JPA 系列教程17-继承-独立表-TABLE_PER_CLASS

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发布时间：2019-06-09

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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();  }}