这里详细讨论继承映射的3种方式：
1.Table per concrete class
继承关系如下图：
数据表设计如下图：
mysql数据库中执行如下DDL：
1.CREATE TABLE defaultuser (<br />2. id INT(11) NOT NULL auto_increment PRIMARY KEY,<br />3. name VARCHAR(100) NOT NULL default '',<br />4. someProperty VARCHAR(100)<br />5.);<br />6.<br />7.CREATE TABLE poweruser (<br />8. id INT(11) NOT NULL auto_increment PRIMARY KEY,<br />9. name VARCHAR(100) NOT NULL default '',<br />10. otherProperty VARCHAR(100)<br />11.);
User.java
1.package com.hb3.pack_08.model;<br />2.<br />3.public class User {<br />4.5. private Integer id;<br />6. private String name;<br />7.<br />8. public User() {<br />9. }<br />10.11. public Integer getId() {<br />12. return id;<br />13. }<br />14. public void setId(Integer id) {<br />15. this.id = id;<br />16. }<br />17. public String getName() {<br />18. return name;<br />19. }<br />20. public void setName(String name) {<br />21. this.name = name;<br />22. }<br />23.}
DefaultUser.java
1.package com.hb3.pack_08.model;<br />2.<br />3.public class DefaultUser extends User {<br />4.5. private String someProperty;<br />6.7. public DefaultUser() {<br />8. }<br />9.10. public String getSomeProperty() {<br />11. return someProperty;<br />12. }<br />13. public void setSomeProperty(String someProperty) {<br />14. this.someProperty = someProperty;<br />15. }<br />16.}
PowerUser.java
1.package com.hb3.pack_08.model;<br />2.<br />3.public class PowerUser extends User {<br />4.5. private String otherProperty;<br />6.<br />7. public PowerUser() {<br />8. }<br />9.10. public String getOtherProperty() {<br />11. return otherProperty;<br />12. }<br />13. public void setOtherProperty(String otherProperty) {<br />14. this.otherProperty = otherProperty;<br />15. }<br />16.}
DefaultUser.hbm.xml文件：
1.<?xml version="1.0" encoding="UTF-8"?><br />2.3.<!DOCTYPE hibernate-mapping PUBLIC<br />4. "-//Hibernate/Hibernate Mapping DTD 3.0//EN"<br />5. "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">6.7.<hibernate-mapping>8.9. <class name="com.hb3.pack_08.model.DefaultUser" table="defaultuser"><br />10.<br />11. <id name="id" column="id" type="java.lang.Integer"><br />12. <generator class="native"/><br />13. </id><br />14.<br />15. <property name="name" column="name" type="java.lang.String"/><br />16.<br />17. <property name="someProperty" column="someProperty" type="java.lang.String"/><br />18.<br />19. </class><br />20.<br />21.</hibernate-mapping>
PowerUser.hbm.xml文件：
1.<?xml version="1.0" encoding="UTF-8"?><br />2.3.<!DOCTYPE hibernate-mapping PUBLIC<br />4. "-//Hibernate/Hibernate Mapping DTD 3.0//EN"<br />5. "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">6.7.<hibernate-mapping>8.9. <class name="com.hb3.pack_08.model.PowerUser" table="poweruser">10.<br />11. <id name="id" column="id" type="java.lang.Integer"><br />12. <generator class="native"/><br />13. </id><br />14.<br />15. <property name="name" column="name" type="java.lang.String"/><br />16.<br />17. <property name="otherProperty" column="otherProperty" type="java.lang.String"/><br />18.<br />19. </class><br />20.<br />21.</hibernate-mapping>
修改hibernate.cfg.xml文件：
......
……
1.package com.hb3.pack_08;2.3.import java.io.IOException;4.import java.sql.SQLException;5.import java.util.Iterator;6.7.import org.hibernate.Query;8.import org.hibernate.Session;9.import org.hibernate.SessionFactory;10.import org.hibernate.Transaction;11.import org.hibernate.cfg.Configuration;12.
