在數(shù)據(jù)庫中，表表之間是通過外鍵關(guān)聯(lián)的，在程序中是要轉(zhuǎn)化為持久化類也就是(java Bean)來實(shí)例的。

但在Hibernater中持久化的之間的映射關(guān)系，不是通外鍵建立關(guān)聯(lián)，而是通過屬性.主要有以下幾種

• 一對一，
• 一對多(多對一)
• 多對多

關(guān)聯(lián)方向：

• 單向關(guān)聯(lián)
• 雙向關(guān)聯(lián)

班級表，和學(xué)生表，學(xué)生生通過班級表中的，班級編號為外鍵

--班級表create table grade(       gid       number           PRimary key,  --班級ID       gname     varchar2(50),                  --班級名稱       gdesc     varchar2(50)                   --班級介紹);--學(xué)生表create table student(       sid       number           primary key,  --主鍵ID學(xué)生ID       sname     varchar2(20),            --學(xué)生姓名       sex       varchar2(20),            --學(xué)生性別       gid       number           references grade(gid) ---外鍵班級ID);

班級和學(xué)生類

package entity;import java.util.HashSet;import java.util.Set;/* * 班級類 */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;    }}

學(xué)生類

package entity;/* * 學(xué)生類 */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和班級、學(xué)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>

持久類配置先來學(xué)生類

<?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>

班級類配置

<?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屬性，也可以建立list和持久化類中一致就行  -->        <set name="students">            <key>            <!--這里的列是指學(xué)生表中的班級編號  -->                <column name="GID" precision="22" scale="0" />            </key>            <!-- 通過class屬性指定set的屬性 -->            <one-to-many class="entity.Student" />        </set>    </class></hibernate-mapping>

測試類

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 {    /**     * 測試類     */    public static void main(String[] args) {        save();         find();        update();    }    public static void save() {        // 聲明班級對象，并賦值        Grade grade = new Grade();        grade.setGid(201504);        grade.setGname("Java一班");        grade.setGdesc("剛開始學(xué)習(xí)JAVA");        // 聲明2個學(xué)生對象        Student stu1 = new Student();        stu1.setSid(201504012);        stu1.setSname("張三");        stu1.setSex("男");        Student stu2 = new Student();        stu2.setSid(201504013);        stu2.setSname("李四");        stu2.setSex("女");        // 將學(xué)生添加到班級        grade.getStudents().add(stu1);        grade.getStudents().add(stu2);        // 建立session        Session session = new Configuration().configure().buildSessionFactory()                .openSession();        // 開始事務(wù)        Transaction transaction = session.beginTransaction();        // 保存班級        session.save(grade);        // 保存學(xué)生        session.save(stu1);        session.save(stu2);        // 提交事務(wù)        transaction.commit();        // 關(guān)閉session        session.close();    }    /*     * 將基中一個學(xué)生更改為別一個班級     */    public static void update() {        // 聲明班級對象，并賦值        Grade grade = new Grade();        grade.setGid(201506);        grade.setGname("Java二班");        grade.setGdesc("學(xué)習(xí)JAVA二年級");        // 獲取一個學(xué)生的信息        // 建立session        Session session = new Configuration().configure().buildSessionFactory()                .openSession();        // 開始事務(wù)        Transaction transaction = session.beginTransaction();        Student stu1=(Student) session.get(Student.class, 201504013);        //將學(xué)生添加到這個新的班級        grade.getStudents().add(stu1);        // 保存班級        session.save(grade);        // 保存學(xué)生        session.save(stu1);        // 提交事務(wù)        transaction.commit();        // 關(guān)閉session        session.close();    }    // 查詢班級    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("班級信息：" + g.getGid() + "/t" + g.getGname()                + g.getGdesc());        // 通過班級獲取這個班級的學(xué)生信息        System.out.println("201504班的學(xué)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());        }    }}

以上只上單向關(guān)聯(lián)，一般都會有雙向關(guān)聯(lián)

