JPA 系列教程11-复合主键-2个@Id

复合主键

指多个主键联合形成一个主键组合

需求产生

比如航线一般是由出发地及目的地确定，如果要确定唯一的航线就可以用出发地和目的地一起来表示

ddl语句

CREATE TABLE `t_airline` (
  `startCity` varchar(3) NOT NULL,
  `endCity` varchar(3) NOT NULL,
  `name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`startCity`,`endCity`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Airline

package com.jege.jpa.composite;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 * @author JE哥
 * @email [e-mail]
 * @description:复合主键-2个@Id
 */
@Entity
@Table(name = "t_airline")
public class Airline implements Serializable {
  private static final long serialVersionUID = -906357110051689484L;
  @Id
  @Column(length = 3)
  private String startCity;
  @Id
  @Column(length = 3)
  private String endCity;
  private String name;

  public String getStartCity() {
    return startCity;
  }

  public void setStartCity(String startCity) {
    this.startCity = startCity;
  }

  public String getEndCity() {
    return endCity;
  }

  public void setEndCity(String endCity) {
    this.endCity = endCity;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  @Override
  public String toString() {
    return "Airline [startCity=" + startCity + ", endCity=" + endCity + ", name=" + name + "]";
  }

}

MainTest

package com.jege.jpa.composite;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.PersistenceException;

import org.junit.Test;

/**
 * @author JE哥
 * @email [e-mail]
 * @description:复合主键-2个@Id测试
 */
public class MainTest {
  @Test
  public void crud() {
    EntityManagerFactory entityManagerFactory = null;
    EntityManager entityManager = null;

    try {
      entityManagerFactory = Persistence.createEntityManagerFactory("com.jege.jpa");
      entityManager = entityManagerFactory.createEntityManager();

      Airline airline = new Airline();
      airline.setStartCity("PEK");
      airline.setEndCity("SHA");
      airline.setName("bj to sh");// 新建状态

      entityManager.getTransaction().begin();
      entityManager.persist(airline);// 托管状态

      airline.setName("北京飞上海");

      entityManager.getTransaction().commit();

      Airline airline1 = new Airline();
      airline1.setStartCity("PEK");
      airline1.setEndCity("SHA");

      // hibernate:瞬时状态，持久状态(托管)，游离(脱管)状态

      airline1 = entityManager.find(Airline.class, airline1);
      System.out.println("name:" + airline1.getName());

      entityManager.getTransaction().begin();
      entityManager.remove(airline1);
      entityManager.getTransaction().commit();
      // airline1变为删除状态

      entityManager.getTransaction().begin();
      entityManager.persist(airline1);
      entityManager.getTransaction().commit();
    } catch (PersistenceException e) {
      e.printStackTrace();
      entityManager.getTransaction().rollback();
      throw e;
    } finally {
      if (entityManager != null && entityManager.isOpen())
    entityManager.close();// 游离状态
      if (entityManagerFactory != null && entityManagerFactory.isOpen())
    entityManagerFactory.close();
    }
  }
}

源码地址

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

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