13.import com.hb3.pack_08.model.DefaultUser;14.import com.hb3.pack_08.model.PowerUser;15.import com.hb3.pack_08.model.User;16.17.public class BusinessService {18.19. public static void main(String[] args) throws IOException, SQLException {20.21. Configuration config = new Configuration().configure();22. SessionFactory sessionFactory = config.buildSessionFactory();23. Session session = sessionFactory.openSession();24.25.26. DefaultUser defaultUser = new DefaultUser();27. defaultUser.setName(“chenyan”);28. defaultUser.setSomeProperty(“hu….hu…”);29.30. PowerUser powerUser = new PowerUser();31. powerUser.setName(“shenbin”);32. powerUser.setOtherProperty(“Bla…Bla…”);33.34. Transaction tx = session.beginTransaction();35. session.save(powerUser);36. session.save(defaultUser);37. tx.commit();38.39.40. session.close();41. session = sessionFactory.openSession();42.43.44. Query query = session.createQuery(“from com.hb3.pack_08.model.User”);45. Iterator iterator = query.list().iterator();46. while(iterator.hasNext()) {47. User user = (User) iterator.next();48. System.out.println(user.getName());49. }50.51.52. session.close();53. sessionFactory.close();54. }55.}
请注意：查询中查询的是User，所以会找出所有DefaultUser和PowerUser的资料。User类中不包括的他子类特有的字段也会被找到。
值得一提的是，查询中如果直接使用”from java.lang.Object”这样的HQL的话，将查出数据库中所有的数据资料。因为Object是Java中所有类的父类。
2.Table per class hierarchy
数据表设计如下图：
DDL文件：
1.CREATE TABLE user (<br />2. id INT(11) NOT NULL auto_increment PRIMARY KEY,<br />3. userType VARCHAR(50) NOT NULL,<br />4. name VARCHAR(100) NOT NULL default '',<br />5. someProperty VARCHAR(100),<br />6. otherProperty VARCHAR(100)<br />7.);
POJO同上，分为：User，PowerUser，DefaultUser。
User.hbm.xml文件：
1.<?xml version="1.0" encoding="utf-8"?><br />2.<!DOCTYPE hibernate-mapping <br />3. PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"<br />4. "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><br />5.<br />6.<hibernate-mapping><br />7.8. <class name="com.hb3.pack_09.model.User" table="user"><br />9.<br />10. <id name="id" column="id" type="java.lang.Integer"><br />11. <generator class="native"/><br />12. </id><br />13.<br />14. <discriminator column="userType" type="java.lang.String"/><br />15.<br />16. <property name="name" column="name" type="java.lang.String"/><br />17.<br />18. <subclass name="com.hb3.pack_09.model.DefaultUser"<br />19. discriminator-value="Default"><br />20.<br />21. <property name="someProperty"<br />22. column="someProperty"<br />23. type="java.lang.String"/><br />24. </subclass><br />25.<br />26. <subclass name="com.hb3.pack_09.model.PowerUser"<br />27. discriminator-value="Power"><br />28.<br />29. <property name="otherProperty"<br />30. column="otherProperty"<br />31. type="java.lang.String"/><br />32. </subclass>33.<br />34. </class>35.<br />36.</hibernate-mapping>
修改hibernate.cfg.xml文件：
............
测试代码也和上面的基本一致:
1.package com.hb3.pack_09;<br />2.<br />3.import java.io.IOException;<br />4.import java.sql.SQLException;<br />5.import java.util.Iterator;<br />6.7.import org.hibernate.Query;<br />8.import org.hibernate.Session;<br />9.import org.hibernate.SessionFactory;<br />10.import org.hibernate.Transaction;<br />11.import org.hibernate.cfg.Configuration;<br />12.13.import com.hb3.pack_09.model.DefaultUser;<br />14.import com.hb3.pack_09.model.PowerUser;<br />15.import com.hb3.pack_09.model.User;<br />16.17.public class BusinessService {<br />18.19. public static void main(String[] args) throws IOException, SQLException {<br />20.<br />21. Configuration config = new Configuration().configure();<br />22. SessionFactory sessionFactory = config.buildSessionFactory();<br />23. Session session = sessionFactory.openSession();<br />24.25.<br />26. DefaultUser defaultUser = new DefaultUser();<br />27. defaultUser.setName("chenyan");<br />28. defaultUser.setSomeProperty("hu....hu...");<br />29.<br />30. PowerUser powerUser = new PowerUser();<br />31. powerUser.setName("shenbin");<br />32. powerUser.setOtherProperty("Bla...Bla...");<br />33.34. Transaction tx = session.beginTransaction();<br />35. session.save(powerUser);<br />36. session.save(defaultUser);<br />37. tx.commit();<br />38.<br />39.<br />40. session.close();<br />41. session = sessionFactory.openSession();<br />42.<br />43.<br />44. Query query = session.createQuery("from com.hb3.pack_09.model.User");<br />45. Iterator<?> iterator = query.list().iterator();<br />46. while(iterator.hasNext()) {<br />47. User user = (User) iterator.next();<br />48. System.out.println(user.getName());<br />49. }<br />50.<br />51.<br />52. session.close();<br />53. sessionFactory.close();<br />54. }<br />55.}