同樣要在學(xué)生類中添加Grade 屬性

在學(xué)生類的配置文件中配置關(guān)聯(lián)字段

package entity;/* * 學(xué)生類 */public class Student implements java.io.Serializable {    // Fields    private static final long serialVersionUID = 1L;    private int sid;    private String sname;    private String sex;    //增加班級屬性    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屬性  -->        <many-to-one name="grade" class="entity.Grade">        <!--指定學(xué)生表中的外鍵  -->        <column name="GID" />        </many-to-one>    </class></hibernate-mapping>

建立雙向關(guān)聯(lián)后，就可以通過學(xué)生來獲取班級信息

清空數(shù)據(jù)表中的數(shù)據(jù)

package Test;import org.hibernate.Session;import org.hibernate.cfg.Configuration;import entity.Student;public class Demo2 {    /**     * 測試類     */    public static void main(String[] args) {　save();findByStu();    }        public static void findByStu(){        Session session = new Configuration().configure().buildSessionFactory()                .openSession();        //獲取一個學(xué)生的信息 get方法為通過主鍵查詢        Student stu=(Student) session.get(Student.class, 201504013);        System.out.println("學(xué)生信息:/t"+stu.getSid()+"/t"+stu.getSname()+"/t"+stu.getSex());        //通過學(xué)生信息得到班級信息        System.out.println("這個學(xué)生的班級信息："+stu.getGrade().getGid()+"/t"+stu.getGrade().getGname()+"/t"+stu.getGrade().getGdesc());    }}public static void save() {// 聲明班級對象，并賦值Grade grade = new Grade();grade.setGid(201504);grade.setGname("Java一班");grade.setGdesc("剛開始學(xué)習(xí)JAVA");// 聲明2個學(xué)生對象Student stu1 = new Student();stu1.setSid(201504012);stu1.setSname("張三");stu1.setSex("男");stu1.setGrade(grade);Student stu2 = new Student();stu2.setSid(201504013);stu2.setSname("李四");stu2.setSex("女");stu2.setGrade(grade);// 將學(xué)生添加到班級/*grade.getStudents().add(stu1);grade.getStudents().add(stu2);*/// 建立sessionSession session = new Configuration().configure().buildSessionFactory().openSession();// 開始事務(wù)Transaction transaction = session.beginTransaction();// 保存班級session.save(grade);// 保存學(xué)生session.save(stu1);session.save(stu2);// 提交事務(wù)transaction.commit();// 關(guān)閉sessionsession.close();}

能不能只保存學(xué)生時(shí)，同時(shí)保存班級呢，或者保存班級時(shí)，同時(shí)保存學(xué)生呢

保存班級時(shí)，同時(shí)保存學(xué)生信息

修改班級配置，在set標(biāo)簽中添加cascade屬性,設(shè)置為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屬性，也可以建立list和持久化類中一致就行  -->        <set name="students" cascade="save-update">            <key>            <!--這里的列是指學(xué)生表中的班級編號  -->                <column name="GID" precision="22" scale="0" />            </key>            <!-- 通過class屬性指定set的屬性 -->            <one-to-many class="entity.Student" />        </set>    </class></hibernate-mapping>

測試類

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() {        // 聲明班級對象，并賦值        Grade grade = new Grade();        grade.setGid(201504);        grade.setGname("Java一班");        grade.setGdesc("剛開始學(xué)習(xí)JAVA");        // 聲明2個學(xué)生對象        Student stu1 = new Student();        stu1.setSid(201504012);        stu1.setSname("張三");        stu1.setSex("男");        stu1.setGrade(grade);                        Student stu2 = new Student();        stu2.setSid(201504013);        stu2.setSname("李四");        stu2.setSex("女");        stu2.setGrade(grade);        // 將學(xué)生添加到班級        grade.getStudents().add(stu1);        grade.getStudents().add(stu2);        // 建立session        Session session = new Configuration().configure().buildSessionFactory()                .openSession();        // 開始事務(wù)        Transaction transaction = session.beginTransaction();        // 保存班級        session.save(grade);        // 保存學(xué)生        //session.save(stu1);        //session.save(stu2);        // 提交事務(wù)        transaction.commit();        // 關(guān)閉session        session.close();    }}

