使用xml文件的每个层次结构的Hibernate表 Hibernate表|Hibernate

通过这种继承策略, 我们只能按单个表映射整个层次结构。在此, 在表中创建了一个额外的列（也称为鉴别符列）以标识类。
让我们首先了解问题。我想将下面给出的整个层次结构映射到数据库的一个表中。

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此层次结构中有三个类。 Employee是Regular_Employee和Contract_Employee类的超类。让我们看看该层次结构的映射文件。

< ?xml version='1.0' encoding='UTF-8'?> < !DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 5.3//EN" "http://hibernate.sourceforge.net/hibernate-mapping-5.3.dtd"> < hibernate-mapping> < class name="com.srcmini.mypackage.Employee" table="emp121" discriminator-value="http://www.srcmini.com/emp"> < id name="id"> < generator class="increment"> < /generator> < /id> < discriminator column="type" type="string"> < /discriminator> < property name="name"> < /property> < subclass name="com.srcmini.mypackage.Regular_Employee" discriminator-value="http://www.srcmini.com/reg_emp"> < property name="salary"> < /property> < property name="bonus"> < /property> < /subclass> < subclass name="com.srcmini.mypackage.Contract_Employee" discriminator-value="http://www.srcmini.com/con_emp"> < property name="pay_per_hour"> < /property> < property name="contract_duration"> < /property> < /subclass> < /class> < /hibernate-mapping>

对于每个类层次结构的表, hibernate框架会添加一个区分符列, 以指定记录的类型。它主要用于区分记录。为此, 必须指定类别的鉴别子元素。

class的subclass子元素, 指定子类。在这种情况下, Regular_Employee和Contract_Employee是Employee类的子类。

该层次结构的表结构如下所示：

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每个类层次结构表的示例
在此示例中, 我们将创建三个类, 并在employee.hbm.xml文件中提供这些类的映射。
1）创建持久类
你需要创建表示继承的持久类。让我们为上述层次结构创建三个类：
文件：Employee.java

package com.srcmini.mypackage; public class Employee { private int id; private String name; //getters and setters }

文件：Regular_Employee.java

package com.srcmini.mypackage; public class Regular_Employee extends Employee{ private float salary; private int bonus; //getters and setters }

文件：Contract_Employee.java

package com.srcmini.mypackage; public class Contract_Employee extends Employee{ private float pay_per_hour; private String contract_duration; //getters and setters }

2）为Persistent类创建映射文件
上面已经针对层次结构讨论了映射。
文件：employee.hbm.xml

< ?xml version='1.0' encoding='UTF-8'?> < !DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 5.3//EN" "http://hibernate.sourceforge.net/hibernate-mapping-5.3.dtd"> < hibernate-mapping> < class name="com.srcmini.mypackage.Employee" table="emp121" discriminator-value="http://www.srcmini.com/emp"> < id name="id"> < generator class="increment"> < /generator> < /id> < discriminator column="type" type="string"> < /discriminator> < property name="name"> < /property> < subclass name="com.srcmini.mypackage.Regular_Employee" discriminator-value="http://www.srcmini.com/reg_emp"> < property name="salary"> < /property> < property name="bonus"> < /property> < /subclass> < subclass name="com.srcmini.mypackage.Contract_Employee" discriminator-value="http://www.srcmini.com/con_emp"> < property name="pay_per_hour"> < /property> < property name="contract_duration"> < /property> < /subclass> < /class> < /hibernate-mapping>

3）在配置文件中添加hbm文件的映射
打开hibernate.cgf.xml文件, 并添加如下所示的映射资源条目：

< mapping resource="employee.hbm.xml"/>

现在, 配置文件将如下所示：
文件：hibernate.cfg.xml

< ?xml version='1.0' encoding='UTF-8'?> < !DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 5.3//EN" "http://hibernate.sourceforge.net/hibernate-configuration-5.3.dtd"> < hibernate-configuration> < session-factory> < property name="hbm2ddl.auto"> update< /property> < property name="dialect"> org.hibernate.dialect.Oracle9Dialect< /property> < property name="connection.url"> jdbc:oracle:thin:@localhost:1521:xe< /property> < property name="connection.username"> system< /property> < property name="connection.password"> jtp< /property> < property name="connection.driver_class"> oracle.jdbc.driver.OracleDriver< /property> < mapping resource="employee.hbm.xml"/> < /session-factory> < /hibernate-configuration>

定义了hbm2ddl.auto属性, 用于在数据库中创建自动表。
4）创建存储持久对象的类
在此类中, 我们仅将雇员对象存储在数据库中。
文件：StoreData.java

package com.srcmini.mypackage; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import org.hibernate.boot.Metadata; import org.hibernate.boot.MetadataSources; import org.hibernate.boot.registry.StandardServiceRegistry; import org.hibernate.boot.registry.StandardServiceRegistryBuilder; public class StoreData { public static void main(String[] args) { StandardServiceRegistry ssr=new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build(); Metadata meta=new MetadataSources(ssr).getMetadataBuilder().build(); SessionFactory factory=meta.getSessionFactoryBuilder().build(); Session session=factory.openSession(); Transaction t=session.beginTransaction(); Employee e1=new Employee(); e1.setName("Gaurav Chawla"); Regular_Employee e2=new Regular_Employee(); e2.setName("Vivek Kumar"); e2.setSalary(50000); e2.setBonus(5); Contract_Employee e3=new Contract_Employee(); e3.setName("Arjun Kumar"); e3.setPay_per_hour(1000); e3.setContract_duration("15 hours"); session.persist(e1); session.persist(e2); session.persist(e3); t.commit(); session.close(); System.out.println("success"); } }

输出：