Hibernate之映射值类型集合(映射set)

pom.xml:

]<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion>
<groupId>hibernateTest</groupId>
<artifactId>hibernateTest</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
<name>hibernateTest</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>3.3.1.GA</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-nop</artifactId>
<version>1.5.2</version>
</dependency>
<dependency>
<groupId>javassist</groupId>
<artifactId>javassist</artifactId>
<version>3.4.GA</version>
</dependency>
<dependency>
<groupId>c3p0</groupId>
<artifactId>c3p0</artifactId>
<version>0.9.1</version>
</dependency>
<dependency>
<groupId>com.oracle</groupId>
<artifactId>ojdbc14</artifactId>
<version>10.2.0.3.0</version>
<scope>runtime</scope>
</dependency>
</dependencies>
<build>
<finalName>hibernateTest</finalName>
<resources>
<resource>
<directory>src/main/resources</directory>
</resource>
<resource>
<directory>src/main/java</directory>
<excludes>
<exclude>**/*.java</exclude>
</excludes>
</resource>
</resources>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.6</source>
<target>1.6</target>
<encoding>UTF-8</encoding>
</configuration>
</plugin>
</plugins>
</build>
</project>

resources/hibernate.cfg.xml:

]<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration
PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory name="sessionFactory">
<!-- 指定连接数据库所用的驱动 -->
<property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
<!-- 指定连接数据库的url，hibernate连接的数据库名 -->
<property name="hibernate.connection.url">jdbc:oracle:thin:@localhost:1521:XE</property>
<property name="hibernate.connection.useUnicode">true</property>
<property name="hibernate.connection.characterEncoding">gbk</property>
<!-- 指定连接数据库的用户名 -->
<property name="hibernate.connection.username">system</property>
<!-- 指定连接数据库的密码 -->
<property name="hibernate.connection.password">password</property>
<!-- 指定连接池里最大连接数 -->
<property name="hibernate.c3p0.max_size">20</property>
<!-- 指定连接池里最小连接数 -->
<property name="hibernate.c3p0.min_size">5</property>
<!-- 指定连接池里连接的超时时长,以秒为单位 -->
<property name="hibernate.c3p0.timeout">120</property>
<!-- 指定连接池里最大缓存多少个Statement对象 -->
<property name="hibernate.c3p0.max_statements">100</property>
<!-- 每隔XX秒检查连接池里的空闲连接 ，单位是秒 -->
<property name="hibernate.c3p0.idle_test_period">120</property>
<!-- 当连接池里面的连接用完的时候，C3P0一次获取的新的连接数 -->
<property name="hibernate.c3p0.acquire_increment">2</property>
<!-- 指定数据库方言 -->
<property name="dialect">org.hibernate.dialect.OracleDialect</property>
<!-- 显示Hibernate持久化操作所生成的SQL -->
<property name="show_sql">true</property>
<!-- 将SQL脚本进行格式化后再输出 -->
<property name="hibernate.format_sql">true</property>
<!-- 罗列所有的映射文件 -->
<mapping resource="pojo/Item.hbm.xml" />
</session-factory>
</hibernate-configuration>

pojo/Item.java:

]package pojo;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
public class Item implements Serializable{
private String id;
private String name;
private Set<String> images = new HashSet<String>();

public String getId() {
return id;
}
@SuppressWarnings("unused")
private void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<String> getImages() {
return images;
}
public void setImages(Set<String> images) {
this.images = images;
}
}

pojo/Item.hbm.xml:

在<element>元素上加了not-null="true",为什么还能插入null值呢？？？？？？？？？？？？？？？？？？？？？奇怪了！！！！！！

]<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="pojo">
<class name="Item" table="ITEM" dynamic-insert="true" dynamic-update="true">
<id name="id" column="ITEM_ID" type="string">
<generator class="uuid.hex" />
</id>
<property name="name" column="NAME" type="string"/>
<set name="images" table="ITEM_IMAGE">
<key column="ITEM_ID" not-null="true"/>
<element type="string" column="FILENAME" not-null="true"/>
</set>
</class>
</hibernate-mapping>

util/HibernateUtil.java:

]package util;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtil {
private static SessionFactory sessionFactory;
static{
try {
sessionFactory = new Configuration().configure().buildSessionFactory();
} catch (Throwable e) {
throw new ExceptionInInitializerError(e);
}
}
public static SessionFactory getSessionFactory(){
return sessionFactory;
}
public static void shutdown(){
getSessionFactory().close();
}
}

util/Manager.java:

]package util;
import java.util.HashSet;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.Transaction;
import pojo.Item;
public class Manager {
public static void main(String[] args) {

Set<String> s = new HashSet<String>();
s.add("aaa.jpg");
s.add("bbb.jpg");
s.add("ccc.jpg");
Item item = new Item();
item.setImages(s);
item.setName("fuhaidong");

Session session = HibernateUtil.getSessionFactory().openSession();
Transaction transaction = session.beginTransaction();
session.save(item);
transaction.commit();
session.close();
}
}

表结构：

]ITEM表：
ITEM_ID,
NAME
ITEM_FILENAME表：
ITEM_ID,
FILENAME

输出sql日志：

]Hibernate:
insert
into
ITEM
(NAME, ITEM_ID)
values
(?, ?)
Hibernate:
insert
into
ITEM_IMAGE
(ITEM_ID, FILENAME)
values
(?, ?)
Hibernate:
insert
into
ITEM_IMAGE
(ITEM_ID, FILENAME)
values
(?, ?)
Hibernate:
insert
into
ITEM_IMAGE
(ITEM_ID, FILENAME)
values
(?, ?)

上例中，图片的文件名保存在具名ITEM_IMAGE的集合表中。从数据库的观点来看，这张表是单个的实体，是一张单独的表，但是hibernate为你隐藏了这一点。<key>元素在引用自己的实体的主键ITEM_ID的集合表中，声明了外键列。<element>标签把这个集合声明为值类型实例的一个集合---在这个例子中，是字符串的集合。该集无法包含重复元素，因此ITEM_IMAGE集合表的主键是<set>声明中这两个列的复合：ITEM_ID和FILENAME。