反之，在學(xué)生類的配置文件one-many中添加cascade屬性設(shè)置為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屬性  -->        <many-to-one name="grade" class="entity.Grade" cascade="save-update">        <!--指定學(xué)生表中的外鍵  -->        <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() {        // 聲明班級對象，并賦值        Grade grade = new Grade();        grade.setGid(201504);        grade.setGname("Java一班");        grade.setGdesc("剛開始學(xué)習(xí)JAVA");        // 聲明2個學(xué)生對象        Student stu1 = new Student();        stu1.setSid(201504012);        stu1.setSname("張三");        stu1.setSex("男");        stu1.setGrade(grade);                        Student stu2 = new Student();        stu2.setSid(201504013);        stu2.setSname("李四");        stu2.setSex("女");        stu2.setGrade(grade);        // 將學(xué)生添加到班級        grade.getStudents().add(stu1);        grade.getStudents().add(stu2);        // 建立session        Session session = new Configuration().configure().buildSessionFactory()                .openSession();        // 開始事務(wù)        Transaction transaction = session.beginTransaction();        // 保存班級        //session.save(grade);        // 保存學(xué)生        session.save(stu1);        session.save(stu2);        // 提交事務(wù)        transaction.commit();        // 關(guān)閉session        session.close();    }}

首先在班級類中設(shè)置invers屬性為false時(shí)，刪除班級

<?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屬性，也可以建立list和持久化類中一致就行  -->        <set name="students" cascade="save-update" inverse="false">            <key>            <!--這里的列是指學(xué)生表中的班級編號  -->                <column name="GID" precision="22" scale="0" />            </key>            <!-- 通過class屬性指定set的屬性 -->            <one-to-many class="entity.Student" />        </set>    </class></hibernate-mapping>

測試類

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();        // 開始事務(wù)        Transaction transaction = session.beginTransaction();        // 保存班級        Grade grade=(Grade) session.get(Grade.class, 201504);        // 保存學(xué)生        session.delete(grade);        // 提交事務(wù)        transaction.commit();        // 關(guān)閉session        session.close();    }}

結(jié)果：發(fā)現(xiàn)班級表中的班級已經(jīng)刪除，而學(xué)生表中數(shù)據(jù)沒有刪除，只是GID字段為NULL

下面將inverse設(shè)置為true時(shí)，添加新學(xué)生，和新的班級

<?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屬性，也可以建立list和持久化類中一致就行  -->        <set name="students" cascade="save-update" inverse="true">            <key>            <!--這里的列是指學(xué)生表中的班級編號  -->                <column name="GID" precision="22" scale="0" />            </key>            <!-- 通過class屬性指定set的屬性 -->            <one-to-many class="entity.Student" />        </set>    </class></hibernate-mapping>

測試類

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() {                // 聲明班級對象，并賦值                Grade grade = new Grade();                grade.setGid(201509);                grade.setGname("Java三班");                grade.setGdesc("asp.net");                // 聲明2個學(xué)生對象                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("趙六");                stu2.setSex("女");                stu2.setGrade(grade);                // 建立session        Session session = new Configuration().configure().buildSessionFactory()                .openSession();        // 開始事務(wù)        Transaction transaction = session.beginTransaction();                    // 保存學(xué)生        session.save(stu1);        session.save(stu2);        // 提交事務(wù)        transaction.commit();        // 關(guān)閉session        session.close();    }}

結(jié)果發(fā)現(xiàn)，我并沒有用班級添加學(xué)生，也沒有保存班級，只是保存了學(xué)生，班級信息一起保存了