JPA 系列教程12-复合主键-2个@Id+@IdClass

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

同复合主键-2个@Id一样

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.IdClass;
import javax.persistence.Table;

/**
 * @author JE哥
 * @email [email protected]
 * @description:复合主键-2个@Id+@IdClass
 */
@Entity
@Table(name = "t_airline")
@IdClass(Airline.AirlinePK.class)
public class Airline {
  @Id
  private String startCity;
  @Id
  private String endCity;
  private String name;

  public String getName() {
    return name;
  }

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

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

  // 必须static的class
  public static class AirlinePK implements Serializable {
    private static final long serialVersionUID = -7189167162738318201L;
    @Column(length = 3, nullable = false)
    private String startCity;
    @Column(length = 3, nullable = false)
    private String endCity;

    public AirlinePK() {
    }

    public AirlinePK(String startCity, String endCity) {
      this.startCity = startCity;
      this.endCity = endCity;
    }

    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;
    }

    @Override
    public int hashCode() {
      final int prime = 31;
      int result = 1;
      result = prime * result + ((endCity == null) ? 0 : endCity.hashCode());
      result = prime * result + ((startCity == null) ? 0 : startCity.hashCode());
      return result;
    }

    @Override
    public boolean equals(Object obj) {
      if (this == obj)
    return true;
      if (obj == null)
    return false;
      if (getClass() != obj.getClass())
    return false;
      AirlinePK other = (AirlinePK) obj;
      if (endCity == null) {
    if (other.endCity != null)
      return false;
      } else if (!endCity.equals(other.endCity))
    return false;
      if (startCity == null) {
    if (other.startCity != null)
      return false;
      } else if (!startCity.equals(other.startCity))
    return false;
      return true;
    }

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

  }

}

MainTest

package com.jege.jpa.composite;

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;

import com.jege.jpa.composite.Airline.AirlinePK;

/**
 * @author JE哥
 * @email [email protected]
 * @description:复合主键-2个@Id+@IdClass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() {
    Airline airline = new Airline();
    airline.setEndCity("SHA");
    airline.setStartCity("PEK");
    airline.setName("北京飞上海");

    entityManager.getTransaction().begin();
    entityManager.persist(airline);
    entityManager.getTransaction().commit();
  }

  @Test
  public void find() {
    persist();

    AirlinePK pk = new AirlinePK("PEK", "SHA");
    Airline airline = entityManager.find(Airline.class, pk);
    System.out.println(airline);
  }

  @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11-复合主键-2个@Id
  http://blog.csdn.net/je_ge/article/details/53678085

源码地址

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

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