<class name="com.yiibai.Question" table="q100">  
       ...        
          <bag name="answers" table="ans100">  
          <key column="qid"></key>  
          <element column="answer" type="string"></element>  
          </bag>  

       ...  
</class>

在集合映射中映射包的示例

在這個(gè)例子中，我們將學(xué)習(xí)包(bag)的集合映射的完整示例。這是一個(gè)bag的例子，如果它存儲(chǔ)的值不是實(shí)體引用，這就是為什么要使用element元素標(biāo)簽來代替one-to-many。如果您已經(jīng)看過映射列表示例，這個(gè)示例與列表示例的所有情況下都是相同的，而是在文件映射中使用bag而不是列表(list)。

創(chuàng)建一個(gè)Java項(xiàng)目：bagstring，完整的項(xiàng)目結(jié)構(gòu)如下所示 -

1)創(chuàng)建持久類

這個(gè)持久化類定義了類的屬性，包括List。下面是 Question.java 文件的代碼 -

package com.yiibai;

import java.util.List;

public class Question {
    private int id;
    private String qname;
    private List<String> 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<String> getAnswers() {
        return answers;
    }

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

2)創(chuàng)建持久化類的映射文件

在這里，我們創(chuàng)建用于定義列表的question.hbm.xml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="com.yiibai.Question" table="q101">
        <id name="id">
            <generator class="increment"></generator>
        </id>
        <property name="qname"></property>

        <bag name="answers" table="ans101">
            <key column="qid"></key>
            <element column="answer" type="string"></element>
        </bag>
    </class>

</hibernate-mapping>

3)創(chuàng)建配置文件

此文件包含有關(guān)數(shù)據(jù)庫和映射文件的信息。hibernate.cfg.xml 文件的內(nèi)容如下 -

<?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">

<!-- Generated by MyEclipse Hibernate Tools. -->
<hibernate-configuration>

    <session-factory>
        <property name="hbm2ddl.auto">update</property>

        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/test</property>
        <property name="connection.username">root</property>
        <property name="connection.password">123456</property>
        <property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
        <property name="show_sql">true</property>

        <mapping resource="question.hbm.xml" />

    </session-factory>

</hibernate-configuration>

4)創(chuàng)建存儲(chǔ)數(shù)據(jù)的類

創(chuàng)建一個(gè)類：MainTest.java用于運(yùn)行測(cè)試數(shù)據(jù)，在這個(gè)類中存儲(chǔ)Question類的數(shù)據(jù)。

package com.yiibai;

import java.util.ArrayList;

import org.hibernate.*;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.*;

public class MainTest {
    public static void main(String[] args) {
        // 但在5.1.0版本匯總，hibernate則采用如下新方式獲取：
        // 1. 配置類型安全的準(zhǔn)服務(wù)注冊(cè)類，這是當(dāng)前應(yīng)用的單例對(duì)象，不作修改，所以聲明為final
        // 在configure("cfg/hibernate.cfg.xml")方法中，如果不指定資源路徑，默認(rèn)在類路徑下尋找名為hibernate.cfg.xml的文件
        final StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
                .configure("hibernate.cfg.xml").build();
        // 2. 根據(jù)服務(wù)注冊(cè)類創(chuàng)建一個(gè)元數(shù)據(jù)資源集，同時(shí)構(gòu)建元數(shù)據(jù)并生成應(yīng)用一般唯一的的session工廠
        SessionFactory sessionFactory = new MetadataSources(registry)
                .buildMetadata().buildSessionFactory();

        /**** 上面是配置準(zhǔn)備，下面開始我們的數(shù)據(jù)庫操作 ******/
        Session session = sessionFactory.openSession();// 從會(huì)話工廠獲取一個(gè)session

        // creating transaction object
        Transaction t = session.beginTransaction();

        ArrayList<String> list1 = new ArrayList<String>();
        list1.add("java is a programming language");
        list1.add("java is a platform");

