JPA 系列教程17-继承-独立表-TABLE_PER_CLASS

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 [e-mail]
 * @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 [e-mail]
 * @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 [e-mail]
 * @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 [e-mail]
 * @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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