Hibernate List集合映射简单例子

最新推荐文章于 2021-02-23 16:27:52 发布

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本文详细介绍了如何使用Hibernate框架实现数据库表与Java实体类的映射，并通过示例展示了如何操作数据库数据。

建两个相应的表：

email_list:

create table email_list(
id int(11) not null,
email_id int(11) not null,
email varchar(100) not null default ''
)engine=innodb default charset=gbk;

user_list:

create table user_list(
id int(11) not null auto_increment,
name varchar(100) not null default '',
primary key(id)
)engine=innodb default charset=gbk;

建立UserList.java实体类：

package collect.list;

import java.util.ArrayList;
import java.util.List;

public class UserList implements java.io.Serializable {
	// Fields
	private Integer id;
	private String name;
	private List emails = new ArrayList();

	// Constructors
	/** default constructor */
	public UserList() {
	}

	/** full constructor */
	public UserList(String name) {
		this.name = name;
	}

	// Property accessors

	public Integer getId() {
		return this.id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getName() {
		return this.name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public List getEmails() {
		return emails;
	}

	public void setEmails(List emails) {
		this.emails = emails;
	}

	public void addEmail(String email) {
		emails.add(email);
	}

	public void removeEmail(String email) {
		emails.remove(email);
	}
}

建立映射文件UserList.hbm.xml：

<?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">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="collect.list.UserList" table="user_list" catalog="ssh">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="name" length="100" not-null="true" />
        </property>
        <list name="emails" table="email_list">
        	<key column="id"></key>
        	<index column="email_id"></index>
        	<element type="java.lang.String" column="email"></element>
        </list>
    </class>
</hibernate-mapping>

注解：其中List类型映射中<index>标签指定email_id字段记录List元素序号。

将该映射文件加入到Hibernate配置文件中，建立测试类Test.java：

package collect.list;

import java.util.List;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public class Test {

	public static void main(String[] args) {
		// Configuration管理Hibernate配置
		Configuration config = new Configuration().configure();
		// 根据Configuration建立 SessionFactory
		// SessionFactory用来建立Session
		SessionFactory sessionFactory = config.buildSessionFactory();

		// 创建实例
		UserList user1 = new UserList();
		user1.setName("user1");
		user1.addEmail("email1");
		user1.addEmail("email2");
		user1.addEmail("email1");
		user1.addEmail("email3");

		UserList user2 = new UserList();
		user2.setName("user2");
		user2.addEmail("email3");
		user2.addEmail("email4");


		// 添加数据
		Session session = sessionFactory.openSession();
		Transaction tx = null;
		try {
			tx = session.beginTransaction();
			// INSERT到数据库
			session.save(user1);
			session.save(user2);
			tx.commit();
		} catch (RuntimeException e) {
			if (tx != null)
				tx.rollback();
			throw e;
		} finally {
			session.close();
		}

		// 关闭sessionFactory
		sessionFactory.close();

	}

}

日志配置文件log4j.properties：（通过查看合适的日志，便于分析运行过程）

### direct log messages to stdout ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

### direct messages to file hibernate.log ###
#log4j.appender.file=org.apache.log4j.FileAppender
#log4j.appender.file.File=hibernate.log
#log4j.appender.file.layout=org.apache.log4j.PatternLayout
#log4j.appender.file.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

### set log levels - for more verbose logging change 'info' to 'debug' ###

#log4j.rootLogger=warn, stdout
log4j.rootLogger=debug, stdout

#log4j.logger.org.hibernate=info
log4j.logger.org.hibernate=warn

### log HQL query parser activity
#log4j.logger.org.hibernate.hql.ast.AST=debug

### log just the SQL
log4j.logger.org.hibernate.SQL=debug

### log JDBC bind parameters ###
#log4j.logger.org.hibernate.type=info
log4j.logger.org.hibernate.type=warn

### log schema export/update ###
log4j.logger.org.hibernate.tool.hbm2ddl=warn

### log HQL parse trees
log4j.logger.org.hibernate.hql=debug

### log cache activity ###
log4j.logger.org.hibernate.cache=debug

### log transaction activity
log4j.logger.org.hibernate.transaction=warn

### log JDBC resource acquisition
log4j.logger.org.hibernate.jdbc=warn

### enable the following line if you want to track down connection ###
### leakages when using DriverManagerConnectionProvider ###
#log4j.logger.org.hibernate.connection.DriverManagerConnectionProvider=trace

运行结果：

控制台：

22:21:25,196 DEBUG SQL:346 - insert into ssh.user_list (name) values (?)
22:21:25,213 DEBUG SQL:346 - insert into ssh.user_list (name) values (?)
22:21:25,220 DEBUG SQL:346 - insert into email_list (id, email_id, email) values (?, ?, ?)
22:21:25,221 DEBUG SQL:346 - insert into email_list (id, email_id, email) values (?, ?, ?)
22:21:25,221 DEBUG SQL:346 - insert into email_list (id, email_id, email) values (?, ?, ?)
22:21:25,223 DEBUG SQL:346 - insert into email_list (id, email_id, email) values (?, ?, ?)
22:21:25,223 DEBUG SQL:346 - insert into email_list (id, email_id, email) values (?, ?, ?)
22:21:25,224 DEBUG SQL:346 - insert into email_list (id, email_id, email) values (?, ?, ?)

数据库：

对比Set集合映射中没有email_id字段，就是因为Set集合中的元素是无序不重复的，而List集合中元素是有序可重复的。对于Set集合而言，email中重复的记录会被覆盖，这样一来email_id字段就没有意义了。而对于List集合，email联合字段email_id才可唯一确定一个有序email，emial_id相当于是List类型映射中<index>标签的index(索引,从下标0开始)了。