JPA 系列教程17-继承-独立表-TABLE_PER_CLASS

2022-09-23 23:12:13

PerTable策略

每个具体的类一个表的策略

举例

这种映射策略每个类都会映射成一个单独的表，类的所有属性，包括继承的属性都会映射成表的列。

这种映射策略的缺点是：对多态关系的支持有限，当查询涉及到类继承结构时通常需要发起SQL UNION查询。

配置

注解为：@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)

ddl语句

CREATE TABLE `hibernate_sequences` (

  `sequence_name` varchar(255) DEFAULT NULL,

  `sequence_next_hi_value` int(11) DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `t_person` (

  `id` bigint(20) NOT NULL,

  `name` varchar(255) DEFAULT NULL,

  PRIMARY KEY (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `t_teacher` (

  `id` bigint(20) NOT NULL,

  `name` varchar(255) DEFAULT NULL,

  `address` varchar(255) DEFAULT NULL,

  PRIMARY KEY (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `t_student` (

  `id` bigint(20) NOT NULL,

  `name` varchar(255) DEFAULT NULL,

  `school` varchar(255) DEFAULT NULL,

  PRIMARY KEY (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Person

package com.jege.jpa.extend;

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.Table;

/**

 * @author JE哥

 * @email 1272434821@qq.com

 * @description:父类

 */

@Entity

@Table(name = "t_person")

@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)

public class Person {

  @Id

  // 主键生成方式不能是IDENTITY

  @GeneratedValue(strategy = GenerationType.TABLE)

  private Long id;

  private String name;

  public Long getId() {

    return id;

  }

  public void setId(Long id) {

    this.id = id;

  }

  public String getName() {

    return name;

  }

  public void setName(String name) {

    this.name = name;

  }

}

Teacher

package com.jege.jpa.extend;

import javax.persistence.Entity;

import javax.persistence.Table;

/**

 * @author JE哥

 * @email 1272434821@qq.com

 * @description:子类

 */

@Entity

@Table(name = "t_teacher")

public class Teacher extends Person {

  private String address;

  public String getAddress() {

    return address;

  }

  public void setAddress(String address) {

    this.address = address;

  }

}

Student

package com.jege.jpa.extend;

import javax.persistence.Entity;

import javax.persistence.Table;

/**

 * @author JE哥

 * @email 1272434821@qq.com

 * @description:父子类

 */

@Entity

@Table(name = "t_student")

public class Student extends Person {

  private String school;

  public String getSchool() {

    return school;

  }

  public void setSchool(String school) {

    this.school = school;

  }

}

MainTest

package com.jege.jpa.extend;

import javax.persistence.EntityManager;

import javax.persistence.EntityManagerFactory;

import javax.persistence.Persistence;

import org.junit.After;

import org.junit.AfterClass;

import org.junit.Before;

import org.junit.BeforeClass;

import org.junit.Test;

/**

 * @author JE哥

 * @email 1272434821@qq.com

 * @description:继承测试

 */

public class MainTest {

  private static EntityManagerFactory entityManagerFactory = null;

  private EntityManager entityManager = null;

  @BeforeClass

  public static void setUpBeforeClass() throws Exception {

    entityManagerFactory = Persistence.createEntityManagerFactory("com.jege.jpa");

  }

  @Before

  public void setUp() throws Exception {

    entityManager = entityManagerFactory.createEntityManager();

  }

  @Test

  public void persist() {

    Person person = new Person();

    person.setName("jege");

    Teacher teacher = new Teacher();

    teacher.setName("仓老师");

    teacher.setAddress("北京");

    Student student = new Student();

    student.setName("机械师");

    student.setSchool("上海");

    entityManager.getTransaction().begin();

    entityManager.persist(student);

    entityManager.persist(teacher);

    entityManager.persist(person);

    entityManager.getTransaction().commit();

  }

  @Test

  public void find() {

    persist();

    entityManager.clear();

    Student student = entityManager.find(Student.class, 1L);

    System.out.println(student.getSchool());

  }

  @After

  public void tearDown() throws Exception {

    if (entityManager != null && entityManager.isOpen())

      entityManager.close();

  }

  @AfterClass

  public static void tearDownAfterClass() throws Exception {

    if (entityManagerFactory != null && entityManagerFactory.isOpen())

      entityManagerFactory.close();

  }

}

其他关联项目

JPA 系列教程15-继承-一个表-SINGLE_TABLE

http://blog.csdn.net/je_ge/article/details/53678422
JPA 系列教程16-继承-联合子类-JOINED

http://blog.csdn.net/je_ge/article/details/53678619

源码地址

https://github.com/je-ge/jpa

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