hibernate之多态关联(多态的多对一关联或者多态的一对一关联,利用union-subclass)

hibernate之多态关联(多态的多对一关联或者多态的一对一关联)

不必做任何特别的事情来启用hibernate中的多态关联，在关联映射中指定任何被映射的持久化类的名称，然后，如果该类声明了任何<union-subclass>,<subclass>或者<joined-subclass>元素，该关联就自然地成为多态。

下面以关联映射中映射的持久化类中声明了<union-subclass>为例：

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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"> <!-- 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/BillingDetails.hbm.xml" /> <mapping resource="pojo/User.hbm.xml" /> </session-factory> </hibernate-configuration>  

pojo/BillingDetails.java:

package pojo;import java.io.Serializable;public abstract class BillingDetails implements Serializable{private String id;private String owner;private User user;public String getId() {return id;}@SuppressWarnings("unused")private void setId(String id) {this.id = id;}public String getOwner() {return owner;}public void setOwner(String owner) {this.owner = owner;}public User getUser() {return user;}public void setUser(User user) {this.user = user;}} 

pojo/CreditCard.java:

package pojo;public class CreditCard extends BillingDetails {private String number;private String expMonth;private String expYear;public String getNumber() {return number;}public void setNumber(String number) {this.number = number;}public String getExpMonth() {return expMonth;}public void setExpMonth(String expMonth) {this.expMonth = expMonth;}public String getExpYear() {return expYear;}public void setExpYear(String expYear) {this.expYear = expYear;}} 

pojo/BankAccount.java:

package pojo;public class BankAccount extends BillingDetails {private String account;private String bankname;private String swift;public String getAccount() {return account;}public void setAccount(String account) {this.account = account;}public String getBankname() {return bankname;}public void setBankname(String bankname) {this.bankname = bankname;}public String getSwift() {return swift;}public void setSwift(String swift) {this.swift = swift;}} 

pojo/BillingDetails.hbm.xml:

<?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="BillingDetails" abstract="true" dynamic-insert="true" dynamic-update="true"> <id name="id" column="ID" type="string"> <generator class="uuid.hex" /> </id> <property name="owner" column="OWNER" type="string"/> <one-to-one name="user" class="User" property-ref="billingDetails"/> <union-subclass name="BankAccount" table="A_BANKACCOUNT"> <property name="account" column="ACCOUNT" type="string"/> <property name="bankname" column="BANKNAME" type="string"/> <property name="swift" column="SWIFT" type="string"/> </union-subclass> <union-subclass name="CreditCard" table="A_CREDITCARD"> <property name="number" column="NUM" type="string"/> <property name="expMonth" column="EXPMONTH" type="string"/> <property name="expYear" column="EXPYEAR" type="string"/> </union-subclass> </class> </hibernate-mapping>  

pojo/User.java:

package pojo;import java.io.Serializable;public class User implements Serializable {private String id;private String name;private int age;private String password;private BillingDetails billingDetails;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 int getAge() {return age;}public void setAge(int age) {this.age = age;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public BillingDetails getBillingDetails() {return billingDetails;}public void setBillingDetails(BillingDetails billingDetails) {this.billingDetails = billingDetails;}} 

pojo/User.hbm.xml:

<?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="User" table="A_USER" dynamic-insert="true" dynamic-update="true"> <id name="id" column="ID" type="string"> <generator class="uuid.hex" /> </id> <property name="name" column="NAME" type="string"/> <property name="age" column="AGE" type="integer"/> <property name="password" column="PASSWORD" type="string"/> <!-- 这里加上unique="true"就成了一对一关联 --> <many-to-one name="billingDetails" class="BillingDetails" column="BILLINGDETAILS_ID" cascade="save-update"/> </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 org.hibernate.Session;import org.hibernate.Transaction;import pojo.BankAccount;import pojo.CreditCard;import pojo.User;public class Manager {@SuppressWarnings("unused")public static void main(String[] args) {BankAccount ba = new BankAccount();ba.setAccount("ba111");ba.setBankname("ba222");ba.setOwner("ba333");ba.setSwift("ba444");User user = new User();user.setAge(30);user.setName("fhd");user.setPassword("999999");user.setBillingDetails(ba);CreditCard cc = new CreditCard();cc.setExpMonth("5");cc.setExpYear("2010");cc.setOwner("ba555");cc.setNumber("55");User user1 = new User();user1.setAge(30);user1.setName("fhd555");user1.setPassword("555555");user1.setBillingDetails(cc);Session session = HibernateUtil.getSessionFactory().openSession();Transaction transaction = session.beginTransaction();session.save(user);session.save(user1);User user3 = (User) session.get(User.class, "402881832b4e5bb4012b4e5bb5050001");/** * 因为默认使用了lazy="true",所以hibernate使用了代理.user3.getBillingDetails()时，返回的是代理类。 * 为了执行代理安全的类型转换，可以使用load() * BankAccount ba = session.load(BankAccount.class,user3.getBillingDetails().getId()); */try {BankAccount ba3 = (BankAccount)user3.getBillingDetails();} catch (ClassCastException e) {System.out.println("类型转换错误");}//导航测试CreditCard cc4 = (CreditCard) session.get(CreditCard.class, "402881832b4e5bb4012b4e5bb50f0004");System.out.println("userName:" + cc4.getUser().getName());transaction.commit();session.close();}} 

表结构：

A_BANKACCOUNT表：ID,OWNER,ACCOUNT,BANKNAME,SWIFTA_CREDITCARD表：ID,OWNER,NUM,EXPMONTH,EXPYEARA_USER表：ID,NAME,AGE,PASSWORD,BILLINGDETAILS_ID