我们可以使用列表, 集合, 包, 地图等来映射多对多关系。在这里, 我们将使用列表进行多对多映射。在这种情况下, 将创建三个表。
多对多映射示例
在此示例中, 我们将使用列表生成问题和答案之间的多对多关系。
1)创建持久性类
有两个持久性类Question.java和Answer.java。问题类包含答案类参考, 反之亦然。
Question.java
package com.srcmini;
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 com.srcmini;
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Mapping文件
在这里, 我们创建了用来定义列表的question.hbm.xml和answer.hbm.xml文件。
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="com.srcmini.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"></index>
<many-to-many class="com.srcmini.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="com.srcmini.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
该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)创建类来存储数据
StoreData.java
package com.srcmini;
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");
}
}
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