3.Table per subclass
数据表设计如下图：
DDL文件：
1.CREATE TABLE user (<br />2. id INT(11) NOT NULL auto_increment PRIMARY KEY,<br />3. name VARCHAR(100) NOT NULL default ''<br />4.);<br />5.<br />6.CREATE TABLE defaultuser (<br />7. id INT(11) NOT NULL PRIMARY KEY,<br />8. someProperty VARCHAR(100)<br />9.);<br />10.11.CREATE TABLE poweruser (<br />12. id INT(11) NOT NULL PRIMARY KEY,<br />13. otherProperty VARCHAR(100)<br />14.);
POJO同上，分为：User，PowerUser，DefaultUser。
User.hbm.xml文件：
1.<?xml version="1.0" encoding="utf-8"?><br />2.<!DOCTYPE hibernate-mapping <br />3. PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"<br />4. "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><br />5.<br />6.<hibernate-mapping><br />7.<br />8. <class name="com.hb3.pack_10.model.User" table="user"><br />9.<br />10. <id name="id" column="id" type="java.lang.Integer"><br />11. <generator class="native"/><br />12. </id><br />13.<br />14. <property name="name" column="name" type="java.lang.String"/><br />15.<br />16. <joined-subclass name="com.hb3.pack_10.model.DefaultUser"<br />17. table="defaultuser">18.<br />19. <key column="id"/><br />20.<br />21. <property name="someProperty"<br />22. column="someProperty"<br />23. type="java.lang.String"/><br />24.<br />25. </joined-subclass><br />26.<br />27. <joined-subclass name="com.hb3.pack_10.model.PowerUser"<br />28. table="poweruser"><br />29.<br />30. <key column="id"/><br />31.<br />32. <property name="otherProperty"<br />33. column="otherProperty"<br />34. type="java.lang.String"/><br />35.<br />36. </joined-subclass><br />37.<br />38. </class><br />39.<br />40.</hibernate-mapping>
修改hibernate.cfg.xml文件：
............
测试代码如下：
1.package com.hb3.pack_10;<br />2.<br />3.import java.io.IOException;<br />4.import java.sql.SQLException;<br />5.import java.util.Iterator;<br />6.<br />7.import org.hibernate.Query;<br />8.import org.hibernate.Session;<br />9.import org.hibernate.SessionFactory;<br />10.import org.hibernate.Transaction;<br />11.import org.hibernate.cfg.Configuration;<br />12.<br />13.import com.hb3.pack_10.model.DefaultUser;<br />14.import com.hb3.pack_10.model.PowerUser;<br />15.import com.hb3.pack_10.model.User;<br />16.17.public class BusinessService {<br />18.19. public static void main(String[] args) throws IOException, SQLException {<br />20.<br />21. Configuration config = new Configuration().configure();<br />22. SessionFactory sessionFactory = config.buildSessionFactory();<br />23. Session session = sessionFactory.openSession();<br />24.25.<br />26. DefaultUser defaultUser = new DefaultUser();<br />27. defaultUser.setName("chenyan");<br />28. defaultUser.setSomeProperty("hu....hu...");<br />29.<br />30. PowerUser powerUser = new PowerUser();<br />31. powerUser.setName("shenbin");<br />32. powerUser.setOtherProperty("Bla...Bla...");<br />33.34. Transaction tx = session.beginTransaction();<br />35. session.save(powerUser);<br />36. session.save(defaultUser);<br />37. tx.commit();<br />38.<br />39.<br />40. session.close();<br />41. session = sessionFactory.openSession();<br />42.<br />43.<br />44. Query query = session.createQuery("from com.hb3.pack_10.model.User");<br />45. Iterator<?> iterator = query.list().iterator();<br />46. while(iterator.hasNext()) {<br />47. User user = (User) iterator.next();<br />48. System.out.println(user.getName());<br />49. }<br />50.<br />51.<br />52. session.close();<br />53. sessionFactory.close();<br />54. }<br />55.}
也许不是自己该去发挥的地方，还是让自己到最适合自己战斗的方面去吧!勇敢的接受自己的失败，
