Hibernate映射类继承之混合继承策略

来源：互联网发布：mysql 删除某一字段编辑：程序博客网时间：2024/04/26 11:37

通过嵌套<union-subclass>,<subclass>,和<joined-subclass>映射元素可以映射整个继承层次结构。你无法把它们混合起来---例如，用一个辨别标志从"每个类层次结构一张表"策略转换到标准的"每个类一张表"策略。一旦决定使用某种继承策略，就必须坚持使用它。但这并不完全正确，使用一些hibernate技巧，可以给一个特定的子类切换映射策略。例如，可以把一个类层次结构映射到单张表，但是对于特定的子类，则通过外键映射策略切换到单独的表，就像使用"每个类一张表"一样。使用<join>映射元素，这种转换是可能的。

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/BillingDetails.hbm.xml" /> </session-factory> </hibernate-configuration>

父类，pojo/BillingDetails.java:

package pojo;public class BillingDetails {private String id;private String owner;public String getOwner() {return owner;}public void setOwner(String owner) {this.owner = owner;}public String getId() {return id;}public void setId(String id) {this.id = id;}}

子类，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;}}

子类,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;}}

映射文件,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" table="BILLING_DETAILS" dynamic-insert="true" dynamic-update="true"> <id name="id" column="BILLING_DETAILS_ID" type="string"> <generator class="uuid.hex" /> </id> <discriminator column="BILLING_DETAILS_TYPE" type="string"/> <property name="owner" column="OWNER" type="string" /> <subclass name="CreditCard" discriminator-value="CC"> <join table="CREDIT_CARD"> <key column="CREDIT_CARD_ID"/> <property name="number" column="CC_NUMBER" type="string"/> <property name="expMonth" column="CC_EXP_MONTH" type="string"/> <property name="expYear" column="CC_EXP_YEAR" type="string"/> </join> </subclass> <subclass name="BankAccount" discriminator-value="BA"> <property name="account" column="BA_ACCOUNT" type="string"/> <property name="bankName" column="BA_BANKNAME" type="string"/> <property name="swift" column="BA_SWIFT" type="string"/> </subclass> </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;public class Manager {public static void main(String[] args) {BankAccount ba = new BankAccount();ba.setAccount("个人帐户");ba.setBankName("付海东");ba.setOwner("fuhaidong");ba.setSwift("aaa");CreditCard cc = new CreditCard();cc.setOwner("fuhaidong");cc.setNumber("100000000");cc.setExpYear("2010");cc.setExpMonth("10");Session session = HibernateUtil.getSessionFactory().openSession();Transaction transaction = session.beginTransaction();//插入session.save(cc);session.save(ba);session.createQuery("from CreditCard").list();session.createQuery("from BankAccount").list();transaction.commit();session.close();}}

输出的sql:

Hibernate: insert into BILLING_DETAILS (OWNER, BILLING_DETAILS_TYPE, BILLING_DETAILS_ID) values (?, 'CC', ?)Hibernate: insert into CREDIT_CARD (CC_NUMBER, CC_EXP_MONTH, CC_EXP_YEAR, CREDIT_CARD_ID) values (?, ?, ?, ?)Hibernate: insert into BILLING_DETAILS (OWNER, BA_ACCOUNT, BA_BANKNAME, BA_SWIFT, BILLING_DETAILS_TYPE, BILLING_DETAILS_ID) values (?, ?, ?, ?, 'BA', ?)Hibernate: select creditcard0_.BILLING_DETAILS_ID as BILLING1_0_, creditcard0_.OWNER as OWNER0_, creditcard0_1_.CC_NUMBER as CC2_1_, creditcard0_1_.CC_EXP_MONTH as CC3_1_, creditcard0_1_.CC_EXP_YEAR as CC4_1_ from BILLING_DETAILS creditcard0_, CREDIT_CARD creditcard0_1_ where creditcard0_.BILLING_DETAILS_TYPE='CC' and creditcard0_.BILLING_DETAILS_ID=creditcard0_1_.CREDIT_CARD_IDHibernate: select bankaccoun0_.BILLING_DETAILS_ID as BILLING1_0_, bankaccoun0_.OWNER as OWNER0_, bankaccoun0_.BA_ACCOUNT as BA4_0_, bankaccoun0_.BA_BANKNAME as BA5_0_, bankaccoun0_.BA_SWIFT as BA6_0_ from BILLING_DETAILS bankaccoun0_ where bankaccoun0_.BILLING_DETAILS_TYPE='BA'

这里有两张表：

<BILLING_DETAILS>表

BILLING_DETAILS_ID

BILLING_DETAILS_TYPE

OWNER

BA_ACCOUNT

BA_BANKNAME

BA_SWIFT

<CREDIT_CARD>表

CREDIT_CARD_ID

CC_NUMBER

CC_EXP_MONTH

CC_EXP_YEAR