        ArrayList<String> list2 = new ArrayList<String>();
        list2.add("Python is an Interface");
        list2.add("Python is an API");

        Question question1 = new Question();
        question1.setQname("What is Java?");
        question1.setAnswers(list1);

        Question question2 = new Question();
        question2.setQname("What is Python?");
        question2.setAnswers(list2);

        session.persist(question1);
        session.persist(question2);

        t.commit();

        session.close();
        System.out.println("success");

    }
}

如何獲取數(shù)據(jù)

在這里，我們使用HQL來獲取Question類的所有記錄，包括答案。在這種情況下，它從功能相關(guān)的兩個(gè)表中獲取數(shù)據(jù)。FetchData.java代碼如下所示 -

package com.yiibai;

import java.util.*;

import org.hibernate.*;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.*;

public class FetchData {
    public static void main(String[] args) {

        // 但在5.1.0版本匯總，hibernate則采用如下新方式獲取：
        // 1. 配置類型安全的準(zhǔn)服務(wù)注冊(cè)類，這是當(dāng)前應(yīng)用的單例對(duì)象，不作修改，所以聲明為final
        // 在configure("cfg/hibernate.cfg.xml")方法中，如果不指定資源路徑，默認(rèn)在類路徑下尋找名為hibernate.cfg.xml的文件
        final StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
                .configure("hibernate.cfg.xml").build();
        // 2. 根據(jù)服務(wù)注冊(cè)類創(chuàng)建一個(gè)元數(shù)據(jù)資源集，同時(shí)構(gòu)建元數(shù)據(jù)并生成應(yīng)用一般唯一的的session工廠
        SessionFactory sessionFactory = new MetadataSources(registry)
                .buildMetadata().buildSessionFactory();

        /**** 上面是配置準(zhǔn)備，下面開始我們的數(shù)據(jù)庫操作 ******/
        Session session = sessionFactory.openSession();// 從會(huì)話工廠獲取一個(gè)session

        // creating transaction object
        Transaction t = session.beginTransaction();

        Query query = session.createQuery("from Question");
        List<Question> list = query.list();

        Iterator<Question> itr = list.iterator();
        while (itr.hasNext()) {
            Question q = itr.next();
            System.out.println("Question Name: " + q.getQname());

            // printing answers
            List<String> list2 = q.getAnswers();
            Iterator<String> itr2 = list2.iterator();
            while (itr2.hasNext()) {
                System.out.println(itr2.next());
            }

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

    }
}

運(yùn)行示例代碼

首先運(yùn)行 MainTest.java，將數(shù)據(jù)添加到數(shù)據(jù)庫表中，執(zhí)行結(jié)果如下

log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Sun Mar 26 21:14:36 CST 2017 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Hibernate: select max(id) from q101
Hibernate: insert into q101 (qname, id) values (?, ?)
Hibernate: insert into q101 (qname, id) values (?, ?)
Hibernate: insert into ans101 (qid, answer) values (?, ?)
Hibernate: insert into ans101 (qid, answer) values (?, ?)
Hibernate: insert into ans101 (qid, answer) values (?, ?)
Hibernate: insert into ans101 (qid, answer) values (?, ?)
success

運(yùn)行 FetchData.java，讀取上面創(chuàng)建的數(shù)據(jù)，如下結(jié)果 -

log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Sun Mar 26 21:08:23 CST 2017 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Hibernate: select question0_.id as id1_1_, question0_.qname as qname2_1_ from q101 question0_
Question Name: What is Java?
Hibernate: select answers0_.qid as qid1_0_0_, answers0_.answer as answer2_0_0_ from ans101 answers0_ where answers0_.qid=?
java is a programming language
java is a platform
Question Name: What is Python?
Hibernate: select answers0_.qid as qid1_0_0_, answers0_.answer as answer2_0_0_ from ans101 answers0_ where answers0_.qid=?
Python is an Interface
Python is an API
success

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