Hibernate之映射值类型集合(映射list)

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.ArrayList; import java.util.List; public class Item implements Serializable{ private String id; private String name; //请注意这一行 private List<String> images = new ArrayList<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 List<String> getImages() { return images; } public void setImages(List<String> images) { this.images = images; } }  

 

pojo/Item.hbm.xml:

根据测试，list中有null值时,null值是插不进集合表中的，但也不会报错。

<?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"/> <list name="images" table="ITEM_IMAGE"> <key column="ITEM_ID" not-null="true"/> <list-index column="POSITION"/> <element type="string" column="FILENAME" not-null="true"/> </list> </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.ArrayList; import java.util.List; import org.hibernate.Session; import org.hibernate.Transaction; import pojo.Item; public class Manager { public static void main(String[] args) { //这里用List List<String> s = new ArrayList<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_IMAGE表： ITEM_ID, POSITION, FILENAME 

 

输出sql:

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

 

 

 

 

 

上例中，<list>映射需要把一个索引列新增到集合表。索引列定义元素在集合中的位置。因而，hibernate能够保存集合元素的顺序。映射集合为<list>。

集合表的主键是ITEM_ID和POSITION的复合。注意，现在允许重复元素了，这与列表的语义一致。

持久化列表的索引从0开始，可以改变它，例如在映射中使用<list-index base="1".../>。注意，如果数据库中的索引数字不连续，hibernate就会把空元素添加到java列表中。

 

另一种方法，可以映射一个java数组而不是列表。hibernate支持这个。数组映射事实上与前一个例子是等同的，除了使用不同的元素和属性之外(<array>和<array-index>)。然而，基于前面阐述过的原因，hibernate应用程序很少使用数组。