hibernate--继承映射-蒲公英云

对于继承映射表的设计有三种：

以person、student、teacher说明：

一、继承关系树的每个类对应一个表(joined类型)：
Center

Person.java:

package com.bean;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public class Person {
    private int id;
    private String name;
    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

Student.java:

package com.bean;
import javax.persistence.Entity;
@Entity
public class Student extends Person {
    private String num;
    public String getNum() {
        return num;
    }
    public void setNum(String num) {
        this.num = num;
    }
}

Teacher.java:

package com.bean;
import javax.persistence.Entity;
@Entity
public class Teacher extends Person {
    private String title;
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
}

测试类：

package com.test;
import java.util.List;
import java.util.Map;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistryBuilder;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import com.bean.Person;
import com.bean.Student;
import com.bean.Teacher;
public class Test_W_H {
  public static void main(String []args) {
       Configuration cfg = new Configuration();
       cfg.configure(); //加载hibernate配置文件
       SessionFactory sessionFactory = cfg.buildSessionFactory(new ServiceRegistryBuilder().applySettings(cfg.getProperties()).buildServiceRegistry());       
       Session session = sessionFactory.getCurrentSession();
//       Student student = new Student();
//       student.setName("张三");
//       student.setNum("20151080300");
//       
//       Teacher teacher = new Teacher();
//       teacher.setName("Mr.sun");
//       teacher.setTitle("教授");
       session.beginTransaction();  //开启事务
//       session.save(student);
//       session.save(teacher);
       Student student = (Student)session.load(Student.class, 1);
       System.out.println(student.getName());
       Person person = (Person)session.load(Person.class, 2);
       System.out.println(person.getName());
       session.getTransaction().commit(); // 事务提交
       System.out.println("the end");
}
}

Hibernate生成的Hql语句：

Hibernate: 
    select
        student0_.id as id0_0_,
        student0_1_.name as name0_0_,
        student0_.num as num2_0_ 
    from
        Student student0_ 
    inner join
        Person student0_1_ 
            on student0_.id=student0_1_.id 
    where
        student0_.id=?
张三
Hibernate: 
    select
        person0_.id as id0_0_,
        person0_.name as name0_0_,
        person0_1_.title as title1_0_,
        person0_2_.num as num2_0_,
        case 
            when person0_1_.id is not null then 1 
            when person0_2_.id is not null then 2 
            when person0_.id is not null then 0 
        end as clazz_0_ 
    from
        Person person0_ 
    left outer join
        Teacher person0_1_ 
            on person0_.id=person0_1_.id 
    left outer join
        Student person0_2_ 
            on person0_.id=person0_2_.id 
    where
        person0_.id=?
Mr.sun

-——————————————————————————————————————————————-

二、继承关系树的根类对应一个表（single类型）

Center 1

Person.java:

package com.bean;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.DiscriminatorType;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "discriminator",discriminatorType = DiscriminatorType.STRING)
@DiscriminatorValue("person")
public class Person {
    private int id;
    private String name;
    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

Student.java:

package com.bean;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
@Entity
@DiscriminatorValue("student")
public class Student extends Person {
    private String num;
    public String getNum() {
        return num;
    }
    public void setNum(String num) {
        this.num = num;
    }
}

Teacher.java:

package com.bean;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
@Entity
@DiscriminatorValue("teacher")
public class Teacher extends Person {
    private String title;
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
}

-—————————————————————————————————————————————

三、（TABLE_PER_CLASS）

Center 2

Person.java:

package com.bean;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.DiscriminatorType;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.TableGenerator;
@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
@TableGenerator(
        name="person",
        table="GEN_PERSON",
        pkColumnName="P_key",
        valueColumnName="P_value",
        pkColumnValue="person_pk",
        initialValue=1,
        allocationSize=1
        )
public class Person {
    private int id;
    private String name;
    @Id
    @GeneratedValue(strategy=GenerationType.TABLE,generator="person")
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

Student.java:

package com.bean;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
@Entity
public class Student extends Person {
    private String num;
    public String getNum() {
        return num;
    }
    public void setNum(String num) {
        this.num = num;
    }
}

Teacher.java:

package com.bean;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
@Entity
public class Teacher extends Person {
    private String title;
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
}