集合映射中的映射列表（使用xml文件）
如果持久化類具有List對象，我們可以通過映射文件中的類的<list>元素或註釋來映射List。
在這裏，我們正在使用論壇的場景，其中一個問題有多個答案。
在這裏，我們使用論壇的場景，其中一個問題有多個答案。
我們來看看如何在映射文件中實現列表(List)：
<class name="com.yiibai.Question" table="q100">
...
<list name="answers" table="ans100">
<key column="qid"></key>
<index column="type"></index>
<element column="answer" type="string"></element>
</list>
...
</class>注：
List和Map是基於索引的集合，因此將在表中創建一個額外的列進行索引。
集合映射中的映射列表(List)示例
在這個例子中，我們將看到列表(List)在集合映射的完整示例。 這是List中存儲字符串值而不是實體引用的示例，這就是爲什麼要在列表元素中使用element標籤而不是one-to-many標籤的元素。
這個示例項目的完整結構如下圖所示 -
1)創建持久化類
這個持久化類定義了類的屬性，包括List。
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)創建持久化類的映射文件
在這裏，我們創建了用於定義列表的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="question_100">
<id name="id">
<generator class="increment"></generator>
</id>
<property name="qname"></property>
<list name="answers" table="answer_100">
<key column="qid"></key>
<index column="type"></index>
<element column="answer" type="string"></element>
</list>
</class>
</hibernate-mapping>3)創建配置文件
此文件包含有關數據庫和映射文件的信息。
文件：hibernate.hnm.xml 內容如下 -
<?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)創建存儲數據的類
在這個類(MainTest.java)中，用來存儲Question類的數據。使用HQL來獲取Answer類的所有記錄，包括答案。 在這個示例中，它從功能相關的兩個表中獲取數據。
package com.yiibai;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
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版本彙總，hibernate則採用如下新方式獲取：
// 1. 配置類型安全的準服務註冊類，這是當前應用的單例對象，不作修改，所以聲明爲final
// 在configure("cfg/hibernate.cfg.xml")方法中，如果不指定資源路徑，默認在類路徑下尋找名爲hibernate.cfg.xml的文件
final StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
.configure("hibernate.cfg.xml").build();
// 2. 根據服務註冊類創建一個元數據資源集，同時構建元數據並生成應用一般唯一的的session工廠
SessionFactory sessionFactory = new MetadataSources(registry)
.buildMetadata().buildSessionFactory();
/**** 上面是配置準備，下面開始我們的數據庫操作 ******/
Session session = sessionFactory.openSession();// 從會話工廠獲取一個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("Servlet is an Interface");
list2.add("Servlet is an API");
Question question1 = new Question();
question1.setQname("Java 是什麼?");
question1.setAnswers(list1);
Question question2 = new Question();
question2.setQname("Hibernate 是什麼?");
question2.setAnswers(list2);
session.persist(question1);
session.persist(question2);
t.commit();
// 查詢數據
Query<Question> 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> list21 = q.getAnswers();
Iterator<String> itr2 = list21.iterator();
while (itr2.hasNext()) {
System.out.println(itr2.next());
}
}
session.close();
System.out.println("success");
}
}執行上面代碼，得到以下輸出結果 -
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 05:18:56 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 question_100
Hibernate: insert into question_100 (qname, id) values (?, ?)
Hibernate: insert into question_100 (qname, id) values (?, ?)
Hibernate: insert into answer_100 (qid, type, answer) values (?, ?, ?)
Hibernate: insert into answer_100 (qid, type, answer) values (?, ?, ?)
Hibernate: insert into answer_100 (qid, type, answer) values (?, ?, ?)
Hibernate: insert into answer_100 (qid, type, answer) values (?, ?, ?)
Hibernate: select question0_.id as id1_1_, question0_.qname as qname2_1_ from question_100 question0_
Question Name: What is Java?
Hibernate: select answers0_.qid as qid1_0_0_, answers0_.answer as answer3_0_0_, answers0_.type as type2_0_ from answer_100 answers0_ where answers0_.qid=?
java is a programming language
java is a platform
Question Name: What is Servlet?
Hibernate: select answers0_.qid as qid1_0_0_, answers0_.answer as answer3_0_0_, answers0_.type as type2_0_ from answer_100 answers0_ where answers0_.qid=?
Servlet is an Interface
Servlet is an API
Question Name: What is Java?
Hibernate: select answers0_.qid as qid1_0_0_, answers0_.answer as answer3_0_0_, answers0_.type as type2_0_ from answer_100 answers0_ where answers0_.qid=?
java is a programming language
java is a platform
Question Name: What is Servlet?
Hibernate: select answers0_.qid as qid1_0_0_, answers0_.answer as answer3_0_0_, answers0_.type as type2_0_ from answer_100 answers0_ where answers0_.qid=?
Servlet is an Interface
Servlet is an API
Question Name: What is Java?
Hibernate: select answers0_.qid as qid1_0_0_, answers0_.answer as answer3_0_0_, answers0_.type as type2_0_ from answer_100 answers0_ where answers0_.qid=?
java is a programming language
java is a platform
Question Name: What is Servlet?
Hibernate: select answers0_.qid as qid1_0_0_, answers0_.answer as answer3_0_0_, answers0_.type as type2_0_ from answer_100 answers0_ where answers0_.qid=?
Servlet is an Interface
Servlet is an API
Question Name: Java 是什麼?
java is a programming language
java is a platform
Question Name: Hibernate 是什麼?
Servlet is an Interface
Servlet is an API
success