Hibernate之映射值类型集合(映射set)

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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">  <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>  <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>  <property name="hibernate.connection.username">system</property>  <property name="hibernate.connection.password">password</property>  <property name="hibernate.c3p0.max_size">20</property>  <property name="hibernate.c3p0.min_size">5</property>  <property name="hibernate.c3p0.timeout">120</property>  <property name="hibernate.c3p0.max_statements">100</property>  <property name="hibernate.c3p0.idle_test_period">120</property>  <property name="hibernate.c3p0.acquire_increment">2</property>  <property name="dialect">org.hibernate.dialect.OracleDialect</property>  <property name="show_sql">true</property>  <property name="hibernate.format_sql">true</property>  <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,NAMEITEM_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。