如果持久類具有Set對(duì)象，可以在映射文件中使用set元素映射Set集合。 set元素不需要索引元素。 List和Set之間的區(qū)別是： Set只存儲(chǔ)唯一的值。
我們來看看我們?nèi)绾卧谟成湮募袑?shí)現(xiàn)集合：
<class name="com.yiibai.Question" table="q102">
...
<set name="answers" table="ans102">
<key column="qid"></key>
<element column="answer" type="string"></element>
</set>
...
</class>
在這個(gè)例子中，我們將看到set的集合映射的完整示例。 這是存儲(chǔ)值不是實(shí)體引用的集合的示例，這就是為什么要使用 element 而不是one-to-many。
在這里，我們使用論壇的場(chǎng)景：論壇中一個(gè)問題有多個(gè)答案。
創(chuàng)建一個(gè)Java項(xiàng)目：setstring，完整的項(xiàng)目結(jié)果如下所示 -
這個(gè)持久化類定義了包含Set的類的屬性。Question.java代碼如下 -
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;
}
}
在這里，我們創(chuàng)建了用于定義列表的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="q102">
<id name="id">
<generator class="increment"></generator>
</id>
<property name="qname"></property>
<set name="answers" table="ans102">
<key column="qid"></key>
<element column="answer" type="string"></element>
</set>
</class>
</hibernate-mapping>
此文件包含有關(guān)數(shù)據(jù)庫(kù)和映射文件的信息。hibernate.cfg.xml文件的代碼如下所示 -
<?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>
在這個(gè)類中，我們存儲(chǔ)Question類的數(shù)據(jù)。MainTest.java文件中的代碼如下所示 -
package com.yiibai;
import java.util.ArrayList;
import java.util.HashSet;
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(kù)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();
HashSet<String> set1=new HashSet<String>();
set1.add("java is a programming language");
set1.add("java is a platform");
HashSet<String> set2=new HashSet<String>();
set2.add("Servlet is an Interface");
set2.add("Servlet is an API");
Question question1=new Question();
question1.setQname("What is Java?");
question1.setAnswers(set1);
Question question2=new Question();
question2.setQname("What is Servlet?");
question2.setAnswers(set2);
session.persist(question1);
session.persist(question2);
t.commit();
session.close();
System.out.println("success");
}
}
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 -
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?。? // 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(kù)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
Set<String> set = q.getAnswers();
Iterator<String> itr2 = set.iterator();
while (itr2.hasNext()) {
System.out.println(itr2.next());
}
}
session.close();
System.out.println("success");
}
}
首先運(yùn)行 MainTest.java 等到以下結(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 22:25:20 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: create table ans102 (qid integer not null, answer varchar(255)) engine=InnoDB
Hibernate: create table q102 (id integer not null, qname varchar(255), primary key (id)) engine=InnoDB
Hibernate: alter table ans102 add constraint FKce1yv9t7up0lavpmh8ry2gph5 foreign key (qid) references q102 (id)
Hibernate: select max(id) from q102
Hibernate: insert into q102 (qname, id) values (?, ?)
Hibernate: insert into q102 (qname, id) values (?, ?)
Hibernate: insert into ans102 (qid, answer) values (?, ?)
Hibernate: insert into ans102 (qid, answer) values (?, ?)
Hibernate: insert into ans102 (qid, answer) values (?, ?)
Hibernate: insert into ans102 (qid, answer) values (?, ?)
success
運(yùn)行 FetchData.java 讀取信息，到以下結(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 22:26:33 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 q102 question0_
Question Name: What is Java?
Hibernate: select answers0_.qid as qid1_0_0_, answers0_.answer as answer2_0_0_ from ans102 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 answer2_0_0_ from ans102 answers0_ where answers0_.qid=?
Servlet is an Interface
Servlet is an API
success
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