集合映射中的映射包（使用xml文件）
如果持久類有List對象，我們可以通過列表或者bag元素在映射文件中映射。 這個包(bag)就像List一樣，但它不需要索引元素。
在這裏，我們使用論壇的場景: 論壇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包(bag)：
<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
在這個例子中，我們將學習包(bag)的集合映射的完整示例。 這是一個bag的例子，如果它存儲的值不是實體引用，這就是爲什麼要使用element元素標籤來代替one-to-many。 如果您已經看過映射列表示例，這個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)。
創建一個Java項目：bagstring，完整的項目結構如下所示 -
1)創建持久類
這個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)創建持久化類的映射文件
在這裏，我們創建用於定義列表的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="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)創建配置文件
此文件包含有關數據庫和映射文件的信息。hibernate.cfg.xml 文件的內容如下 -
<?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
創建一個類：MainTest.java用於運行測試數據，在這個類中存儲Question類的數據。
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("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");
}
}如何獲取數據
在這裏，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，它從功能相關的兩個表中獲取數據。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();
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");
}
}運行示例代碼
首先運行 MainTest.java，將數據添加到數據庫表中，執行結果如下
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運行 FetchData.java，讀取上面創建的數據，如下結果 -
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 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