Hibernate教程-Hibernate Many to Many Example using XML

我们可以使用list、set、bag、map等映射多对多关系。这里，我们将使用list来进行多对多映射。在这种情况下，将创建三个表。

多对多映射示例

在这个示例中，我们将使用list在问题和答案之间生成多对多关系。

1) 创建持久化类

有两个持久化类：Question.java和Answer.java。Question类包含Answer类的引用，反之亦然。

Question.java

package cn.javatiku;

import java.util.List;

public class Question {
    private int id;
    private String qname;
    private List<Answer> answers;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getQname() {
        return qname;
    }

    public void setQname(String qname) {
        this.qname = qname;
    }

    public List<Answer> getAnswers() {
        return answers;
    }

    public void setAnswers(List<Answer> answers) {
        this.answers = answers;
    }
}

Answer.java

package cn.javatiku;

import java.util.*;

public class Answer {
    private int id;
    private String answername;
    private String postedBy;
    private List<Question> questions;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getAnswername() {
        return answername;
    }

    public void setAnswername(String answername) {
        this.answername = answername;
    }

    public String getPostedBy() {
        return postedBy;
    }

    public void setPostedBy(String postedBy) {
        this.postedBy = postedBy;
    }

    public List<Question> getQuestions() {
        return questions;
    }

    public void setQuestions(List<Question> questions) {
        this.questions = questions;
    }
}

2) 为持久化类创建映射文件

这里，我们创建了question.hbm.xml和answer.hbm.xml文件来定义list。

question.hbm.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 5.3//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-5.3.dtd">
    
<hibernate-mapping>
    <class name="cn.javatiku.Question" table="ques1911">
        <id name="id" type="int">
            <column name="q_id" />
            <generator class="increment" />
        </id>
        <property name="qname" />
        <list name="answers" table="ques_ans1911" fetch="select" cascade="all">
            <key column="q_id" />
            <index column="type" />
            <many-to-many class="cn.javatiku.Answer" column="ans_id" />
        </list>
    </class>
</hibernate-mapping>

answer.hbm.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 5.3//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-5.3.dtd">
    
<hibernate-mapping>
    <class name="cn.javatiku.Answer" table="ans1911">
        <id name="id" type="int">
            <column name="ans_id" />
            <generator class="increment" />
        </id>
        <property name="answername" />
        <property name="postedBy" />
    </class>
</hibernate-mapping>

3) 创建配置文件

此文件包含有关数据库和映射文件的信息。

hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC 
    "-//Hibernate/Hibernate Configuration DTD 5.3//EN" 
    "http://hibernate.sourceforge.net/hibernate-configuration-5.3.dtd">
    
<hibernate-configuration>
    <session-factory>
        <property name="hbm2ddl.auto">create</property>
        <property name="dialect">org.hibernate.dialect.Oracle9Dialect</property>
        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:xe</property>
        <property name="connection.username">system</property>
        <property name="connection.password">jtp</property>
        <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
        <mapping resource="question.hbm.xml"/>
        <mapping resource="answer.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

4) 创建存储数据的类

StoreData.java

package cn.javatiku;

import java.util.ArrayList;
import org.hibernate.*;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;

public class StoreData {
    public static void main(String[] args) {
        StandardServiceRegistry ssr = new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();
        Metadata meta = new MetadataSources(ssr).getMetadataBuilder().build();
        SessionFactory factory = meta.getSessionFactoryBuilder().build();
        Session session = factory.openSession();
        Transaction t = session.beginTransaction();

        Answer ans1 = new Answer();
        ans1.setAnswername("Java is a programming language");
        ans1.setPostedBy("Ravi Malik");

        Answer ans2 = new Answer();
        ans2.setAnswername("Java is a platform");
        ans2.setPostedBy("Sudhir Kumar");

        Question q1 = new Question();
        q1.setQname("What is Java?");
        ArrayList<Answer> l1 = new ArrayList<Answer>();
        l1.add(ans1);
        l1.add(ans2);
        q1.setAnswers(l1);

        Answer ans3 = new Answer();
        ans3.setAnswername("Servlet is an Interface");
        ans3.setPostedBy("Jai Kumar");

        Answer ans4 = new Answer();
        ans4.setAnswername("Servlet is an API");
        ans4.setPostedBy("Arun");

        Question q2 = new Question();
        q2.setQname("What is Servlet?");
        ArrayList<Answer> l2 = new ArrayList<Answer>();
        l2.add(ans3);
        l2.add(ans4);
        q2.setAnswers(l2);

        session.persist(q1);
        session.persist(q2);

        t.commit();
        session.close();
        System.out.println("success");
    }
}

输出