Hibernate 再接触 继承映射

用一张

每一个类一张表

建立外键

第一种 一张总表

Person

package com.bjsxt.hibernate;

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.

package com.bjsxt.hibernate;

import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;

@Entity
@DiscriminatorValue("student")
public class Student extends Person {
    
    private int score;

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }
    
}

Teacher

package com.bjsxt.hibernate;

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;
    }

    
}

testsave

package com.bjsxt.hibernate;

import java.util.Map;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;

public class HibernateORMappingTest {
    private static SessionFactory sessionFactory;
    
    @BeforeClass
    public static void beforeClass() {
        new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
        sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
    }
    @AfterClass
    public static void afterClass() {
        sessionFactory.close();
    }
    
    @Test
    public void testSave() {
        Student s = new Student();
        s.setName("s1");
        s.setScore(80);
        Teacher t = new Teacher();
        t.setName("t1");
        t.setTitle("中级");
        
        Session session = sessionFactory.openSession();
        session.beginTransaction();
        session.save(s);
        session.save(t);
        session.getTransaction().commit();
        session.close();
    }
    @Test
    public void testLoad() {
        
        testSave();
        Session session = sessionFactory.openSession();
        session.beginTransaction();
        Student s = (Student)session.load(Student.class, 1);
        System.out.println(s.getScore());
        Person p = (Person)session.load(Person.class, 2);
        System.out.println(p.getName());
        session.getTransaction().commit();
        session.close();
        
    }
    
    @Test
    public void testSchemaExport() {
        new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
    }
    
    
    public static void main(String[] args) {
        beforeClass();
    }
}

testload

    @Test
    public void testLoad() {
        
        testSave();
        Session session = sessionFactory.openSession();
        session.beginTransaction();
        Student s = (Student)session.load(Student.class, 1);
        System.out.println(s.getScore());
        Person p = (Person)session.load(Person.class, 2);
        System.out.println(p.getName());
        session.getTransaction().commit();
        session.close();
        
    }

这种方式会产生大量冗余字段 比如存Teacher会导致score为空等 适合数据量少使用

第二种方式 每一个类一个表

Person

package com.bjsxt.hibernate;

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="t_gen",
        table="t_gen_table",
        pkColumnName="t_pk",
        valueColumnName="t_value",
        pkColumnValue="person_pk",
        initialValue=1,
        allocationSize=1
        )
public class Person {
    private int id;
    private String name;
    
    @Id
    @GeneratedValue(generator="t_gen", strategy=GenerationType.TABLE)
    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

package com.bjsxt.hibernate;

import javax.persistence.Entity;

@Entity
public class Student extends Person {
    
    private int score;

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }
    
}

teacher

package com.bjsxt.hibernate;

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;
    }

    
}

testsave

    @Test
    public void testSave() {
        Student s = new Student();
        s.setName("s1");
        s.setScore(80);
        Teacher t = new Teacher();
        t.setName("t1");
        t.setTitle("中级");
        
        Session session = sessionFactory.openSession();
        session.beginTransaction();
        session.save(s);
        session.save(t);
        session.getTransaction().commit();
        session.close();
    }

testload

    @Test
    public void testLoad() {
        testSave();
        Session session = sessionFactory.openSession();
        session.beginTransaction();
        Student s = (Student)session.load(Student.class, 1);
        System.out.println(s.getScore());
        Person p = (Person)session.load(Person.class, 2);   //会从teacher和student中取出数据 联合生成一个表，然后从里面找出id为2的
        System.out.println(p.getName());
        session.getTransaction().commit();
        session.close();
        

第三种方式 外键关联

Person

package com.bjsxt.hibernate;

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;
    }

}

Teache

package com.bjsxt.hibernate;

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;
    }

    
}

student

package com.bjsxt.hibernate;

import javax.persistence.Entity;

@Entity
public class Student extends Person {
    
    private int score;

    public int getScore() {
        return score;
    } //Person p = Person(load(1));

    public void setScore(int score) {
        this.score = score;
    }
    
}

testsave

package com.bjsxt.hibernate;

import javax.persistence.Entity;

@Entity
public class Student extends Person {
    
    private int score;

    public int getScore() {
        return score;
    } //Person p = Person(load(1));

    public void setScore(int score) {
        this.score = score;
    }
    
}

testload

    @Test
    public void testLoad() {
        testSave();
        Session session = sessionFactory.openSession();
        session.beginTransaction();
        Student s = (Student)session.load(Student.class, 1);
        System.out.println(s.getScore());
        Person p = (Person)session.load(Person.class, 2);   //合成一个表取出来数据
        System.out.println(p.getName());
        session.getTransaction().commit();
        session.close();
        
    }

一般来说 用第三种和第一种比较多