JPA 一對(duì)一映射示例

JPA教程 - JPA 一對(duì)一映射示例

本節(jié)介紹如何在JPA映射中執(zhí)行一對(duì)一映射。

此示例假設(shè)一個(gè)人只能是一個(gè)部門的一部分，而一個(gè)部門只能有一個(gè)人。

在Person實(shí)體中，我們使用@OneToOne注釋標(biāo)記Department引用屬性。

@Entity
public class Person {

...
@OneToOne
private Department department;
...

這里是設(shè)置兩個(gè)實(shí)體并將它們保存到數(shù)據(jù)庫(kù)的簡(jiǎn)單代碼。

    Person p1 = new Person("Tom");
    
    p1.setName("Tom");
    
    Department d = new Department();
    d.setName("Design");
    p1.setDepartment(d);
    
    em.persist(p1);
    em.persist(d);

例子

下面的代碼來自Person.java。

package cn.w3cschool.common;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToOne;

@Entity
public class Person {
  @Id
  @GeneratedValue(strategy=GenerationType.IDENTITY)
  private long id;
   
  private String name;
  @OneToOne
  private Department department;
  
  public Person() {}

  public Person(String name) {
    this.name = name;
  }


  public Department getDepartment() {
    return department;
  }

  public void setDepartment(Department department) {
    this.department = department;
  }

  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;
  }

  @Override
  public String toString() {
    return "Person [id=" + id + ", name=" + name + "]";
  }

}

下面的代碼來自Department.java。

package cn.w3cschool.common;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Department {
  @Id
  @GeneratedValue(strategy=GenerationType.IDENTITY)
  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;
  }
}

下面的代碼來自PersonDaoImpl.java。

package cn.w3cschool.common;


import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import org.springframework.transaction.annotation.Transactional;

@Transactional
public class PersonDaoImpl {
  public void test(){
    Person p1 = new Person("Tom");
    
    p1.setName("Tom");
    
    Department d = new Department();
    d.setName("Design");
    p1.setDepartment(d);
    
    em.persist(p1);
    em.persist(d);
  }
  @PersistenceContext
  private EntityManager em;
}

以下是數(shù)據(jù)庫(kù)轉(zhuǎn)儲(chǔ)。

Table Name: DEPARTMENT
 Row:
    Column Name: ID,
    Column Type: BIGINT:
    Column Value: 1

    Column Name: NAME,
    Column Type: VARCHAR:
    Column Value: Design
Table Name: PERSON
 Row:
    Column Name: ID,
    Column Type: BIGINT:
    Column Value: 1

    Column Name: NAME,
    Column Type: VARCHAR:
    Column Value: Tom

    Column Name: DEPARTMENT_ID,
    Column Type: BIGINT:
    Column Value: 1