Test;import org.hibernate.Session;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;import entity.Grade;import entity.Student;public class Demo3 { /** * @param args */ public static void main(String[] args) { save(); } public static void save() { // 声明班级对象，并赋值 Grade grade = new Grade(); grade.setGid(201504); grade.setGname("Java一班"); grade.setGdesc("刚开始学习JAVA"); // 声明2个学生对象 Student stu1 = new Student(); stu1.setSid(201504012); stu1.setSname("张三"); stu1.setSex("男"); stu1.setGrade(grade); Student stu2 = new Student(); stu2.setSid(201504013); stu2.setSname("李四"); stu2.setSex("女"); stu2.setGrade(grade); // 将学生添加到班级 grade.getStudents().add(stu1); grade.getStudents().add(stu2); // 建立session Session session = new Configuration().configure().buildSessionFactory() .openSession(); // 开始事务 Transaction transaction = session.beginTransaction(); // 保存班级 //session.save(grade); // 保存学生 session.save(stu1); session.save(stu2); // 提交事务 transaction.commit(); // 关闭session session.close(); }}
3.2、inverse属性
首先在班级类中设置invers属性为false时，删除班级
<?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="entity.Grade" table="GRADE" schema="ROOT"> <id name="gid" type="java.lang.Integer"> <column name="GID" precision="22" scale="0" /> <generator class="assigned" /> </id> <property name="gname" type="java.lang.String"> <column name="GNAME" length="50" /> </property> <property name="gdesc" type="java.lang.String"> <column name="GDESC" length="50" /> </property> <!--建立set属性，也可以建立list和持久化类中一致就行 --> <set name="students" cascade="save-update" inverse="false"> <key> <!--这里的列是指学生表中的班级编号 --> <column name="GID" precision="22" scale="0" /> </key> <!-- 通过class属性指定set的属性 --> <one-to-many class="entity.Student" /> </set> </class></hibernate-mapping>
测试类
package Test;import org.hibernate.Session;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;import entity.Grade;import entity.Student;public class Demo4 { /** * @param args */ public static void main(String[] args) { delete() ; } public static void delete() { // 建立session Session session = new Configuration().configure().buildSessionFactory() .openSession(); // 开始事务 Transaction transaction = session.beginTransaction(); // 保存班级 Grade grade=(Grade) session.get(Grade.class, 201504); // 保存学生 session.delete(grade); // 提交事务 transaction.commit(); // 关闭session session.close(); }}
结果：发现班级表中的班级已经删除，而学生表中数据没有删除，只是GID字段为NULL
下面将inverse设置为true时，添加新学生，和新的班级
<?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="entity.Grade" table="GRADE" schema="ROOT"> <id name="gid" type="java.lang.Integer"> <column name="GID" precision="22" scale="0" /> <generator class="assigned" /> </id> <property name="gname" type="java.lang.String"> <column name="GNAME" length="50" /> </property> <property name="gdesc" type="java.lang.String"> <column name="GDESC" length="50" /> </property> <!--建立set属性，也可以建立list和持久化类中一致就行 --> <set name="students" cascade="save-update" inverse="true"> <key> <!--这里的列是指学生表中的班级编号 --> <column name="GID" precision="22" scale="0" /> </key> <!-- 通过class属性指定set的属性 --> <one-to-many class="entity.Student" /> </set> </class></hibernate-mapping>
测试类
package Test;import org.hibernate.Session;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;import entity.Grade;import entity.Student;public class Demo4 { /** * @param args */ public static void main(String[] args) { delete() ; } public static void delete() { // 声明班级对象，并赋值 Grade grade = new Grade(); grade.setGid(201509); grade.setGname("Java三班"); grade.setGdesc("ASP.NET"); // 声明2个学生对象 Student stu1 = new Student(); stu1.setSid(201509009); stu1.setSname("王五"); stu1.setSex("女"); stu1.setGrade(grade); Student stu2 = new Student(); stu2.setSid(201509045); stu2.setSname("赵六"); stu2.setSex("女"); stu2.setGrade(grade); // 建立session Session session = new Configuration().configure().buildSessionFactory() .openSession(); // 开始事务 Transaction transaction = session.beginTransaction(); // 保存学生 session.save(stu1); session.save(stu2); // 提交事务 transaction.commit(); // 关闭session session.close(); }}
结果发现，我并没有用班级添加学生，也没有保存班级，只是保存了学生，班级信息一起保存了